Audio signal processing method and device for controlling loudness level

Abstract

To reproduce audio signals effectively.SOLUTION: An audio signal processing device comprises: a receiver for receiving an input audio signal; a processor for generating loudness metadata corresponding to the input audio signal; and an output unit for transmitting the loudness metadata generated by the processor. The processor is configured to: acquire loudness information analyzed from input content; acquire loudness information on the input audio signal by measuring the loudness of the input audio signal; generate the loudness metadata by converting the loudness information; and transmit, through the output unit, the generated loudness metadata to an output device for outputting the input audio signal.SELECTED DRAWING: Figure 19

Description

[Technical field]

[0001] The present invention relates to an audio signal processing method and device for effectively reproducing an audio signal, and more particularly to an audio signal processing method and device for adjusting the loudness level at which an audio signal of content is output and providing a user with a more immersive audio signal. [Background technology]

[0002] As the method of providing audio to users has changed from analog to digital, a wider range of volume can be expressed. In addition, the volume of audio signals is becoming more diverse depending on the content corresponding to the audio signal. In the process of producing audio content, the intended loudness can be set differently for each audio content. For this reason, international standardization organizations such as the International Telecommunication Union (ITU) and the European Broadcasting Union (EBU) have issued standards for audio loudness. However, since the methods and standards for measuring loudness differ from country to country, it is difficult to apply the standards issued by the international standardization organizations.

[0003] Content producers try to produce and provide users with content that is mixed with a relatively louder sound. This is because of a psychological acoustic characteristic in which an increase in the sound volume of an audio signal is perceived as an improvement in the sound quality of the audio signal. As a result, a competitive structure called the Loudness War has been formed. As a result, loudness differences occur within a content or between multiple contents, which can cause inconvenience to users who have to repeatedly adjust the volume of the device on which the content is reproduced. Therefore, a technology for normalizing the loudness of audio content is desired for the convenience of users who use content reproduction devices. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of one embodiment of the present invention is to efficiently adjust an output loudness level of content that includes an audio signal in an audio signal processing method for reproducing the content. [Means for solving the problem]

[0005] According to an embodiment of the present invention, an audio signal processing device includes a receiving unit for receiving an input audio signal, a processor for generating loudness metadata corresponding to the input audio signal, and an output unit for transmitting the loudness metadata generated by the processor. The processor may measure the loudness of the input audio signal to obtain loudness information of the input audio signal, convert the loudness information to generate the loudness metadata, and transmit the generated loudness metadata from the output unit to an output device that outputs the input audio signal. The loudness information includes information indicating a Quality Secure Histogram Index (QSHI) of the input audio signal, and the QSHI indicates a threshold loudness level at which no cognitive sound quality impairment occurs.

[0006] The processor may obtain the QSHI based on a loudness histogram of the input audio signal.

[0007] The processor may obtain the loudness histogram based on a distribution of short-term loudness levels of at least one of the input audio signals, and obtain the QSHI based on the loudness histogram. The short-term loudness levels may be measured over a period shorter than the entire period of the input audio signal.

[0008] The loudness histogram may be a size histogram relating to peak values ​​or root-mean-square (RMS) for each section of the input audio signal.

[0009] The processor can predict loudness parameters when the input audio signal is output according to a target loudness level based on a loudness histogram of the input audio signal, obtain a predicted loudness histogram of the input audio signal based on the predicted loudness parameters, and obtain the QSHI based on the predicted loudness predicted histogram.

[0010] The loudness information may include a cumulative loudness level of the input audio signal, the QSHI may be greater than the cumulative loudness level of the input audio signal, and the cumulative loudness level may be a loudness level calculated based on loudness measurement values ​​obtained from a setup point in time set in an audio signal processing device.

[0011] The QSHI may be a parameter that is corrected depending on whether or not post processing is performed on the input audio signal in the output device.

[0012] The processor can set the QSHI so that the short-term loudness level of the entire section of the input audio signal output from the output device is equal to or lower than a previously set level.

[0013] According to another aspect of the present invention, an audio signal processing apparatus includes a processor for adjusting an output loudness level of an input audio signal. The processor may receive loudness metadata corresponding to the input audio signal, parse the loudness metadata to obtain loudness information of the input audio signal, determine a loudness gain of the input audio signal based on the loudness information and a target loudness level, and adjust an output loudness level of the input audio signal based on the loudness gain. The loudness information may include information indicating a Quality Secure Histogram Index (QSHI) of the input audio signal, and the QSHI may indicate a threshold loudness level at which no cognitive sound quality impairment occurs.

[0014] The processor may compare a target loudness level of the input audio signal with the QSHI and determine the loudness gain based on the comparison.

[0015] The processor may determine the loudness gain based on the smaller of a target loudness level of the input audio signal and the QSHI.

[0016] The processor may receive a cumulative loudness level of the input audio signal and determine the loudness gain based on the cumulative loudness level of the input audio signal, the QSHI, and the target loudness level, the cumulative loudness level being a loudness level calculated based on loudness measurements obtained from a setup point in time set in a device that measures the loudness of the input audio signal.

[0017] The QSHI may be a loudness parameter calculated based on a loudness histogram of the input audio signal.

[0018] The loudness histogram may be a size histogram of short-term loudness levels by time of the input audio signal, and the short-term loudness levels may be measured in a section shorter than the entire section of the input audio signal.

[0019] The loudness histogram may be a size histogram relating to a peak value or a root-mean-square (RMS) value for each section of the input audio signal.

[0020] The QSHI may be a parameter calculated based on a predicted loudness histogram predicted from the loudness histogram of the input audio signal, and the predicted loudness histogram may be a histogram generated based on predicted loudness parameters when the input audio signal is output according to the target loudness level.

[0021] The QSHI may be greater than a cumulative loudness level of the input audio signal, the cumulative loudness level being a loudness level calculated based on loudness measurements obtained from a setup point in time set in an apparatus that measures the loudness of the input audio signal.

[0022] The processor may generate an output audio signal by adjusting an output loudness level of the input audio signal by the loudness gain, and may output the output audio signal by applying a loudness limiter to the output audio signal, which limits the loudness level of the output audio signal.

[0023] The QSHI may be a loudness parameter determined based on the number of times a limiter is activated in the audio signal processing device.

[0024] The processor can perform post processing on the input audio signal, receive post processing information indicating characteristics of post processing on the input audio signal, correct the obtained QSHI based on the post processing information, and determine the loudness gain based on the corrected QSHI.

[0025] The processor can correct the QSHI based on the post-processing information and a previously stored function.

[0026] The processor may correct the QSHI based on the post-processing information and a pre-stored look-up table, which may include information regarding QSHI correction according to post-processing characteristics.

[0027] The information on the QSHI correction may include information indicating a QSHI correction value according to a characteristic of post-processing. The processor may obtain a QSHI correction value corresponding to post-processing for the input audio signal based on the already-stored lookup table, and may add the QSHI correction value to the obtained QSHI to correct the QSHI.

[0028] The loudness gain may be a fixed gain having a fixed value over the entire duration of the input audio signal.

[0029] The loudness gain may be a time-varying gain over the time that the input audio signal is played.

[0030] The processor may generate an output audio signal by adjusting an output loudness level of the input audio signal by the loudness gain. The QSHI may be a parameter set so that a short-term loudness level of an entire section of the output audio signal is equal to or lower than a previously set level. Effect of the Invention

[0031] The apparatus and method according to an embodiment of the present invention can effectively normalize the loudness level of an audio signal when playing content including the audio signal, and can provide a user with convenience for improving sound quality and adjusting the volume.

[0032] In particular, according to an embodiment of the present invention, it is possible to control a loudness level without impairing sound quality. In addition, the audio signal processing device according to an embodiment of the present invention can provide output content having a more stable output loudness level by using loudness metadata. In addition, it is possible to perform loudness normalization close to the loudness actually perceived by a listener. [Brief description of the drawings]

[0033] [Figure 1] FIG. 2 is a diagram illustrating loudness levels that change over time while multiple contents are being played according to one embodiment of the present invention.

[0034] [Diagram 2] 1 is a schematic diagram illustrating a system including a first audio signal processing device and a second audio signal processing device according to an embodiment of the present invention.

[0035] [Diagram 3] 4 is a flow chart illustrating a method for adjusting the loudness level of an input audio signal according to one embodiment of the present invention.

[0036] [Figure 4] 2 is a block diagram specifically illustrating a method for an audio signal processing apparatus to extract loudness information of an input audio signal according to an embodiment of the present invention;

[0037] [Diagram 5]This shows the frequency response of a first-order prefilter as defined in ITU-R BS.1770-4.

[0038] [Figure 6] The frequency response of a second order prefilter is shown.

[0039] [Figure 7] FIG. 2 illustrates a method for generating loudness metadata for an input audio signal by a server according to an embodiment of the present invention.

[0040] [Figure 8] FIG. 2 illustrates a method for a client to output an input audio signal using loudness metadata according to an embodiment of the present invention.

[0041] [Figure 9] 4 is a diagram illustrating a histogram of short-term loudness magnitude of an input audio signal according to an embodiment of the present invention;

[0042] [Figure 10] 1 is a block diagram showing a system in which an audio signal processing apparatus optimizes the loudness gain of an input audio signal taking into account a target loudness level and perceived sound quality degradation according to an embodiment of the present invention;

[0043] [Figure 11] FIG. 13 is a diagram showing the loudness levels of an input audio signal over time and a fixed gain for a target loudness level. [Figure 12] FIG. 13 is a diagram showing the loudness levels of an input audio signal over time and a fixed gain for a target loudness level.

[0044] [Figure 13] FIG. 2 is a schematic diagram illustrating how the output loudness level of an input audio signal is adjusted according to one embodiment of the present disclosure. [Figure 14]FIG. 2 is a schematic diagram illustrating how the output loudness level of an input audio signal is adjusted according to one embodiment of the present disclosure.

[0045] [Figure 15] 2 is a diagram illustrating a method in which an audio signal processing apparatus according to an embodiment of the present invention acquires loudness information of an input audio signal.

[0046] [Figure 16] 2 illustrates a method for adjusting the output loudness level of an input audio signal by an audio signal processing apparatus according to an embodiment of the present invention;

[0047] [Figure 17] 4 is a diagram illustrating a method in which an audio signal processing apparatus according to an embodiment of the present invention adjusts an output loudness level of an input audio signal based on a target loudness range.

[0048] [Figure 18] 2 is a diagram illustrating a method for an audio signal processing device to measure the loudness of input content according to an embodiment of the present invention.

[0049] [Figure 19] 4 is a flowchart showing the operation of an audio signal processing device according to an embodiment of the present invention.

[0050] [Figure 20] FIG. 2 is a block diagram showing a configuration of an audio signal processing apparatus 2000 according to an embodiment of the present invention.

[0051] [Figure 21] 4 is a diagram illustrating peak values ​​for each time period of an input audio signal according to an embodiment of the present invention.

[0052] [Figure 22] 2A to 2C are diagrams illustrating a method in which an audio signal processing device according to an embodiment of the present invention adjusts the output loudness level of an input audio signal using smoothing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] Hereinafter, with reference to the accompanying drawings, an embodiment of the present invention will be described in detail so that a person having ordinary skill in the art to which the present invention belongs can easily carry out the embodiment. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. In addition, in the drawings, in order to clearly explain the present invention, parts that are not related to the description are omitted, and similar parts are given similar reference numerals throughout the specification. In addition, when a part is described as "including" a certain element, this does not mean that other elements are excluded, but means that other elements may be further included, unless otherwise specified.

[0054] The present disclosure relates to a method for an audio signal processing device to adjust an output loudness level of an input content. In the present disclosure, the input content may be a content including an audio signal. In the present disclosure, the input content may be referred to as an input audio signal. Furthermore, loudness may represent the loudness of a sound perceived by the ear. The loudness level may be a numerical value indicating loudness. For example, the loudness level may be expressed in units such as LKFS (Loudness K-Weighted relative to Full Scale) or LUFS (Loudness Unit relative to Full Scale). Furthermore, the loudness level may be expressed in units such as sone or phon.

[0055] Hereinafter, the loudness of an audio signal will be described with reference to FIG. 1. FIG. 1 is a diagram illustrating a loudness level that changes over time while a plurality of contents are reproduced according to an embodiment of the present invention. Referring to FIG. 1, an average loudness, a short-term loudness, and a loudness dynamic range that change over time are shown. The average loudness level may be a single loudness value corresponding to one content. The average loudness level may be different for each content (content1, content2, content3). In FIG. 1, the solid line represents the average loudness level for each content (content1, content2, content3). The average loudness in FIG. 1 may represent an integrated loudness. The above-mentioned integrated loudness and short-term loudness may follow the definitions of loudness standards such as ITU-R BS.1770-4, EBU R 128, EBU TECH 3341, and EBU TECH 3342.

[0056] According to an embodiment, the short-term loudness level may be a loudness level measured in a section shorter than the entire section of the input audio signal. The short-term loudness level may be a loudness measurement value for a portion of a content. In this case, the portion of the content may be a portion included in one measurement window. The audio signal processing device may obtain a plurality of short-term loudness levels for one content. Also, the average loudness level may be an average of the plurality of short-term loudness levels.

[0057] In FIG. 1, each of a plurality of contents to be reproduced and converted has different loudness characteristics. For example, when different contents are converted in a platform that provides a video providing service, advertising contents may be inserted between the converted contents. In this case, it may be difficult for the audio signal processing device to maintain a loudness level within a certain range. Also, there may be a large difference in loudness dynamic range between different contents. In such an environment, it may be difficult for the audio signal processing device to provide a loudness level within a range desired by a listener.

[0058] Specifically, when content is converted, a listener may first recognize that the loudness level for a short period changes suddenly. As a result, the listener may need to adjust the volume of the device that outputs the audio signal. Also, the listener may need to adjust the volume again to set an appropriate gain according to the average loudness while the converted content is being played. For example, when the converted content is played with a volume adjusted based on the loudness of an initial period of the converted content, a situation may occur in which the loudness level increases or decreases suddenly depending on the content characteristics. If the loudness level increases or decreases suddenly and the listener cannot understand the content, the listener may need to adjust the volume of the device that outputs the audio signal again.

[0059] For this reason, the audio signal processing device according to an embodiment of the present invention can control an output loudness level of input content to enhance convenience for a listener. Specifically, the audio signal processing device can adjust the loudness level based on a loudness gain of the input content. In this case, the audio signal processing device can use loudness metadata including loudness information of the input audio signal.

[0060] According to an embodiment of the present invention, a loudness level of an input content generated according to different standards or without a specific standard may be normalized based on a target loudness level. Here, the target loudness level may be a loudness level to be output by the audio signal processing device. For example, the target loudness level may be set by a content producer of the input content. In this case, the audio signal processing device may receive information regarding the target loudness together with the input content. Also, the target loudness level may be set to different values ​​depending on the genre of the input content. In this case, the audio signal processing device may determine the target loudness level based on the genre of the input content. The target loudness level may be set to a default value already stored in the audio signal processing device. In this case, the target loudness level may be set to a value unrelated to the input content or the genre of the input content. The audio signal processing device may adjust the output loudness level of the input content based on the target loudness level.

[0061] According to an embodiment, the audio signal processing device may obtain a loudness gain based on a relationship between a loudness level of the input content and a target loudness level. The relationship between the loudness level of the input content and the target loudness level may include a difference or ratio between the loudness level of the input content and the target loudness level.

[0062] For example, the audio signal processing device may acquire a loudness gain based on a relationship between a representative loudness level of the input content and a target loudness level. Here, the representative loudness level may be a loudness level representative of the loudness level for the entire section of the input content. The audio signal processing device may receive the representative loudness level of the input content together with the input content. Alternatively, the audio signal processing device may acquire the representative loudness level based on loudness information analyzed from the input content. In this case, the audio signal processing device may acquire the loudness information based on a loudness measurement value for the input content. In the present disclosure, the loudness information of the input audio signal may include loudness metadata converted into a metadata format.

[0063] In addition, the audio signal processing device may adjust an output loudness level of the input content based on the loudness gain. Specifically, the audio signal processing device may apply the loudness gain to the input content to obtain an output audio signal with an adjusted loudness level.

[0064] An audio signal processing device according to an embodiment of the present invention can adjust an output loudness level of an input audio signal by using loudness metadata of the input audio signal, thereby controlling the loudness level of the input content without causing a loss of sound quality of the input audio signal included in the input content.

[0065] For example, the previously set target loudness level may be greater than the representative loudness level of the input audio signal. In this case, if the input audio signal is output according to the previously set target loudness level, sound quality impairment may occur. For this reason, the audio signal processing device may acquire a loudness gain based on the loudness characteristic and the previously set target loudness. The audio signal processing device may acquire a loudness gain that does not cause sound quality impairment of the input audio signal based on the loudness characteristic. The audio signal processing device may adjust the output loudness level of the input audio signal based on the acquired loudness gain.

[0066] In this case, the audio signal processing device may acquire loudness information using loudness metadata of the input audio signal. Specifically, the audio signal processing device may receive loudness metadata of the input audio signal from a device external to the audio signal processing device. The external device may analyze loudness characteristics of the input audio signal and generate loudness metadata of the input audio signal based on the analyzed loudness characteristics. Also, the external device may transmit the loudness metadata of the input audio signal to the audio signal processing device.

[0067] Hereinafter, a method for adjusting an output loudness level of input content according to an embodiment of the present invention will be described with reference to Fig. 2. Fig. 2 is a schematic diagram showing a system 200 including a first audio signal processing device 210 and a second audio signal processing device 220 according to an embodiment of the present invention. In Fig. 2, the first audio signal processing device 210 may be a server. In Fig. 2, the second audio signal processing device 220 may be a client device.

[0068] Although Fig. 2 illustrates the sequence of operations for loudness normalization of input content as being performed by a server-client structured system, the present disclosure is not limited thereto, for example, the sequence of operations illustrated in Fig. 2 may be performed by a single audio signal processing device.

[0069] According to an embodiment of the present invention, the first audio signal processing device 210 may generate loudness metadata of an input audio signal. The first audio signal processing device 210 may transmit the generated loudness metadata to the second audio signal processing device 220 which is intended to output the input audio signal. The second audio signal processing device 220 may receive the loudness metadata from the first audio signal processing device 210. Furthermore, the second audio signal processing device 220 may adjust an output loudness level of the input audio signal based on the received loudness metadata. Specifically, the second audio signal processing device 220 may determine a loudness gain to be applied to the input audio signal based on the loudness metadata. Furthermore, the second audio signal processing device 220 may adjust the loudness level of the input audio signal based on the determined loudness gain.

[0070] Specifically, the first audio signal processing device 210 may receive input content. In the present disclosure, the input content may be an input audio signal composed of a plurality of frames. Then, the first audio signal processing device 210 may measure a loudness level of the input content. The first audio signal processing device 210 may obtain a loudness measurement value of the audio signal using a loudness filter based on a hearing scale. Specifically, the loudness filter may be at least one of an inverse filter of equal-loudness contours or a K-weighting filter that approximates the inverse filter.

[0071] For example, the first audio signal processing device 210 may apply a loudness filter to at least a portion of an already received input content to obtain a loudness measurement value. Here, the portion of the input content may be a unit time used to obtain one loudness measurement value. The portion of the input content may include at least one frame. In the present disclosure, the unit time used to obtain one loudness measurement value may be referred to as a measurement window.

[0072] The first audio signal processing device 210 may acquire loudness measurement values ​​for each measurement window for the input content. At this time, the acquired loudness measurement values ​​may be instantaneous loudness levels or short-term loudness levels depending on the length of the measurement window. The instantaneous loudness level may be a loudness measurement value measured in a time interval shorter than the short-term loudness level. For example, the length of a measurement window used to acquire one instantaneous loudness level may be 400 milliseconds (ms). Also, the length of a measurement window used to acquire one short-term loudness level may be 3 seconds. However, the present disclosure is not limited thereto. The length of a measurement window for loudness analysis may differ depending on input content. According to an embodiment, the length of the measurement window may be determined based on additional information of the input content. A method in which the audio signal processing device determines the length of a measurement window will be described later with reference to FIG. 18.

[0073] Next, the first audio signal processing device 210 may acquire loudness information of the input content based on the loudness measurement value for the input content. The loudness information may include at least one loudness measurement value for the input content. Also, the loudness information may include information calculated based on the loudness measurement value for the input content. The first audio signal processing device 210 may update the loudness information in real time. For example, the loudness information may include at least one of a cumulative loudness level, a short-term loudness level, and an instantaneous loudness level. The first audio signal processing device 210 may acquire a cumulative loudness level representing a plurality of loudness measurement values ​​accumulated from a point in time when loudness measurement for the input content is started to a current point in time.

[0074] In the present disclosure, the cumulative loudness level may represent a loudness level accumulated from a setup time point set in a device for measuring a loudness level. According to an embodiment, the cumulative loudness level may be a loudness level calculated based on loudness measurement values ​​measured from a setup time point set in the first audio signal processing device 210. For example, the cumulative loudness level may be an average loudness level calculated based on section-specific loudness measurement values ​​acquired from a setup time point. In this case, the section-specific loudness measurement value may represent any one of a short-term loudness level and an instantaneous loudness level.

[0075] According to one embodiment, the cumulative loudness level may be obtained based on an average of effective loudness measurements measured between the setup time and the current time, where the effective loudness measurement may be a loudness measurement that satisfies at least one criterion requirement among a plurality of loudness measurements measured between the setup time and the current time.

[0076] For example, the effective loudness measurement value may be a loudness measurement value having a loudness level equal to or higher than a specific level. First, the first audio signal processing device 210 may calculate a first average for loudness measurement values ​​having a loudness level equal to or higher than a first critical value among the plurality of loudness measurement values. At this time, the first critical value may be a value set based on a minimum audible loudness. Next, the first audio signal processing device 210 may calculate a second average for loudness measurement values ​​having a loudness level equal to or higher than a second critical value among the loudness measurement values ​​used in the calculation of the first average. At this time, the second critical value may be a value obtained by subtracting a previously set value from the first average. Also, the first audio signal processing device 210 may use the second average as a cumulative loudness level of the input content. Meanwhile, the first audio signal processing device 210 may re-set a setup time point for the cumulative loudness level according to a specific requirement.

[0077] Next, the first audio signal processing device 210 may generate loudness metadata based on the loudness information. For example, the first audio signal processing device 210 may remove unnecessary information from the loudness information and generate loudness metadata in a syntax form that the second audio signal processing device 220 can understand. Furthermore, the first audio signal processing device 210 may generate loudness metadata including additional information related to an input audio signal. The additional information related to the input audio signal may include at least one of information indicating the length, genre, content provider, content creator, popularity, number of views, album, and channel of the input audio signal. Thus, the first audio signal processing device 210 allows another device that outputs an input audio signal to adjust the output loudness level of the input audio signal using the additional information.

[0078] For example, the input audio signal may be a source of the same content creator as the already played audio signal. In this case, the input audio signal and the already played audio signal may have similar sound characteristics such as style / timbre. Thus, a device that outputs the input audio signal (e.g., the second audio signal processing device 220) can determine the loudness gain of the input audio signal based on the target loudness level of the already played audio signal. In this case, the second audio signal processing device 220 can use loudness metadata including additional information.

[0079] Then, the loudness metadata generated by the first audio signal processing apparatus 210 may be stored in a metadata database (hereinafter, 'DB'). The first audio signal processing apparatus 210 may receive a loudness metadata request for an input audio signal from the second audio signal processing apparatus 220. In this case, the first audio signal processing apparatus 210 may transmit the loudness metadata of the input audio signal to the second audio signal processing apparatus.

[0080] The second audio signal processing device 220 according to an embodiment of the present invention may acquire loudness information of an input audio signal from the first audio signal processing device 210. Specifically, the second audio signal processing device 220 may request loudness metadata of the input audio signal from the first audio signal processing device 210. Also, the second audio signal processing device 220 may receive the loudness metadata of the input audio signal from the first audio signal processing device 210. The second audio signal processing device 220 may acquire the loudness information of the input audio signal based on the received loudness metadata.

[0081] The second audio signal processing device 220 may acquire a loudness gain to be applied to the input content based on the loudness information. Specifically, the second audio signal processing device 220 may acquire a loudness gain based on the loudness information and a target loudness level. According to an embodiment, the second audio signal processing device 220 may acquire a loudness gain to be applied to a specific frame of the input content. The loudness gain to be applied to each frame in a specific section of the input content may be dynamically adjusted over time. The loudness gain to be applied to each frame in a section other than the specific section may be a static gain that is not dynamically adjusted. Also, the loudness gain in a specific section of the input content may be limited to a value within a specific range.

[0082] Then, the second audio signal processing device 220 may adjust an output loudness level of the input content based on the loudness gain. For example, the second audio signal processing device 220 may adjust the output loudness level by applying a loudness gain to the input content. According to an embodiment, the loudness gain may be applied to each frame constituting the input content. In this case, the second audio signal processing device 220 may adjust the output loudness level of the input content by applying the loudness gain to an audio signal corresponding to each frame. The second audio signal processing device 220 may obtain an output content whose output loudness level is adjusted according to the loudness gain from the input content. Also, the second audio signal processing device 220 may output the obtained output content. For example, the second audio signal processing device 220 may play the output content. Alternatively, the second audio signal processing device 220 may transmit the output content to a playback device via a wired / wireless interface.

[0083] Furthermore, the second audio signal processing device 220 can control the dynamic range of the adjusted output loudness level. If the output loudness level for a specific frame of the input content is outside the preset dynamic range, sound quality distortion due to clipping may occur. The second audio signal processing device 220 can control the dynamic range of the output loudness level based on the preset dynamic range. For example, the second audio signal processing device 220 can control the dynamic range of the output loudness level using processing such as a limiter and a dynamic range compressor (DRC).

[0084] Fig. 3 is a flow chart showing a method for adjusting the loudness level of an input audio signal according to an embodiment of the present invention. For convenience of explanation, Fig. 3 illustrates a series of operations for adjusting the output loudness level of an input audio signal as being performed by a single audio signal processing device, but the present disclosure is not limited thereto. For example, some of the operations illustrated in Fig. 3 may be performed by a server and others by a client.

[0085] In step S301 of Fig. 3, the audio signal processing device may perform a post-processing operation on an input audio signal. For example, the audio signal processing device may perform at least one of equalization and sound field mode operations on the input audio signal. In this case, the equalization and sound field mode performed by the audio signal processing device may be operations of a general media playback system.

[0086] In step S303, the audio signal processing device may extract loudness information of the input audio signal. According to an embodiment, when step S301 is performed, in step S303, the audio signal processing device may extract loudness information based on frequency characteristics of post-processing. The audio signal processing device may obtain band-specific loudness level information (weight of post processing, w_Proc) that changes due to post-processing based on the frequency characteristics of post-processing. Also, the audio signal processing device may extract loudness information using w_Proc.

[0087] For example, when the above-mentioned equalization is performed on the input audio signal, w_Proc may include equalization curve information in the frequency domain. The audio signal processing device may extract loudness information of the input audio signal based on the equalization curve information. When the above-mentioned sound field mode is applied to the input audio signal, w_Proc may include at least one of characteristic information of a filter used in the sound field mode and reverb information.

[0088] In another embodiment, the environment in which the input audio signal is output may be an environment in which the frequency characteristics are not uniform and the response to low frequencies is small, such as a small speaker used in a mobile phone. In this case, w_Proc may include frequency characteristic information of the output environment. Finally, the audio signal processing device may adjust the output loudness level of the input audio signal based on w_Proc. In this way, the audio signal processing device may provide an output loudness level adjustment that reflects the characteristics of the device in which the input audio signal is output.

[0089] According to an embodiment of the present disclosure, the loudness information extracted in step S303 may include at least one of an integrated loudness (L_Integ), a quality secure histogram index (QSHI), and a predicted loudness change (dL_Proc). In this case, L_Integ may comply with the ITU-R BS.1770-4 standard. Furthermore, QSHI may represent a threshold loudness level at which no perceptual sound quality damage occurs due to an output end limiter. In the present disclosure, QSHI may include a maximum target loudness (Max_TL). QSHI may be calculated based on an automatic algorithm or defined by a content creator. A specific method for obtaining QSHI will be described later with reference to FIG. 4. Furthermore, dL_Proc may be a predicted loudness change of the input audio signal after post-processing. The audio signal processing apparatus may obtain dL_Proc based on post-processing information set by a user. The audio signal processing apparatus may obtain dL_Proc based on at least one of frequency characteristics of an input audio signal and w_Proc.

[0090] In step S305, the audio signal processing device may determine a loudness gain G_target of the input audio signal. For example, the audio signal processing device may determine the loudness gain G_target based on a previously set target loudness level L_target and the loudness information extracted in step S303. In this case, the previously set target loudness level may be a value set by a user. In step S307, the audio signal processing device may apply a final loudness gain to the input audio signal post-processed in step S301 to output an output audio signal.

[0091] In this case, the output audio signal may be a signal that has passed through a limiter. For example, the audio signal processing device may generate a first output audio signal by applying a final loudness gain to the post-processed input audio signal. Also, the audio signal processing device may generate a second output audio signal by applying a limiter to the first output audio signal. Finally, the audio signal processing device may output the second output audio signal to which the limiter has been applied.

[0092] Hereinafter, a method for extracting loudness information by the audio signal processing device will be specifically described with reference to FIG. 4. FIG. 4 is a block diagram specifically illustrating a method for extracting loudness information of an input audio signal by the audio signal processing device according to an embodiment of the present invention. For convenience of description, each unit / part is described in FIG. 4 as performing each operation, but the present disclosure is not limited thereto. For example, each operation of the units / parts of the loudness information extraction unit 400 in FIG. 4 may be a series of operations performed by a processor included in the audio signal processing device.

[0093] 4, the loudness information extraction unit 400 may include a loudness measurement unit 401, a frequency-specific loudness analysis unit 402, a post-processing loudness prediction unit 403, and a QSHI extraction unit 404. The loudness information extraction unit 400 may perform the operation described in step S303 of FIG.

[0094] According to an embodiment, the loudness measurement unit 401 may obtain a loudness measurement value of an input audio signal. For example, the loudness measurement unit 401 may obtain at least one of a short-term loudness level and a cumulative loudness level of the input audio signal. Specifically, the loudness measurement unit 401 may obtain cumulative loudness information L_Integ and short-term loudness information L_ShortTerm from the input audio signal through a process such as an example in the standard ITU-R BS.1770-4.

[0095] According to an embodiment, the frequency-specific loudness analysis unit 402 may obtain a frequency-specific loudness ratio (Multi-band Weight in loudness, WLoud_MB) of the entire input audio signal. For example, the frequency-specific loudness analysis unit 402 may obtain WLoud_MB by applying a K-weighting filter to the input audio signal. The frequency-specific loudness analysis unit 402 may perform a frequency conversion on the signal to which the K-weighting filter has been applied to calculate WLoud_MB.

[0096] A specific method in which the frequency-specific loudness analysis unit 402 calculates WLoud_MB will be described below with reference to Equations 1 to 8.

[0097] [Number 1]

[0098] x_k = filter ( h_kweight, x_in )

[0099] Or,

[0100] x_k = filter ( h_pre2_kweight, filter ( h_pre1_kweight, x_in ) )

[0101] In Equation 1, x_k represents a signal obtained by applying a K-weighted filter to an input audio signal (x_in). In Equation 1, "filter(A,B)" represents an operation of filtering an input audio signal B with a filter coefficient A. In Equation 1, h_kweight may represent a single K-weighted filter. Also, h_pre2_kweight and h_pre1_kweight may represent a first pre-filter and a second pre-filter defined in ITU-R BS.1770-4, respectively. The frequency-specific loudness analysis unit 402 may filter and apply the K-weighted filter coefficients to the input audio signal. FIG. 5 represents a frequency response of a first pre-filter defined in ITU-R BS.1770-4. Also, FIG. 6 represents a frequency response of a second pre-filter.

[0102] A frame-by-frame signal of the signal x_k obtained from Equation 1 may be expressed as Equation 2. In Equation 2, x_frame[l] represents the l-th frame signal of the signal x_k, where NF represents the frame length and NH represents the hop size.

[0103] [Number 2]

[0104] x_frame[l] = x_k[ ((l-1)*NH+1) : ((l-1)*NH+NF) ]

[0105] Next, referring to Equation 3, the frequency-specific loudness analysis unit 402 may obtain xw_frame[l][-] by performing a window operation on x_frame[l]. In this case, the frequency-specific loudness analysis unit 402 may obtain xw_frame[l][-] using a rectangular window function in which all coefficients of the window function are 1. Alternatively, the frequency-specific loudness analysis unit 402 may obtain xw_frame[l][-] using various window functions such as a Hamming window function or a Hanning window function. The window operation may be an operation for frequency analysis of the input audio signal. In Equation 3, wind[n] represents the n-th coefficient of the window function, and n may be a sample number of the window. For example, when the NF is 512, the value of n may be any one of 1 to 512.

[0106] [Number 3]

[0107] xw_frame[l][n] = x_frame[l][n] * wind[n] for n=1, 2, …, NF

[0108] Furthermore, the frequency-specific loudness analysis unit 402 may perform a Discrete Fourier Transform (DFT) on xw_frame[l][-]. The frequency domain signal (XW_frame[l]) that is discrete Fourier transformed from xw_frame[l][-] may be expressed as in Equation 4. In Equation 4, DFT{x} represents the discrete Fourier transform of the time domain signal 'x'.

[0109] [Number 4]

[0110] XW_frame[l] = DFT { xw_frame[l][1:NF]}

[0111] Next, referring to Equation 5, the frequency-specific loudness analysis unit 402 can obtain the power for each frequency bin of the converted frequency signal XW_frame[l]. In Equation 5, P_frame_bin[l][k] represents the power in the k-th frequency bin of the l-th frame. Also, conj(x) represents the conjugation function of 'x'.

[0112] [Number 5]

[0113] P_frame_bin[l][k] = XW_frame[l][k] * conj(XW_frame[l][k]) for k=1, 2, …, NF

[0114] Next, referring to Equation 6, the frequency-specific loudness analysis unit 402 may map P_frame_bin[l][k] to a previously set frequency band and obtain the power of each frequency band of the l-th frame (P_frame_band[l][b]). In Equation 6, band[b] represents the index of the start frequency bin of the b-frequency band. That is, the frequency-specific loudness analysis unit 402 may obtain the power of each frequency band by summing the power of each frequency bin from band[b] to band[b+1]-1. In Equation 6, sum_{y}(x) may represent the sum of the function 'x' index having index k as a factor. In this case, 'y' may represent the range of indexes for this calculation.

[0115] [Number 6]

[0116] P_frame_band[l][b]

[0117] = sum_{k from band[b] to band[b+1]-1} (P_frame_bin[l][k])

[0118] Referring to Equation 7, the frequency-specific loudness analysis unit 402 can obtain the frequency band-specific power (P_band[b]) of the entire section of the input audio signal based on the frequency band-specific power (P_frame_band[l][b]) of the l-th frame. The frequency-specific loudness analysis unit 402 can obtain the frequency band-specific power (P_band[b]) of the entire section of the input audio signal by adding up the frequency band-specific powers (P_frame_band[l][b]) obtained for each frame for the same frequency bands. In Equation 7, NumberOfFrames represents the number of all frames. Also, l representing a frame index is defined within the range from 1 to NumberOfFrames.

[0119] [Number 7]

[0120] P_band[b] = sum_{l from 1 to NumberOfFrames} (P_frame_band[l][b])

[0121] Next, referring to Equation 8, the frequency-specific loudness analysis unit 402 can obtain a frequency band-specific loudness ratio (WLoud_MB[b]) based on the frequency band-specific power (P_band[b]). Specifically, the frequency-specific loudness analysis unit 402 can normalize the specific frequency band-specific power (P_band[b]) based on the sum of all frequency band-specific powers. In Equation 8, NumberOfBands represents the total number of divided frequency bands. Also, b representing a band index is defined within the range from 1 to NumberOfBands.

[0122] [Number 8]

[0123] WLoud_MB[b] = P_band[b] / [sum_{b from 1 to NumberOfBands} (P_band[b])]

[0124] WLoud_MB[b] calculated from Equation 8 represents a ratio of cumulative loudness levels of the input audio signal for each frequency band. For example, the input audio signal may be a two-band signal, the cumulative loudness level of the input audio signal may be L_Integ=-20LKFS, and WLoud_MB

[10] =0.8, WLoud_MB[1]=0.2. In this case, the loudness level of the first frequency band of the input audio signal may be predicted to be -20+10*log10(0.8)=-20.97LKFS, and the loudness level of the second frequency band may be predicted to be -20+10*log10(0.2)=-26.99LKFS.

[0125] According to an embodiment, the post-processing loudness prediction unit 403 may obtain a loudness change prediction value based on at least one of the band-specific loudness level information (w_Proc) that changes due to post-processing and the frequency-specific loudness ratio (WLoud_MB) of the entire input audio signal.

[0126] At this time, the post-processing loudness prediction unit 403 can use the frequency-specific loudness ratio (WLoud_MB) of the entire input audio signal acquired from the frequency-specific loudness analysis unit 402. In addition, the band-specific loudness level information (w_Proc) that changes due to post-processing may be acquired according to the characteristics of post-processing for the input audio signal. The characteristics of post-processing for the input audio signal may be determined based on information input by a user.

[0127] Specifically, the equalization set by the user may be applied to the input audio signal, and the frequency band gain of the equalization may be set to w_ProcBand_dB in decibel units for each of the NumberOfBands frequency bands, and the total gain of the equalization may be set to w_ProcGain_dB. In this case, the frequency-specific loudness analysis unit 402 may obtain the loudness ratio for each frequency band based on the frequency band gain (w_ProcBand_dB) and the total gain (w_ProcGain_dB). The method of calculation by the frequency-specific loudness analysis unit 402 to obtain the loudness ratio for each frequency band may be expressed as Equation 9.

[0128] [Number 9]

[0129] w_Proc[b] = 10^((w_ProcBand_dB[b] + 0.5*w_ProcGain_dB) / 10)

[0130] for 1= <b=<NumberOfBands

[0131] Moreover, the method in which the post-processing loudness prediction unit 403 obtains the loudness change prediction value dL_Proc can be expressed as in Equation 10.

[0132] [Number 10]

[0133] dL_Proc = 10 * log10 ( sum_{b from 1 to NumberOfBands} (WLoud_MB[b] * w_Proc[b]) )

[0134] According to an embodiment, the QSHI extraction unit 404 can extract a quality assurance histogram index QSHI based on the short section loudness information L_ShortTerm. As described above, the quality assurance histogram index (hereinafter, referred to as 'QSHI') may be a threshold loudness level at which no perceptual sound quality impairment occurs. The QSHI extraction unit 404 can acquire the QSHI based on the short section loudness information L_ShortTerm acquired from the loudness measurement unit 401.

[0135] For example, the QSHI extraction unit 404 may acquire the QSHI by analyzing the short section loudness information L_ShortTerm. In this case, the short section loudness information L_ShortTerm may include one or more short section loudness levels of the input audio signal. Specifically, the QSHI extraction unit 404 may acquire a short section loudness magnitude histogram of the input audio signal based on the one or more short section loudness levels. In addition, the QSHI extraction unit 404 may acquire the QSHI of the input audio signal based on the acquired short section loudness magnitude histogram.

[0136] Hereinafter, a specific method in which the QSHI extraction unit 404 extracts the QSHI from the short section loudness information L_ShortTerm of the input audio signal will be described with reference to Equations 11 and 12. In Equation 11, L_ShortTerm_Sorted represents information in which one or more short section loudness levels included in the short section loudness information L_ShortTerm of the input audio signal are sorted in order of magnitude. For example, the QSHI extraction unit 404 can sort one or more short section loudness levels in descending order.

[0137] [Number 11]

[0138] L_ShortTerm_Sorted = sort ( L_ShortTerm, 'descending' )

[0139] Furthermore, the QSHI extraction unit 404 may acquire a loudness level corresponding to a previously set index among one or more short section loudness levels of the input audio signal based on L_ShortTerm_Sorted. In Equation 12, EffectiveIndex may represent a previously set effective index. Specifically, the previously set effective index (EffectiveIndex) may indicate a short section loudness level in a previously set order in order of magnitude among one or more short section loudness levels of the input audio signal. That is, the QSHI extraction unit 404 may acquire a short section loudness level that is the EffectiveIndex-th largest among one or more short section loudness levels of the input audio signal. In this case, the short section loudness level that is the EffectiveIndex-th largest among one or more short section loudness levels of the input audio signal may be referred to as an effective short section loudness level (L_ShortTerm_Effective) of the input audio signal.

[0140] [Number 12]

[0141] L_ShortTerm_Effective = L_ShortTerm_Sorted[EffectiveIndex]

[0142] Next, the QSHI extraction unit 404 can obtain the QSHI based on at least one of the effective short-term loudness level (L_ShortTerm_Effective) and the accumulated loudness level of the input audio signal, and the QSHI may be greater than or equal to the accumulated loudness level.

[0143] Furthermore, the QSHI extraction unit 404 may acquire an effective short-term loudness level (L_ShortTerm_Effective_Shift) to be changed when the input audio signal is output according to a previously set target loudness level. Specifically, the QSHI extraction unit 404 may predict the short-term loudness information (L_ShortTerm_Shft) to be changed based on the short-term loudness information L_ShortTerm of the input audio signal. At this time, the short-term loudness information (L_ShortTerm_Shft) to be changed may include one or more short-term loudness levels to be changed when the input audio signal is output according to a previously set target loudness level. In this case, the QSHI extraction unit 404 may acquire the QSHI based on the acquired L_ShortTerm_Effective_Shift. For example, the QSHI may be a target loudness maximum allowable value when the short-term loudness level is restricted to be equal to or less than a threshold value of the L_ShortTerm_Effective_Shift[EffectiveIndex] short-term loudness level.

[0144] For example, L_ShortTerm_Effective_Shift of the input audio signal may be used as a short-term loudness level threshold (L_Threshold). The QSHI extraction unit 404 may correct the target loudness maximum allowable value based on L_ShortTerm_Effective_Shift. The QSHI extraction unit 404 may use the corrected target loudness maximum allowable value as the QSHI value. Alternatively, the QSHI extraction unit 404 may select the larger value of the target loudness maximum allowable value corrected in the above manner and the accumulated loudness of the input audio signal as the QSHI value.

[0145] According to the above method, the audio signal processing device can effectively prevent degradation of sound quality of the input audio signal caused by the limiter, since the sound quality of the input audio signal may be degraded by the limiter in a portion where the volume is set relatively high among the entire section of the input audio signal.

[0146] According to an embodiment, QSHI may be a value set such that the number of short section loudness levels greater than a specific value among one or more short section loudness levels of an input audio signal is smaller than EffectiveIndex. In this case, EffectiveIndex may be a value determined based on the characteristics of a limiter of the audio signal processing device. For example, EffectiveIndex may be changed depending on the degree of sound quality degradation caused by the operation of the limiter. Furthermore, the short section loudness threshold (L_Threshold) may be a value determined based on the characteristics of a limiter of the audio signal processing device. For example, the short section loudness threshold (L_Threshold) may be changed depending on the degree of sound quality degradation caused by the operation of the limiter.

[0147] According to a specific embodiment, the input audio signal may have a relatively large dynamic range. For example, the cumulative loudness level of the input audio signal may be L_Integ=-24LKFS, and the effective short-term loudness level may be extracted as L_ShortTerm_Effective=-10LKFS. In this case, when EffectiveIndex=10 and the short-term loudness threshold=-7LKFS are set, the QSHI may be calculated as -21LKFS.

[0148] In the above embodiment, the QSHI of the input audio signal is extracted based on the short-term loudness magnitude histogram, but the present disclosure is not limited thereto. For example, the QSHI of the input audio signal may be defined as a value arbitrarily set by a creator of the content including the input audio signal or an operator of the sound system that outputs the input audio signal. In addition, the audio signal processing device may obtain the QSHI by performing a histogram analysis on at least one of the peak envelope and RMS of the input audio signal in addition to the short-term loudness level.

[0149] According to an embodiment, the QSHI of the input audio signal may change according to a change in the short-term loudness magnitude histogram. For example, the above-mentioned short-term loudness magnitude histogram may change according to the presence or absence of post-processing determined by a user's input. In this case, the QSHI of the input audio signal may be changed to another value based on a previously set table. Alternatively, the QSHI of the input audio signal may be changed to a value calculated based on the characteristics of the post-processing.

[0150] Further, a method for an audio signal processing device according to an embodiment of the present disclosure to determine a loudness gain of an input audio signal based on the loudness information described above will be described. Equation 13 represents a changed cumulative loudness level (L_IntegProc) of an input audio signal when a post-processing process is performed on the input audio signal. The audio signal processing device may obtain a changed cumulative loudness level (L_IntegProc) of the input audio signal based on a loudness change prediction value dL_Proc due to post-processing. Referring to Equation 13, the audio signal processing device may obtain a changed cumulative loudness level (L_IntegProc) by adding the loudness change prediction value dL_Proc due to post-processing to the cumulative loudness level of the input audio signal.

[0151] [Number 13]

[0152] L_IntegProc = L_Integ + dL_Proc

[0153] The audio signal processing device can calculate a loudness gain for adjusting the output loudness level based on the above-mentioned QSHI, a previously set target loudness level (L_Target), and an accumulated loudness level changed by post-processing.

[0154] In the above-described embodiment, the target loudness level (L_Target) may be a value set by a user. However, the present disclosure is not limited thereto. For example, the previously set target loudness level (L_Target) may be a default value provided by a playback system that outputs an input audio signal. Or, the previously set target loudness level (L_Target) may be a value set based on a playback environment that outputs an input audio signal. The audio signal processing device may apply a loudness gain (G_Target) to a first intermediate audio signal post-processed from an input audio signal. For practical convenience of implementation, the post-processing process may be performed after the loudness gain (G_Target) is applied to the input audio signal before the post-processing. Also, the audio signal processing device may pass the second intermediate audio signal to which the loudness gain (G_Target) has been applied through a limiter and output the signal.

[0155] Meanwhile, a multimedia streaming service is a method that is currently widely used in the media market. A system for providing a multimedia streaming service may generally include a server that stores content to be streamed, and a user device (i.e., a client). At this time, the multimedia streaming service may be provided in the form of in-application playback or in-web playback on the client side. Each of the server and the client may be an audio signal processing device that performs the operations described in the present disclosure. In such a server-client structure, the server may perform input content analysis to provide loudness information. Also, the client may adjust an output loudness level of the input content based on the loudness information provided by the server. Specifically, the server may transmit loudness metadata including loudness information of an input audio signal to the client. The client may receive the loudness metadata of the input audio signal from the server. Also, the client may obtain a loudness gain to be applied to the input audio signal based on the loudness metadata of the input audio signal.

[0156] FIG. 7 is a diagram illustrating a method in which a server according to an embodiment of the present invention generates loudness metadata of an input audio signal. The server according to an embodiment of the present invention may encode an input audio signal and generate and / or output an audio stream. The server according to an embodiment of the present invention may extract loudness information of an input audio signal. For example, the server of FIG. 7 may perform the operation described with reference to the loudness information extraction (step S303) of FIG. 3 and the operation described with reference to the loudness information extraction unit 400 of FIG. 4. The server may also generate loudness metadata including the extracted loudness information. The server may output the generated loudness metadata to an external device. For example, the server may transmit the generated loudness metadata to a client in the form of a metadata stream.

[0157] 8 is a diagram illustrating a method in which a client according to an embodiment of the present invention outputs an input audio signal using loudness metadata. The client according to an embodiment of the present invention may receive an audio stream. The client may also obtain an input audio signal by decoding the received audio stream. The client may perform a post-processing process on the input audio signal. In this case, whether or not to perform the post-processing process and the characteristics thereof may be determined based on an input received from a user or a setting value already stored in the system.

[0158] A client according to an embodiment of the present invention may determine a loudness gain of an input audio signal based on loudness metadata of the input audio signal. For example, the client may receive loudness metadata in the form of a metadata stream. The client may parse the loudness metadata of the input audio signal to obtain loudness information of the input audio signal. Specifically, the client may obtain at least one of WLoud_MB, L_Integ, and QSHI described above in FIG. 3 and FIG. 4 from the loudness metadata of the input audio signal. The client may determine a loudness gain of the input audio signal based on the obtained loudness information. The client may adjust an output loudness level by applying a loudness gain to the input audio signal. The client may generate an output audio signal by applying a limiter to the intermediate audio signal whose output loudness level has been adjusted. Also, the client may output the output audio signal.

[0159] According to one embodiment, the client of FIG. 8 can perform the operations described with reference to the post-processing (step S301), loudness gain determination (step S305), and loudness gain application (step S307) of FIG. 3, and the operations described with reference to the post-processing loudness prediction unit 403 of FIG. 4.

[0160] Meanwhile, music content may have various loudness levels depending on the era and / or genre. For example, the cumulative loudness level of classical music is relatively low to provide a wide dynamic range, while the cumulative loudness level of popular music from the 2000s is relatively high. Specifically, the cumulative loudness level of popular music from the 2000s may be -13 to -8 LKFS, and the cumulative loudness level of a quiet movement of classical music may be about -30 LKFS.

[0161] When determining the target loudness level, -23 to -24 LKFS defined in the broadcasting standard can be utilized. However, this may not provide sufficient volume against external noise in a noisy environment such as a subway. For this reason, an audio signal processing device according to an embodiment of the present invention can determine a different target loudness level depending on the reproduction environment. When the target loudness level of popular music of the 2000s is set to -10, the volume of the popular music of the 2000s may not change significantly. In contrast, when the target loudness level of music having a relatively low integrated loudness level such as classical music or music of the 1970s to 1980s is set to -10, the volume may change significantly.

[0162] 9 is a diagram illustrating a short-term loudness magnitude histogram of an input audio signal according to an embodiment of the present invention. In the embodiment illustrated in FIG. 9, the genre of the input audio signal may be classical. In addition, in the embodiment illustrated in FIG. 9, the cumulative loudness of the input audio signal may be -21 LKFS. For example, the target loudness level of the input audio signal may be L_Target=-10 LKFS. In this case, the short-term loudness magnitude histogram shifts +11 LKFS to the right. At this time, a section having a short-term loudness level greater than -7 LKFS occurs.

[0163] According to an embodiment, sound quality degradation due to the limiter may occur in a section having a short-term loudness level greater than -7LKFS. For this reason, the audio signal processing device according to an embodiment of the present invention may perform loudness normalization of an input audio signal based on QSHI as described above. In this case, although loudness normalization performance may be relatively reduced, a best-effort method may be used that performs the most aggressive matching within a range that prevents sound quality degradation.

[0164] According to an embodiment of the present invention, the audio signal processing device can use a loudness gain correction method that most closely approximates a target loudness level based on loudness information of an input audio signal. By using the method, the audio signal processing device can provide equalization without changing the loudness level.

[0165] Equalization refers to adjusting the frequency-specific energy of an input audio signal to provide a tone color desired by a user. In this case, a phenomenon in which the overall energy increases depending on the degree of adjustment of the input audio signal may occur. In this case, the input audio signal may be clipped. In addition, a limiter may cause sound quality degradation compared to the input audio signal. For this reason, the audio signal processing device according to an embodiment of the present invention may set the previously set target loudness level (L_Target), cumulative loudness level (L_Integ), and QSHI to the same arbitrary value. In this case, the loudness gain (G_Target) of the input audio signal may be expressed as in Equation 14. That is, the audio signal processing device may obtain a linear loudness gain (G_Target). This is because the target loudness level (L_Target), cumulative loudness level (L_Integ), and QSHI are offset by each other.

[0166] [Number 14]

[0167] G_Target = power ( 10, -dL_Proc) / 20

[0168] The audio signal processing device may apply the loudness gain (G_Target) of Equation 14 to the input audio signal. The audio signal processing device may provide an output loudness level equal to the loudness level of the input audio signal by compensating for a loudness change due to post-processing. The audio signal processing device may maintain the loudness level of the input audio signal by compensating for a loudness change due to post-processing. The audio signal processing device may set the loudness level of the intermediate audio signal to be equal to the loudness level of the input audio signal by using a predicted loudness change value due to post-processing. In this case, the intermediate audio signal may be a signal post-processed from the input audio signal. This means that the audio signal processing device provides an input audio signal having a tone changed in comparison with the input audio signal by the post-processing process, but with the same loudness level as the original input audio signal. Meanwhile, the predicted loudness change value due to post-processing may be obtained by the method described above in FIG. 3 and FIG. 4. The predicted loudness change value due to post-processing may be obtained based on a WLoud_MB provided by analysis or a WLoud_MB based on a content characteristic.

[0169] 10 is a block diagram showing a system in which an audio signal processing device optimizes a loudness gain of an input audio signal in consideration of a target loudness level and perceived sound quality degradation according to an embodiment of the present invention. The audio signal processing device can determine a target loudness gain that a dynamic processor can accept based on the target loudness level and loudness information of the input audio signal. Here, the dynamic processor can represent a processing process of clipping a signal according to a loudness level, like the above-mentioned limiter or compressor. The loudness information of the input audio signal can include at least one of a cumulative loudness level, a short-term loudness level, an instantaneous loudness level, a sample peak, a true peak, a loudness range, and RMS (root-mean-square).

[0170] A specific example in which the audio signal processing device determines the loudness gain of an input audio signal will be described below. In one example, the maximum value of the target loudness level that can be set by the user may be -10LKFS, and the cumulative loudness of the input audio signal may be -22LKFS. In addition, the short-term loudness level corresponding to the 10th of the multiple short-term loudness levels of the input audio signal may be -18LKFS. In this case, the short-term loudness level corresponding to the 10th may be a specific example of the effective short-term loudness level (L_ShortTerm_Effective) described with reference to the QSHI extraction unit 404 of FIG. 4. That is, -18LKFS may be used as an index for determining whether or not there is sound quality degradation due to DRC. When the maximum value of the target loudness level is -10LKFS, the maximum amplification amount may be 12 LU (Loudness Unit). In this case, the audio signal processing device can acquire the QSHI based on the 10th short-term loudness level amplified by the maximum amplification amount.

[0171] The audio signal processing device may compare a target loudness level already set by a user with the QSHI. The audio signal processing device may determine a loudness gain of an input audio signal based on a comparison result. For example, the audio signal processing device may determine a loudness gain of an input audio signal based on a relatively smaller value of the target loudness level already set and the QSHI. In the above-described embodiment, the short-term loudness level for obtaining an index for determining the presence or absence of DRC sound quality degradation is selected as the top 10 in descending order, but the present disclosure is not limited thereto. In addition, the audio signal processing device may perform a histogram analysis on at least one of the peak value and RMS of a signal in addition to the short-term loudness level to obtain the QSHI.

[0172] 11 and 12 are diagrams illustrating the loudness levels of time-dependent input audio signals and fixed gains for the target loudness level. FIG. 11 illustrates a fixed gain for adjusting the loudness level of a first input audio signal having a loudness distribution smaller than the target loudness level to the target loudness level. In this case, the first input audio signal may be clipped in a section larger than 0 dBFS, causing excessive timbre distortion. Thus, there is a limit to the loudness level adjustment method using a fixed gain in order to obtain a value close to the target loudness level. For this reason, the audio signal processing device may apply a gain smaller than the fixed gain value to the first input, section (2) and section (4) of the audio signal.

[0173] 12, the second input audio signal has a larger dynamic range than the first input audio signal of FIG 11. As a result, when the audio signal processing device applies a fixed gain for a target loudness level to the second input audio signal, some sections may have a relatively small loudness level. Therefore, the audio signal processing device may apply a gain larger than the fixed gain value to sections (1) and (3) of the second input audio signal.

[0174] According to a further embodiment, the audio signal processing device may apply a gain boost. For example, the audio signal processing device may acquire a target loudness range. The audio signal processing device may set an additional gain for each section of the input audio signal based on the acquired target loudness range. Specifically, the audio signal processing device may apply the set additional gain to a section having a loudness level outside the target loudness range among all time sections of the input audio signal.

[0175] As described above, an audio signal processing device according to an embodiment of the present disclosure may adjust an output loudness level of an input audio signal by applying a gain that varies over time to the input audio signal. The audio signal processing device may adjust an output loudness level of the input audio signal based on loudness metadata of the input audio signal. In this case, the loudness metadata of the input audio signal may include information that changes over time. In order to apply a gain that varies over time, the audio signal processing device may normalize an output loudness level of the input audio signal according to a target loudness level and a target loudness range by referring to metadata that varies over time. As a result, in the present disclosure, the audio signal processing device may solve the above-mentioned problem when applying a fixed gain to an input audio signal for loudness normalization to perform compensation.

[0176] 13 and 14 are schematic diagrams illustrating a method for adjusting an output loudness level of an input audio signal according to an embodiment of the present disclosure. FIG. 13 illustrates an embodiment in which loudness information of an input audio signal is extracted and an output loudness level of the input audio signal is adjusted in a single audio signal processing device. In this case, the audio signal processing device can measure the loudness level of the input audio signal. The audio signal processing device can obtain the loudness information of the input content in a loudness measurement value. A method in which the audio signal processing device measures the loudness level of an input audio signal in real time will be specifically described in FIG. 19.

[0177] FIG. 14 illustrates the server-client structure described above with reference to FIGS. 7 and 8. First, the server may analyze an input audio signal to extract loudness information of the input audio signal. Also, the server may convert the loudness information of the input audio signal into a metadata format to generate loudness metadata. Next, the client may receive the input audio signal and receive the loudness metadata of the input audio signal separately from the input audio signal. Also, the client may parse the loudness metadata to obtain loudness information used to adjust an output loudness level of the input audio signal. Also, the client may obtain a loudness gain of the input audio signal based on the loudness information and a previously set target loudness level. The client may adjust the output loudness level of the input audio signal based on the loudness gain of the input audio signal.

[0178] Fig. 15 is a diagram illustrating a method for an audio signal processing device according to an embodiment of the present invention to acquire loudness information of an input audio signal. The audio signal processing device may acquire loudness information by analyzing an input audio signal. For example, the method of Fig. 15 may be performed by the server of Fig. 7 described above. The audio signal processing device may output the loudness information in the form of loudness metadata.

[0179] According to an embodiment, the loudness information may include static loudness metadata and dynamic loudness metadata. The static loudness metadata may include at least one static loudness parameter. For example, the static loudness metadata may include at least one of a cumulative loudness level of the input audio signal, a Max. Sample Peak, a Loudness Range (LRA), a Peak to Loudness Range (PLR), an Album Integrated Loudness, a Relative Threshold, a Min. Momentary Loudness, a Max. Momentary Loudness, and a Sample Per Frame.

[0180] The audio signal processing device may obtain static loudness metadata of an input audio signal. Specifically, the audio signal processing device may measure at least one of an instantaneous loudness level of the input audio signal and a short-term loudness level of the input audio signal using a loudness filter based on a hearing scale. The audio signal processing device may generate static loudness metadata including at least one static loudness parameter.

[0181] The dynamic loudness metadata may indicate loudness information that changes with time. The dynamic loudness metadata may include at least one dynamic loudness parameter. For example, the dynamic loudness metadata may include at least one of a short-term loudness level and a peak value (Peak Envelope) for each time of the input audio signal. A method for the audio signal processing device to obtain the peak value will be specifically described with reference to FIG. 21.

[0182] According to an embodiment, the audio signal processing device may acquire dynamic loudness metadata of an input audio signal. For example, the audio signal processing device may acquire a short-term loudness measurement value for a specific section of the input audio signal. The audio signal processing device may acquire a peak value of the input audio signal for the section. The audio signal processing device may generate dynamic loudness metadata including at least one dynamic loudness parameter. The audio signal processing device may also correct time delays or advances of dynamic loudness parameters such as the short-term loudness measurement value and the peak value. For example, the audio signal processing device may shift the dynamic loudness parameter. This will be described in detail with reference to FIG. 21.

[0183] The audio signal processing device may acquire short-term loudness levels for past sample values ​​and subsequently input sample values ​​based on a specific time point. As a result, the audio signal processing device may more stably control the loudness level with respect to loudness changes of an input audio signal. For example, the audio signal processing device may shift a time reference value of an already acquired dynamic loudness parameter to acquire short-term loudness levels for past sample values ​​and subsequently input sample values. In addition, the audio signal processing device may acquire short-term loudness levels for past sample values ​​and subsequently input sample values ​​using a buffer. In this case, the audio signal processing device may set a sufficient look-ahead time.

[0184] FIG. 16 is a diagram illustrating a method in which an audio signal processing device according to an embodiment of the present invention adjusts an output loudness level of an input audio signal. The audio signal processing device may acquire a loudness gain of an input audio signal based on a target loudness level and loudness metadata of the input audio signal. Specifically, the audio signal processing device may calculate a gain parameter based on the target loudness level and the static loudness metadata. The audio signal processing device may acquire a loudness gain to be applied to a specific frame of the input audio signal based on the calculated gain parameter and the dynamic loudness metadata. For example, the audio signal processing device may parse the dynamic loudness metadata and acquire at least one of a short-term loudness level and a peak value corresponding to the frame. The audio signal processing device may acquire a loudness gain to be applied to the frame based on at least one of a short-term loudness level and a peak value corresponding to the frame. Specifically, the audio signal processing device may acquire a loudness gain to be applied to the frame based on the calculated gain parameter and the short-term loudness level corresponding to the frame. In this case, the loudness gain to be applied to the frame may be limited so that clipping due to the loudness level does not occur in the frame. The audio signal processing device may correct a loudness gain applied to a frame based on a peak value so that clipping due to a loudness level does not occur in the frame. The audio signal processing device may generate an intermediate audio signal by applying a final loudness gain to an input audio signal. Also, the audio signal processing device may generate an output audio signal by applying a limiter to the intermediate audio signal. The audio signal processing device may output an output audio signal. According to a further embodiment, when a difference in frame-by-frame loudness gain between adjacent frames is equal to or greater than a pre-set magnitude, the audio signal processing device may correct the frame-by-frame loudness gain.At this time, the audio signal processing device may adjust the loudness gain to change gradually using a smoothing method. As a result, the audio signal processing device may prevent tone distortion caused by changes in loudness gain for each frame and volume pumping caused by a sudden large change in level. A method for smoothing the loudness gain by the audio signal processing device will be described in detail with reference to FIG. 22.

[0185] 17 is a diagram illustrating a method in which an audio signal processing device according to an embodiment of the present invention adjusts an output loudness level of an input audio signal based on a target loudness range. The audio signal processing device may further consider the target loudness range in the process of calculating the gain parameters of FIG. 16 described above. As described in FIG. 12, the target loudness range may be narrower than the dynamic range of the input audio signal. Depending on the environment, when listening to video / audio at a low volume or listening to music in a noisy environment such as a subway or a road, it is necessary to reduce the dynamic range of the input audio signal before reproduction.

[0186] Thereby, the audio signal processing device may calculate a gain parameter of the input audio signal based on a target loudness range of the input audio signal. At this time, the gain parameter may include a gain ratio used for loudness compression. The audio signal processing device may apply an additional boost gain to a frame having a short-term loudness smaller than a previously set magnitude among a plurality of frames included in the input audio signal based on the gain ratio. The audio signal processing device may apply an additional cut gain to a frame having a short-term loudness larger than a previously set magnitude among a plurality of frames included in the input audio signal based on the gain ratio. Thereby, the audio signal processing device may adjust an output loudness level of an entire section of the input audio signal to be close to a target loudness level.

[0187] According to an additional embodiment, the audio signal processing device may perform loudness normalization for each time interval based on loudness parameters measured differently for each time interval. Specifically, the audio signal processing device may determine a loudness gain (G_loud) for each time interval of the input audio signal based on a target loudness level (L_T), an accumulated loudness level (L_I), a short-term loudness level (L_S), a relative threshold (L_Rel), a noise floor level (L_Noise), and a peak value (P). Here, L_Rel may be a value obtained by adding a previously set value to an average of dynamic loudness parameters effective in the entire interval of the input audio signal. In this case, the previously set value may be -20LU. Also, the dynamic loudness parameter may be an instantaneous loudness level or a short-term loudness level.

[0188] For example, L_Rel may be a value calculated based on an average of short section loudness levels having a value greater than at least the effective loudness level among the short section loudness levels of each section of the input audio signal. L_Rel may be a value calculated based on an average of instantaneous loudness levels having a value greater than at least the effective loudness level among the instantaneous loudness levels of each section of the input audio signal. Here, the effective loudness level may be a value set based on a loudness level that is difficult to perceive auditorily. The effective loudness level may be a value set based on the loudness level of an audio signal in which sound is almost absent. For example, the effective loudness level may be a value set based on -70LKFS.

[0189] Furthermore, L_Noise may be a value calculated based on at least one of the loudness level of an interval where there is almost no sound in the input audio signal or the loudness level of an interval corresponding to a very low level of background noise in the input audio signal.

[0190] According to an embodiment, each of L_T, L_I, L_S, L_Rel, L_Noise and P may be obtained from the loudness metadata described above. Also, the time interval may include a frame. In the above embodiment, the short-term loudness level (L_S) may be replaced with a loudness representative value representing a specific time interval. For example, the short-term loudness level (L_S) may be replaced with an instantaneous loudness level of an input audio signal. A method in which the audio signal processing device obtains a loudness gain (G_loud) for each time interval based on L_T, L_I, L_S, L_Rel, L_Noise and P is expressed as Equation 16 below.

[0191] [Number 16]

[0192]

number

[0193] In Equation 16, r_1 and r_2 may represent loudness compression ratios for controlling the dynamic range of the output audio signal with respect to the input audio signal. r_1 may be a loudness compression ratio used to obtain a loudness gain for a section in which the input loudness level of the input audio signal is smaller than at least the cumulative loudness level. r_1 may be set based on at least one of LRA, PLR, or instantaneous loudness maximum value indicating the loudness range of the input audio signal. r_1 may be any constant between 0 and 1. r_2 may be a compression ratio used to obtain a loudness gain for a section in which the input loudness level of the input audio signal is smaller than the cumulative loudness level and the input loudness level is smaller than L_Rel. In this case, r_2 may be set to a value at least smaller than r_1 in order to minimize boosting of noise components. The audio signal processing device may smooth G_loud[n] and apply it to the input audio signal. Furthermore, clippingThreshold may represent a maximum allowable sample peak value. ClippingThreshold may be a value set based on at least one of the above-mentioned QSHI, maximum true peak, and maximum sample peak value. For example, clippingThreshold may be the same value as QSHI. Alternatively, clippingThreshold may be a value arbitrarily set in the audio signal processing device or audio providing system.

[0194] Hereinafter, a method for an audio signal processing device according to an embodiment of the present invention to acquire a loudness measurement value will be described in detail with reference to FIG. 18. FIG. 18 is a diagram illustrating a method for an audio signal processing device to measure loudness of input content according to an embodiment of the present invention. According to an embodiment, the audio signal processing device may measure the loudness of the input content based on the above-mentioned measurement window. Also, the audio signal processing device may acquire a loudness measurement value for each measurement window of the input content. The audio signal processing device may acquire loudness information based on the loudness measurement value for each measurement window.

[0195] In the embodiment of FIG. 18, the audio signal processing device may obtain a measurement value for each measurement window based on the length of the measurement window 801. At this time, the length of the measurement window 801 may be a default value already stored in the audio signal processing device. According to an embodiment of the present invention, the length of the measurement window 801 may vary depending on the input content. For example, the audio signal processing device may obtain the length of the measurement window corresponding to the input content based on additional information of the input content. In the embodiment of FIG. 18, the length of the measurement window corresponding to the input content may be 400 ms. The audio signal processing device may obtain a loudness measurement value corresponding to a specific 400 ms long section in the entire section of the input content.

[0196] According to an embodiment, the length of the measurement window may be obtained based on the additional information. For example, the length of the measurement window may be obtained based on the loudness range of the input content. Here, the loudness range may be a value representing a loudness level distribution for the entire section of the content. The loudness range may be displayed using a unit indicating a relative measurement amount such as LU. The audio signal processing device may obtain information regarding the loudness range of the input content from the additional information. Next, the audio signal processing device may determine the length of the measurement window based on the loudness range of the input content. At this time, the length of the measurement window of the input content may be set to a value shorter than the measurement window length of another content having a loudness range width wider than the loudness range of the input content. For example, when the loudness range of the first input content is larger than the loudness range of the second input content, the length of the measurement window for the first input content may be longer than the length of the measurement window for the second input content.

[0197] Furthermore, the audio signal processing device may acquire loudness measurement values ​​for each measurement window according to a measurement period for acquiring a measurement value for the input content. In the present disclosure, the measurement period may represent a time distance over which the measurement window moves. Referring to FIG. 18, the first measurement value 802 may be a loudness measurement value corresponding to a section (300 ms to 700 ms) based on the time point at which the input content starts to be played. Furthermore, the second measurement value 803 may be a loudness measurement value corresponding to a section (400 ms to 800 ms) based on the time point at which the input content starts to be played. When the time length from the time point at which the input content starts to be played to the current time point is shorter than the length of the measurement window, the audio signal processing device may acquire a loudness measurement value in the closest measurement period that comes after the current time point. In this case, the audio signal processing device may acquire a loudness measurement value corresponding to a section shorter than the length of the measurement window.

[0198] Specifically, the audio signal processing device can determine the measurement period based on the additional information. For example, the measurement period may be determined based on the length of the input content. For example, when the length of the second input content is longer than the length of the first input content, the measurement period of the first input content may be shorter than the measurement period of the second input content. Furthermore, the audio signal processing device can acquire loudness measurement values ​​for each measurement window based on the determined measurement period. In the embodiment of FIG. 18, the measurement period may be 100 ms. The audio signal processing device can move the measurement window every 100 ms and acquire loudness measurement values ​​for each measurement window. Furthermore, the audio signal processing device can acquire the above-mentioned loudness information based on the multiple loudness measurement values ​​measured in FIG. 18.

[0199] 19 is a flowchart showing an operation of an audio signal processing device according to an embodiment of the present invention. The audio signal processing device according to an embodiment of the present invention can receive an input audio signal (step S1901). At this time, the input audio signal can include the input content described in FIG. 2. Next, the audio signal processing device can receive loudness metadata corresponding to the input audio signal (step S1902).

[0200] Next, the audio signal processing device may parse the loudness metadata to acquire loudness information of the input audio signal (step S1903). According to an embodiment of the present invention, the loudness information may include at least one of information indicating a cumulative loudness level of the input audio signal, at least one short-term loudness level, a Quality Secure Histogram Index (QSHI), a dynamic range of the input audio signal, a frequency-specific loudness energy, a frequency-specific loudness ratio, and a peak envelope. The method of the audio signal processing device acquiring each piece of information included in the loudness information may be the embodiment described with reference to FIGS. 2 to 18.

[0201] The QSHI may indicate a threshold loudness level at which no cognitive sound quality impairment occurs. The QSHI may be acquired by the above-mentioned step S303 of FIG. 3, the QSHI extraction unit 404 of FIG. 4, and the embodiment described in FIG. 10. For example, the QSHI may be a loudness parameter calculated based on a loudness histogram of the input audio signal. In this case, the loudness histogram may be a size histogram of the time-specific short-section loudness level of the input audio signal. Alternatively, the loudness histogram may be a size histogram related to the peak value or root-mean-square (RMS) of each section of the input audio signal. The QSHI may be greater than the cumulative loudness level of the input audio signal.

[0202] According to an embodiment, the QSHI may be a parameter calculated based on a predicted loudness histogram predicted from a loudness histogram of an input audio signal, where the predicted loudness histogram may be a histogram generated based on a loudness parameter predicted when the input audio signal is output according to a target loudness level.

[0203] According to an embodiment, the QSHI may be determined based on the number of times a limiter is driven in the audio signal processing device. In this case, the audio signal processing device may apply a loudness limiter that limits the loudness level of an output audio signal to the output audio signal and output the output audio signal. In this case, the output audio signal may be a signal in which the output loudness level of an input audio signal is adjusted by a loudness gain. The QSHI may be a parameter set so that the short-term loudness level of the entire section of the output audio signal is equal to or lower than a previously set level.

[0204] Next, the audio signal processing device may obtain a loudness gain of the input audio signal based on the loudness information and the target loudness level (S1904). In one embodiment, the loudness gain of the input audio signal may be a fixed gain having a fixed value over the entire duration of the input audio signal. In another embodiment, the loudness gain of the input audio signal may be a gain that varies with time during the time the input audio signal is played back.

[0205] According to an embodiment of the present invention, an audio signal processing apparatus may receive a cumulative loudness of an input audio signal, and may determine a loudness gain based on the cumulative loudness of the input audio signal, a QSHI, and the target loudness level.

[0206] According to an embodiment, the audio signal processing device may compare a target loudness level of an input audio signal with the QSHI. The audio signal processing device may determine a loudness gain based on a comparison result. The audio signal processing device may determine a loudness gain based on a smaller value of the target loudness level of the input audio signal and the QSHI. In this regard, the specific embodiment described in FIG. 10 may be applied.

[0207] According to an embodiment, the audio signal processing device may obtain a loudness gain of an input audio signal based on a QSHI corrected from a QSHI of the input audio signal. For example, the audio signal processing device may perform post processing on the input audio signal. In this case, the audio signal processing device may receive post processing information indicating characteristics of the post processing on the input audio signal. Also, the audio signal processing device may correct the already acquired QSHI based on the post processing information. According to an embodiment, the audio signal processing device may correct the already acquired QSHI based on the post processing information and a function already stored. The audio signal processing device may correct the already acquired QSHI based on the post processing information and a look-up table already stored. In this case, the look-up table already stored may be a table including information regarding the QSHI correction according to the characteristics of the post processing. Also, the information regarding the QSHI correction may include information indicating a QSHI correction value according to the characteristics of the post processing. The audio signal processing device may obtain a QSHI correction value corresponding to the post processing on the input audio signal based on the look-up table already stored. The audio signal processing device can correct the acquired QSHI by adding a QSHI correction value to the QSHI. The audio signal processing device can determine a loudness gain of the input audio signal based on the QSHI corrected by the above-mentioned method.

[0208] According to an embodiment, the audio signal processing device may determine a loudness gain of the input audio signal based on frequency-specific loudness energy and post-processing information indicating characteristics of post-processing for the input audio signal. The audio signal processing device may determine a loudness gain of the input audio signal based on band-specific loudness levels that change due to post-processing.

[0209] According to an embodiment, the audio signal processing device may obtain a band-specific loudness level that changes due to post-processing based on frequency-specific loudness energy and post-processing information indicating a characteristic of post-processing for an input audio signal. The audio signal processing device may obtain a band-specific loudness level that changes due to post-processing based on frequency-specific loudness ratios and the post-processing information of the input audio signal. The band-specific loudness level that changes due to post-processing may be calculated based on an inner product of frequency-specific loudness ratios of the input audio signal. The band-specific loudness level that changes due to post-processing may also be a parameter obtained based on a cognitive loudness characteristic. The audio signal processing device may obtain a band-specific loudness level that changes due to post-processing of the input audio signal based on a loudness filter based on an auditory scale. Specifically, the loudness filter may be at least one of an inverse filter of equal-loudness contours or a K-weighting filter that approximates the inverse filter. When the loudness level of a particular frame among a plurality of frames included in the input audio signal is less than or equal to the relative threshold, the audio signal processing device may not calculate the band-specific loudness level that is changed by post-processing corresponding to the particular frame. As another example, the band-specific loudness level that is changed by post-processing of the input audio signal may be a parameter set based on at least one of the genre of the input audio signal and a user input.

[0210] The frequency-specific loudness ratio and / or frequency-specific loudness energy of the input audio signal may be values ​​calculated based on loudness measurement values ​​for the input audio signal. The frequency-specific loudness ratio may be a parameter obtained based on a cognitive loudness characteristic. The audio signal processing device may obtain the frequency-specific loudness ratio of the input audio signal based on a loudness filter based on a hearing scale. Specifically, the loudness filter may be at least one of an inverse filter of equal-loudness contours or a K-weighting filter that approximates the inverse filter. When a loudness level of a specific frame among a plurality of frames included in the input audio signal is less than or equal to a relative threshold, the audio signal processing device may not calculate a frequency-specific loudness ratio corresponding to the frame. The frequency-specific loudness ratio may be obtained by the embodiment described with reference to the frequency-specific loudness analysis unit 402 of FIG. 4. As another example, the frequency-specific loudness ratio of the input audio signal may be a parameter set based on at least one of a genre of the input audio signal and a user input.

[0211] The audio signal processing device may obtain post-processing information for an input audio signal based on a user input. In this case, the user input may be an input related to the input audio signal. Also, the user may be a user who uses the audio signal processing device. The post-processing information may include at least one of information indicating an output characteristic of the audio signal processing device, a genre of the input audio signal, a post-processing mode according to a user input, an equalization type, reverberation, and room compensation. The method of determining a loudness gain of an input audio signal based on a band-specific loudness level changed by post-processing by the audio signal processing device may be the embodiment described in step S303 of FIG. 3.

[0212] According to an embodiment, the audio signal processing device may determine a loudness gain of an input audio signal based on a loudness change prediction value. The loudness change prediction value may be a prediction value for a loudness change of the input audio signal due to post-processing. The audio signal processing device may acquire the loudness change prediction value based on post-processing information set by a user. The audio signal processing device may acquire the loudness change prediction value based on at least one of a frequency characteristic of the input audio signal and a band-specific loudness level changed by post-processing. The loudness change prediction value may be calculated based on an inner product of a frequency-specific loudness ratio of the input audio signal. The loudness change prediction value may be a parameter acquired based on a cognitive loudness characteristic. The audio signal processing device may acquire the loudness change prediction value of the input audio signal based on a loudness filter based on a hearing scale. Specifically, the loudness filter may be at least one of an inverse filter of equal-loudness contours or a K-weighting filter that approximates the inverse filter. When the loudness level of a specific frame among a plurality of frames included in the input audio signal is smaller than or equal to the relative threshold, the audio signal processing device may not calculate a loudness change prediction value corresponding to the frame. The method of the audio signal processing device to obtain the loudness change prediction value may be the embodiment described with reference to the frequency-specific loudness analysis unit 402 and the post-processing loudness prediction unit 403 in FIG. 4.

[0213] According to an embodiment of the present invention, an audio signal processing apparatus may determine a loudness gain of an input audio signal based on frame-by-frame loudness information of the input audio signal. The audio signal processing apparatus may obtain a frame-by-frame loudness gain of the input audio signal based on the frame-by-frame loudness information of the input audio signal. The loudness gain of the input audio signal may be a gain that changes with time during a time when the input audio signal is played back. According to an embodiment, the audio signal processing apparatus may receive loudness metadata including frame-by-frame loudness information of the input audio signal. The audio signal processing apparatus may parse the loudness metadata to obtain the frame-by-frame loudness information of the input audio signal. The frame-by-frame loudness information may include a dynamic loudness parameter. According to an embodiment, the frame-by-frame loudness information may include information indicating a frame-by-frame peak value. The frame-by-frame peak value may be obtained based on a maximum absolute value of an audio signal included in a frame of a previously set length.

[0214] According to an embodiment, the audio signal processing device may determine a loudness gain for each frame of an input audio signal based on a peak value for each frame of the input audio signal. The audio signal processing device may determine a loudness gain for each frame of an input audio signal based on a target loudness level and a peak value for each frame of the input audio signal. For example, the audio signal processing device may set a loudness gain for each frame based on the target loudness level so as not to exceed the peak value for each frame. Also, the audio signal processing device may adjust an output loudness level of a corresponding frame of the input audio signal based on the loudness gain for each frame. The embodiment described above with reference to FIG. 17 may be applied to a method in which the audio signal processing device determines a loudness gain based on the loudness information for each frame.

[0215] Next, the audio signal processing device may adjust an output loudness level of the input audio signal based on the loudness gain (S1905). According to an embodiment, the audio signal processing device may generate an output audio signal by adjusting the output loudness level of the input audio signal. In this case, the audio signal processing device may use the determined loudness gain. According to an embodiment, the audio signal processing device may apply a loudness limiter to the generated output audio signal and output it.

[0216] According to a further embodiment of the present invention, the audio signal processing device may adjust an output loudness level of an input audio signal based on a section loudness gain for a part of the entire section of the input audio signal. According to one embodiment, the audio signal processing device may obtain a loudness gain corresponding to a specific section of the input audio signal based on a loudness parameter corresponding to the specific section. For example, the loudness parameter corresponding to the specific section of the input audio signal may include at least one representative value for the specific section. In this case, the representative value may include at least one of a maximum absolute value of the loudness level of the input audio signal corresponding to the specific section and a short section loudness level.

[0217] According to an embodiment, the audio signal processing device may determine a loudness gain for each time section of the input audio signal based on a target loudness level, a cumulative loudness level, and an input loudness level. In this case, the input loudness level may be a loudness level representative of a specific section. For example, the input loudness level may be a short-section loudness level. The audio signal processing device may compare at least two of the target loudness level, the cumulative loudness level, the input loudness level, a relative threshold, a noise floor level, and a peak value with each other. Furthermore, the audio signal processing device may determine a loudness gain for each time section of the input audio signal based on a comparison result.

[0218] For example, the audio signal processing device may compare a target loudness level with a cumulative loudness level. The audio signal processing device may compare an input loudness level with a cumulative loudness level. If the target loudness level is smaller than the cumulative loudness level and the input loudness level is larger than the cumulative loudness level, the audio signal processing device may apply a first section-specific loudness gain to the input audio signal of the corresponding section.

[0219] As another example, when the target loudness level is greater than the cumulative loudness level, the input loudness level is less than the cumulative loudness level, and the input loudness level is greater than a relative threshold, the audio signal processing device can apply a second section-specific loudness gain to the input audio signal of the section.

[0220] As yet another example, when the target loudness level is greater than the cumulative loudness level, the input loudness level is less than the cumulative loudness level, the input loudness level is less than the relative threshold, and the input loudness level is greater than the noise floor level, the audio signal processing device can apply a third section-specific loudness gain to the input audio signal of the section.

[0221] In yet another embodiment, when the target loudness level is greater than the cumulative loudness level, the input loudness level is less than the cumulative loudness level, the input loudness level is less than the relative threshold, and the input loudness level is less than the noise floor level, the audio signal processing device may apply a fourth section-specific loudness gain to the input audio signal of the section. In this case, the fourth section-specific loudness gain may be the loudness gain of a frame prior to the frame. For example, when the target loudness level is greater than the cumulative loudness level, the input loudness level corresponding to the Nth frame is less than the cumulative loudness level, the input loudness level corresponding to the Nth frame is less than the relative threshold, and the input loudness level corresponding to the Nth frame is less than the noise floor level, the audio signal processing device may use the loudness gain corresponding to the N-1-th frame as the loudness gain corresponding to the Nth frame.

[0222] According to another embodiment, the fourth section loudness gain may represent a fixed gain applied to the entire input audio signal. Also, the first section loudness gain, the second section loudness gain, and the third section loudness gain may be gains corrected in individual ways based on the fourth section loudness gain. Also, the first section loudness gain, the second section loudness gain, and the third section loudness gain may be gains having individual values.

[0223] According to an embodiment, the loudness representative value of an Nth section of an input audio signal may be a representative value corresponding to a section adjacent to the Nth section of the input audio signal. For example, the loudness representative value of an Nth specific section of an input audio signal may be a representative value corresponding to an N+Lth or NLth section. In this case, L may be an index value corresponding to a section smaller than a time section for acquiring the representative value. For example, the time section for acquiring the representative value may be 3 seconds. In addition, the audio signal processing device may acquire a representative value of a specific section of an input audio signal based on a time-delayed input audio signal. In this case, the audio signal processing device may time-delay the input audio signal based on a previously set delay time and acquire at least one loudness measurement value used for acquiring the representative value.

[0224] According to an embodiment, the audio signal processing device may obtain a fixed loudness gain to be applied to the entire input audio signal. In this case, the audio signal processing device may correct the fixed loudness gain based on a loudness parameter corresponding to a specific section of the input audio signal. Furthermore, the audio signal processing device may adjust an output loudness level of the input audio signal for the section based on the corrected gain. The embodiment described above with reference to FIG. 17 may be applied to a method in which the input audio signal processing device adjusts the output loudness level of the input audio signal based on a section loudness gain for a part of the entire section of the input audio signal.

[0225] FIG. 20 is a block diagram showing a configuration of an audio signal processing device 2000 according to an embodiment of the present invention. According to an embodiment, the audio signal processing device 2000 may include a receiving unit 2100, a processor 2200, and an output unit 2300. However, all of the components shown in FIG. 10 are not necessarily essential components of the audio signal processing device. The audio signal processing device 2000 may further include components not shown in FIG. 20. For example, the audio signal processing device according to the embodiment may further include a storage unit (not shown). In addition, at least a part of the components of the audio signal processing device 2000 shown in FIG. 20 may be omitted. For example, the audio signal processing device according to the embodiment may not include at least one of the receiving unit 2100 and the output unit 2300.

[0226] The receiving unit 2100 may receive input content input to the audio signal processing device 2000. The receiving unit 2100 may receive input content whose output loudness level is adjusted by the processor 2200. As described above, the input content may include an audio signal. In this case, the audio signal may include at least one of an Ambisonic signal, an object signal, or a channel signal. In addition, the audio signal may be one object signal or a mono signal. The audio signal may be a multi-object or multi-channel signal. According to an embodiment, the receiving unit 2100 may include an input terminal for receiving input content transmitted via a wire. In addition, the receiving unit 2100 may include a wireless receiving module for receiving input content transmitted via a wireless connection.

[0227] According to an embodiment, the audio signal processing apparatus 2000 may include another decoder. In this case, the receiving unit 2100 may receive an encoded bitstream of the input content. The encoded bitstream may be decoded as the input content by the decoder. Furthermore, the receiving unit 2100 may receive additional information related to the input content.

[0228] According to an embodiment, the receiving unit 2100 may include a transmitting / receiving means for transmitting / receiving data to / from an external device via a network. In this case, the data may include at least one of a bit stream of input content or additional information. The receiving unit 2100 may include a wired transmitting / receiving terminal for receiving data transmitted via a wired connection. Also, the receiving unit 2100 may include a wireless transmitting / receiving module for receiving data transmitted wirelessly. In this case, the receiving unit 2100 may receive data transmitted wirelessly using a Bluetooth or Wi-Fi communication method. Also, the receiving unit 2100 may receive data transmitted according to a mobile communication standard such as LTE (long term evolution) or LTE-advanced, but the present disclosure is not limited thereto. The receiving unit 2100 may receive various types of data transmitted according to various wired and wireless communication standards.

[0229] The processor 2200 may control the overall operation of the audio signal processing device 2000. The processor 2200 may control each component of the audio signal processing device 2000. The processor 2200 may perform calculations and processes of various data and signals. The processor 2200 may be embodied by hardware in the form of a semiconductor chip or an electronic circuit, or by software that controls the hardware. The processor 2200 may be embodied in a form in which the hardware and the software are combined. For example, the processor 2200 may control the operations of the receiving unit 2100 and the output unit 2300 by executing at least one program. In addition, the processor 2200 may execute at least one program to perform the operations described in FIG. 1 to FIG. 19.

[0230] According to an embodiment, the processor 2200 may adjust an output loudness level of the input content. For example, the processor 2200 may adjust the output loudness level of the input content based on a loudness gain. The loudness information may be a loudness characteristic of the input content analyzed from the input content. In this case, the loudness gain may be obtained based on the loudness information. Also, the processor 2200 may output an output content with an adjusted output loudness level from the input content. In this case, the processor 2200 may output the output content from the output unit 2300 described later.

[0231] The output unit 2300 may output the output content. The output unit 2300 may output the output content in which the output loudness level is adjusted from the input content by the processor 2200. Here, the output content may include an output audio signal. In this case, the output audio signal may include at least one of an ambisonic signal, an object signal, or a channel signal. The output audio signal may be a multi-object or multi-channel signal. Also, the output audio signal may include a two-channel output audio signal corresponding to both ears of a listener. The output audio signal may include a binaural two-channel output audio signal. The output unit 2300 may output an audio headphone signal in which the output loudness level is adjusted by the processor 2200.

[0232] According to an embodiment, the output unit 2300 may include an output means for outputting output content. For example, the output unit 2300 may include an output terminal for outputting an output audio signal to the outside. In this case, the audio signal processing device 2000 may output the output audio signal to an external device connected to the output terminal. The output unit 2300 may include a wireless audio transmission module for outputting the output audio signal to the outside. In this case, the output unit 2300 may output the output audio signal to the external device using a wireless communication method such as Bluetooth or Wi-Fi.

[0233] Also, the output unit 2300 may include a speaker. In this case, the audio signal processing device 2000 may output an output audio signal from the speaker. Also, the output unit 2300 may further include a converter (e.g., digital-to-analog converter, DAC) for converting a digital audio signal into an analog audio signal. Furthermore, the output unit 2300 may include a display means for outputting a video signal included in the output content.

[0234] As described above, the audio signal processing apparatus 2000 may further include a storage unit (not shown). The storage unit may store at least one of data or programs for processing and control of the processor 2200. The storage unit may also store loudness information. The storage unit may store loudness information extracted from the received loudness metadata. The storage unit may store a received target loudness level. Or, the storage unit may store a loudness measurement value acquired by the processor 2200. The storage unit may also store a result calculated by the processor 2200. For example, the storage unit may store a loudness gain determined based on the loudness information. The storage unit may also store data input to the audio signal processing apparatus 2000 or output from the audio signal processing apparatus 2000.

[0235] The storage unit may include at least one memory, which may include at least one type of storage medium selected from the group consisting of flash memory type, hard disk type, multimedia card micro type, card type memory (e.g., SD or XD memory), random access memory (RAM), static random access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), programmable read-only memory (PROM), magnetic memory, magnetic disk, and optical disk.

[0236] FIG. 21 is a diagram illustrating peak values ​​for each time interval of an input audio signal according to an embodiment of the present invention. In the embodiment of FIG. 21, the peak values ​​for each time interval may be values ​​obtained based on loudness measurement values ​​measured from an input audio signal. In FIG. 21, values ​​indicated by a solid line indicate loudness measurement values ​​for each time interval of an input audio signal. Also, values ​​indicated by a first dashed line (-*-) indicate representative values ​​for each time interval of the time-based loudness measurement values ​​of an input audio signal. The audio signal processing device may obtain peak values ​​for each time interval based on the representative values ​​for each time interval. In this case, since the representative values ​​are calculated based on values ​​input to an input buffer of a loudness measuring device, errors may occur if the representative values ​​are calculated based on an actual input audio signal.

[0237] In FIG. 21, the value indicated by the second dashed line (-△-) may be a representative value for each time section obtained by a time delay of about 15 ms. The audio signal processing device may obtain a representative value for each time section by applying a time delay to the input audio signal. In this way, the audio signal processing device may correct the obtained peak value so that it can more accurately correspond to a loudness change of the input audio signal. In this case, a delay duration used for the time delay may be set based on the length of a measurement frame of the input audio signal. The time delay correction method of the peak value described in FIG. 21 may also be applied to other dynamic loudness parameters described in FIG. 15. For example, the audio signal processing device may obtain a short-term loudness level using a time delay.

[0238] 22 is a diagram illustrating a method for adjusting an output loudness level of an input audio signal using smoothing in an audio signal processing device according to an embodiment of the present invention. According to an embodiment of the present invention, the audio signal processing device can adjust the output loudness level of an input audio signal using smoothing so that the loudness gain changes gradually. In this case, since smoothing is performed based on the loudness measurement value of the input audio signal (causal processing), it may be difficult for the audio signal processing device to correctly provide parameters required in a corresponding frame for actual loudness changes.

[0239] Therefore, the audio signal processing device can perform a smoothing operation on the loudness gain of the input audio signal using the loudness parameter obtained by the time delay. In this case, the loudness parameter obtained by the time delay may be a parameter obtained by the method described above in FIG.

[0240] In FIG. 22, values ​​indicated by solid lines may represent loudness gains for each frame of an input audio signal. In this case, values ​​indicated by solid lines may represent loudness gains to which no smoothing has been applied. Also, values ​​indicated by the third dashed line (--) and the fourth dashed line (-·-) may represent loudness gains to which smoothing has been applied from the loudness gains for each frame. In this case, each of the frame loudness gains indicated by the third dashed line (--) may represent a first frame loudness gain (smoothing from shifted input) obtained based on a measurement value to which a time delay has been applied. Meanwhile, each of the frame loudness gains indicated by the fourth dashed line (-·-) may represent a second frame loudness gain (smoothing from org.input) obtained based on a measurement value to which no time delay has been applied.

[0241] Referring to FIG. 22, the second frame loudness gain may change more similarly to the loudness level of the input audio signal than the first frame loudness gain. Referring to the section of frame indexes 110 to 130 on the horizontal axis of FIG. 22, the frame loudness gain to which smoothing of the input audio signal is not applied suddenly decreases. In this section, the first frame loudness gain gradually decreases compared to the second frame loudness gain. The second frame loudness gain suddenly decreases compared to the first frame loudness gain. In addition, the first frame loudness gain starts to decrease a certain frame earlier than the second frame loudness gain. Thus, the audio signal processing device can prevent a listener from feeling a sudden loudness change by using the first frame loudness gain acquired based on a measurement value to which a time delay is applied.

[0242] According to an embodiment of the present invention, an audio signal processing device may apply a loudness gain determined for each section to an input audio signal in order to process the characteristics of the input audio signal according to a target loudness level. In this case, an excessive loudness gain value may be applied to a specific section. As a result, clipping greater than 0 dBFS may occur or a result greater than a predefined numerical value (threshold value) may occur. For this reason, the audio signal processing device may apply a limiter to an output audio signal. As a result, the audio signal processing device may apply a limiter to a section where the loudness level of an output audio signal, the output loudness level of which is adjusted from the input audio signal, is greater than a previously set loudness level.

[0243] In this case, the output audio signal may be processed by the limiter in real time or in a time sequence (causal processing) according to limiter parameters related to the limiter. When the audio signal processing device uses a limiter, the audio signal processing device may generate unintended timbre distortion. As described above, the audio signal processing device may adjust an output loudness level of an input audio signal by using a loudness gain determined for each section. At this time, the loudness gain determined for each section may be a gain considering a peak value for each section. The audio signal processing device may predict clipping occurring in a corresponding section or an occurrence of a section having a level exceeding a target loudness level based on the peak value for each section. Furthermore, the audio signal processing device may determine a loudness gain for each section of the input audio signal based on the prediction. That is, the audio signal processing device may conversely correct the loudness gain based on the prediction. As a result, the audio signal processing device may prevent timbre distortion of an output audio signal caused by the limiter.

[0244] Some embodiments may be embodied in the form of a recording medium including computer executable instructions such as program modules executed by the computer. The computer readable medium may be any available medium accessible by the computer, and may include both volatile and non-volatile media, and separate and non-separate media. The computer readable medium may also include computer storage media. The computer storage media may include both volatile and non-volatile, separate and non-separate media embodied in any method or technology for storage of information such as computer readable instructions, data structures, program modules, or other data.

[0245] Although the present disclosure has been described above using specific examples, those skilled in the art who have ordinary knowledge in the technical field to which the present disclosure belongs can modify and change the present disclosure without departing from the spirit and scope of the present disclosure. That is, although the present disclosure has described an example of loudness level adjustment for an audio signal, the present disclosure can be similarly applied and extended to various multimedia signals including video signals in addition to audio signals. Therefore, anything that can be easily inferred by a person skilled in the art in the technical field to which the present disclosure belongs from the detailed description and examples of the present disclosure is interpreted as falling within the scope of the present disclosure. [Explanation of symbols]

[0246] 801 Measurement Window 2000 Audio signal processing device 2100 Receiver 2200 Processor 2300 Output section

Claims

1. 1. An audio signal processing apparatus comprising: a receiving unit for receiving an input audio signal; a processor for generating loudness metadata corresponding to the input audio signal; and an output unit for transmitting loudness metadata generated by the processor; The processor, measuring the loudness of the input audio signal to obtain loudness information of the input audio signal; Transforming the loudness information to generate the loudness metadata; transmitting the generated loudness metadata from the output unit to an output device that outputs the input audio signal; The loudness information includes information indicating a quality secure histogram index (QSHI) of the input audio signal, the QSHI indicating a threshold loudness level at which no perceptual sound quality impairment occurs; Audio signal processing device.

2. The processor, obtaining the QSHI based on a loudness histogram of the input audio signal; The audio signal processing apparatus according to claim 1 .

3. The processor, obtaining the loudness histogram based on a distribution of at least one short-term loudness level of the input audio signal; Obtaining the QSHI based on the loudness histogram; The short-term loudness level is measured over a period shorter than the entire period of the input audio signal. The audio signal processing device according to claim 2 .

4. The loudness histogram is a size histogram relating to peak values ​​or root-mean-square (RMS) of each section of the input audio signal. The audio signal processing device according to claim 2 .

5. The processor, Predicting loudness parameters when the input audio signal is output according to a target loudness level based on a loudness histogram of the input audio signal; obtaining a predicted loudness histogram of the input audio signal based on the predicted loudness parameters; obtaining the QSHI based on the predicted loudness prediction histogram; The audio signal processing device according to claim 2 .

6. the loudness information comprises a cumulative loudness level of the input audio signal; The QSHI is greater than a cumulative loudness level of the input audio signal, the cumulative loudness level being a loudness level calculated based on loudness measurements acquired from a setup point in time set in an audio signal processing device. The audio signal processing apparatus according to claim 1 .

7. The QSHI is a parameter that is corrected depending on whether or not post-processing is performed on the input audio signal in the output device. The audio signal processing apparatus according to claim 1 .

8. The processor, setting a QSHI so that the short-term loudness level of the entire section of the input audio signal output from the output device is equal to or lower than a previously set level; The audio signal processing apparatus according to claim 1 .

9. 1. An audio signal processing apparatus comprising: a processor for adjusting an output loudness level of an input audio signal; The processor, receiving loudness metadata corresponding to the input audio signal; Parsing the loudness metadata to obtain loudness information for the input audio signal; determining a loudness gain for the input audio signal based on the loudness information and a target loudness level; adjusting an output loudness level of the input audio signal based on the loudness gain; The loudness information includes information indicating a quality secure histogram index (QSHI) of the input audio signal, the QSHI indicating a threshold loudness level at which no perceptual sound quality impairment occurs; Audio signal processing device.

10. The processor, comparing a target loudness level of the input audio signal with the QSHI and determining the loudness gain based on the comparison result; The audio signal processing apparatus according to claim 9 .

11. The processor, determining the loudness gain based on the smaller of a target loudness level of the input audio signal and the QSHI; The audio signal processing device according to claim 10.

12. The processor, receiving a cumulative loudness level of the input audio signal; determining the loudness gain based on a cumulative loudness level of the input audio signal, the QSHI and the target loudness level; The cumulative loudness level is a loudness level calculated based on loudness measurements obtained from a setup point in time set in a device for measuring the loudness of the input audio signal. The audio signal processing device according to claim 10.

13. The QSHI is a loudness parameter calculated based on a loudness histogram of the input audio signal. The audio signal processing device according to claim 10.

14. the loudness histogram is a size histogram of short-term loudness levels of the input audio signal over time, The short-term loudness level is measured over a period shorter than the entire period of the input audio signal. An audio signal processing apparatus according to claim 13.

15. The loudness histogram is a size histogram relating to peak values ​​or root-mean-square (RMS) of each section of the input audio signal. An audio signal processing apparatus according to claim 13.

16. The QSHI is a parameter calculated based on a predicted loudness histogram predicted from a loudness histogram of the input audio signal, and the predicted loudness histogram is a histogram generated based on loudness parameters predicted when the input audio signal is output according to the target loudness level. The audio signal processing device according to claim 10.

17. the QSHI is greater than a cumulative loudness level of the input audio signal, the cumulative loudness level being a loudness level calculated based on loudness measurements obtained from a setup point in a device that measures the loudness of the input audio signal; The audio signal processing device according to claim 10.

18. The processor, adjusting an output loudness level of the input audio signal by the loudness gain to generate an output audio signal; A loudness limiter that limits the loudness level of the output audio signal is applied to the output audio signal, and the output audio signal is output. The audio signal processing device according to claim 10.

19. The QSHI is a loudness parameter determined based on the number of times a limiter is activated in the audio signal processing device.

20. An audio signal processing apparatus according to claim 18.

20. The processor, performing post-processing on the input audio signal; receiving post-processing information indicating characteristics of post-processing for the input audio signal; correcting the obtained QSHI based on the post-processing information; determining the loudness gain based on the corrected QSHI; The audio signal processing device according to claim 10.

21. The processor, correcting the QSHI based on the post-processing information and a previously stored function; 21. An audio signal processing apparatus according to claim 20.

22. The processor, correcting the QSHI based on the post-processing information and a previously stored look-up table; The previously stored lookup table includes information regarding QSHI correction according to post-processing characteristics; 21. An audio signal processing apparatus according to claim 20.

23. The information regarding the QSHI correction includes information indicating a QSHI correction value according to a characteristic of post-processing, The processor, Obtaining a QSHI correction value corresponding to post-processing of the input audio signal based on the previously stored look-up table; adding the QSHI correction value to the acquired QSHI to correct the QSHI; 23. An audio signal processing apparatus according to claim 22.

24. The loudness gain is a fixed gain having a fixed value throughout the entire duration of the input audio signal. The audio signal processing device according to claim 10.

25. the loudness gain is a time-varying gain over the time that the input audio signal is played; The audio signal processing device according to claim 10.

26. The processor, adjusting an output loudness level of the input audio signal by the loudness gain to generate an output audio signal; The QSHI is a parameter set so that the short-term loudness level of the entire section of the output audio signal is equal to or lower than a previously set level. The audio signal processing device according to claim 10.

Images