Dynamic range compression with reduced artifact

Abstract

To provide a method and a system for performing dynamic range compression (DRC) on audio in a manner intended to reduce or prevent undesirable artifacts in the output audio, such as pumping and breathing.SOLUTION: A DRC system performs DRC to maximize the average loudness and reduce or prevent distortion during playback. When the average loudness of the input audio approaches, meets, or exceeds a target, knee point for DRC or a signal level near the maximum playback level of the intended playback system, then it is assumed that such input audio is already compressed and therefore applies reduced DRC or full DRC to the input audio.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to European Patent Application No. 19197154.8, filed September 13, 2019, and U.S. Provisional Patent Application No. 62 / 899,769, filed September 13, 2019, which are incorporated herein by reference.

[0002] Technical Field The present disclosure relates to dynamic range compression of audio signals. [Background technology]

[0003] Herein, dynamic range compression is sometimes referred to as "DRC" and dynamic range compressor is sometimes referred to as "DRC".

[0004] 1, a traditional dynamic range compressor ("DRC") includes a level estimator 1, a dynamic range compression (DRC) gain determination subsystem 6, and a gain application subsystem 7 coupled as shown. In some embodiments, the gain determination subsystem 6 includes a smoother 3 and a dynamic range compression (DRC) gain curve subsystem 5 coupled as shown. Subsystem 7 is coupled and configured to apply a time-varying gain g(t) (e.g., a series of gain values) output from subsystem 6 (e.g., from subsystem 5 of subsystem 6 as shown in FIG. 1) to an input audio signal to generate an audio output signal.

[0005] The dynamic range compression applied to the input audio signal may reduce the power of segments of the input audio signal whose smoothed level (output from smoother 3) is above a threshold (a first knee point) (i.e., subsystem 7 may apply segment gain(s) determined by subsystem 6 below gain(s) 1) and increase the power of segments of the input audio signal whose smoothed level (output from smoother 3) is below a second threshold (a "lower" knee point) (i.e., subsystem 7 may apply a gain greater than 1 determined by subsystem 6 to such segments).

[0006] Dynamic range compression (DRC) has an attack (an attack section that begins at or near each time the input audio level (as indicated, for example, by the output of Level Estimator 1) rises to the knee point and has a duration known as the attack time) and a release (a release section that begins at or near each time the input audio level falls to the knee point and has a duration known as the release time). The full DRC is applied during the section after the attack and before the release. The amount of DRC applied can increase from zero (when Subsystem 6 outputs Gain 1) to the full amount during the attack, then back to zero during the release.

[0007] One important possibility in DRC is that there is a large gain for low level input audio below the knee point, and then the gain decreases monotonically to a gain of 1 as the input signal level approaches its maximum level. Thus, DRC never actually reduces the higher levels of the input audio, but instead only increases the lower levels of the input audio. Such cases arise when DRC is used in an attempt to get maximum loudness from a low power system.

[0008] When the input audio signal jumps to a maximum or minimum level, this change is indicated by the output of the level estimator 1 in FIG. 1, but the DRC gain (output from the subsystem 6) typically does not immediately change to its full value (i.e., the value it would have if the input audio signal level was fixed at the maximum or minimum level and did not jump to the maximum or minimum level). Instead, the DRC gain changes smoothly to its full value (e.g., due to the presence of the smoother 3 in FIG. 1). The time required for the DRC gain to reach its full value (after the input signal level jumps to the maximum level) is the attack time, and the time required for the DRC gain to reach its full value (after the input signal level jumps to the minimum level) is the release time. Since the DRC gain typically approaches its full value exponentially, when attack and release times are quoted (e.g., in a system specification), the quoted attack (or release) time is often the time required for the DRC gain to reach halfway towards its full value.

[0009] In the implementation shown in FIG. 1, smoother 3 (i.e., the smoothing time constant used by smoother 3) determines the attack and release times (the attack time may be equal to or different from the release time, or one or both may be zero).

[0010] In other implementations of subsystem 6 (not specifically shown in FIG. 1 ), smoother 3 is replaced by another element (e.g., a smoother that operates on the gain values ​​output from DRC gain curve subsystem 5) or a subsystem that determines the attack and release times for each interval for which DRC is applied by subsystem 6. Generally, subsystem 6 is configured to determine (e.g., in response to user selection) the attack and release times for each interval for which subsystem 6 applies DRC (i.e., each interval for which subsystem 6 outputs a gain other than unity).

[0011] In some implementations of dynamic range compression, the compression performance is split, with a gain application subsystem (e.g., subsystem 7) implemented in the decoder or playback system or device, and other elements of the compression (e.g., subsystems 1 and 6) implemented in the encoder, such that the gain g(t) is sent (to the decoder or playback system or device) as metadata along with the input audio in the encoded bitstream. Some embodiments of the present invention (described below) contemplate such implementations.

[0012] The level estimator 1 is coupled and configured to determine and provide a level estimate to a subsystem 6 (e.g., to the smoother 3 in the implementation shown in FIG. 1). The level estimate is an estimate (typically varying over time) of the loudness of the input audio signal (e.g., the level estimate represents a sequence of average level or average power values, each averaging time being long enough for stability of the dynamic range compression applied by the system of FIG. 1). One typical level estimate is average power. Another example of a level estimate is loudness defined by the ITU-R BS.1770 loudness standard. The smoother 3 is coupled and configured to apply smoothing to the level estimate output from the estimator 1 and generate (and assert to the subsystem 5) a smoothed estimate of the average level or power of the input audio signal (the smoothed level estimate).

[0013] In the implementation shown in FIG. 1, in response to the smoothed level estimates (e.g., a smoothed sequence of average level or power values) determined by the smoother 3, the subsystem 5 determines a sequence of values ​​of the gain g(t). The subsystem 5 implements a function (typically called a "DRC gain curve") that maps each value (of the average level or power) output from the smoother 3 to a value (gain value) of the gain g(t). The gain element 7 applies the gain g(t) to the input audio signal to generate an output audio signal (which is a dynamic range compressed version of the input audio signal), e.g., by applying each value of the (sequence of values ​​of) the gain g to a corresponding value of the input audio signal (e.g., a sequence of its values).

[0014] In some other implementations, subsystem 6 applies a DRC gain curve that maps each value (of average level or power) output from level estimator 1 (rather than from smoother 3 as shown in FIG. 1 ) to a value of gain g(t) (gain value) (including by implementing DRC attack and release (with determined attack and release times for each interval of DRC application by subsystem 6)), and the gain value g(t) (optionally modified to implement the attack or release) is provided to gain element 7. Summary of the Invention [Means for solving the problem]

[0015] Some embodiments of the present invention are methods for generating output audio for (e.g., optimized for) playback by a system or device (e.g., a notebook, laptop, tablet, sound bar, mobile phone, or other device including or for use with small speakers) having limited power processing capabilities, and preferably performing dynamic range compression (DRC) on an audio signal in a manner intended to also reduce or prevent the occurrence of undesirable artifacts in the output audio (e.g., known as "pumping" and "breathing"). In some embodiments, the DRC is performed (or in a manner intended to) maximize average loudness (or provide a sufficiently large average loudness) during playback (or while preventing loss of quieter elements of the audio) and also reduce or prevent distortion (e.g., to reduce or prevent the occurrence of pumping and / or breathing artifacts and / or to reduce or prevent timbre changes due to frequency components produced by the non-linear gain application of the DRC). Some embodiments perform DRC on an audio signal in a manner intended to optimize content for radio broadcast, or the general audibility of audio content or components within an audio stream.

[0016] The expression "DRC application time" may be used herein to refer to the attack time (or release time) of an instance of application of DRC (e.g., an instance of application that applies a gain that is not unity, or an instance of application in which the DRC gain curve determines a gain that is not unity after the attack and before the release), or the duration of such an instance of application of DRC (including the attack and release).

[0017] In a first class of embodiments of the dynamic range compression (DRC) method of the present invention, a reduced DRC gain (e.g., no DRC) is applied to the input audio signal when the average loudness (e.g., average level or power) of the input audio signal approaches (or meets or exceeds) a target, since such input audio signal is assumed to already be compressed (e.g., maximizing loudness while preventing quieter elements of the audio from being lost during playback). Otherwise, a full DRC is applied to the input audio signal. The application of a reduced DRC (e.g., no DRC) when a full DRC is unnecessary reduces or prevents the occurrence of pumping and / or breathing artifacts that would result from a full DRC. The average loudness is determined over a time ("averaging" time) that is longer (e.g., much longer) than the DRC application time of the DRC. The target may be a target signal level or a target signal power. In typical embodiments of the first class, the target is an audio signal level that is close to (e.g., equal to or substantially equal to) the knee point for the DRC, or a maximum playback level of the playback system or device that reproduces the output audio.

[0018] A second class of embodiments of the dynamic range compression (DRC) method of the present invention is directed to reducing pumping artifacts during the execution of DRC for input audio having regular transients (e.g., sequences of identical or similar transients). Exemplary embodiments of the second class control the release time constant (of the release of each application of dynamic range compression). This includes by implementing a first release time constant (referred to as a relatively slow release time constant) when a segment of the input audio signal includes regular transients (including by applying a smoothed dynamic range compression gain to the segment of the input audio signal) and by implementing a relatively fast release time constant (i.e., a release time constant faster than the first release time constant) when a different segment of the input audio signal does not include regular transients (including by applying a non-smoothed dynamic range compression gain to the different segment of the input audio signal). When the relatively slow release time constant is implemented, pumping artifacts are reduced or prevented from occurring.

[0019] A third class of dynamic range compression (DRC) method embodiments of the present invention are directed to reducing breathing artifacts during the performance of DRC on decaying input audio. Exemplary embodiments of the third class control a release time constant (of the release of each application of dynamic range compression) in response to a loudness gradient of the input audio signal. This control typically implements a faster release time constant in response to increased steepness of the loudness gradient (to reduce or prevent the occurrence of breathing artifacts) and a slower release time constant in response to decreased steepness of the loudness gradient (to reduce or prevent the occurrence of pumping artifacts).

[0020] Another aspect of the invention is a system (e.g., a dynamic range compressor) or device configured to perform any embodiment of the method of the invention on an input audio signal. In one class of embodiments, the invention is a system (e.g., a dynamic range compressor) or device configured to perform dynamic range compression (according to any embodiment of the method of the invention) to generate dynamic range compressed audio, and to perform playback of the dynamic range compressed audio (e.g., a notebook, laptop, tablet, sound bar, mobile phone, or other device having (or for use with) small speakers, or a playback system having limited (e.g., physically limited) power processing capabilities).

[0021] In some embodiments, a system of the present invention is or includes a general-purpose or special-purpose processor that is programmed with software (or firmware) and / or otherwise configured to perform an embodiment of the method of the present invention. In some embodiments, a system of the present invention is a general-purpose processor that is coupled to receive input audio data and programmed (with appropriate software) to perform an embodiment of the method of the present invention thereby generating output audio data. In some embodiments, a system of the present invention is a digital signal processor that is coupled to receive input audio data and configured (e.g., programmed) to perform an embodiment of the method of the present invention thereby generating output audio data in response to the input audio data.

[0022] Aspects of the present invention include a system configured (e.g., programmed) to perform any of the embodiments of the methods of the present invention, and a computer readable medium (e.g., disk) storing code for carrying out any of the embodiments of the methods of the present invention. [Brief description of the drawings]

[0023] [Figure 1]1 is a block diagram of a conventional system configured to perform dynamic range compression on an input audio signal.

[0024] [Diagram 2] FIG. 1 is a block diagram of one embodiment of the dynamic range compression system of the present invention.

[0025] [Figure 2A] FIG. 2 is a block diagram of another embodiment of the dynamic range compression system of the present invention.

[0026] [Diagram 3] FIG. 2 is a block diagram of another embodiment of the dynamic range compression system of the present invention.

[0027] [Figure 4] FIG. 2 is a block diagram of another embodiment of the dynamic range compression system of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Some embodiments of the present invention provide improvements and technical solutions for reducing or preventing the occurrence of undesirable (e.g., annoying) artifacts known as "pumping" and "breathing" as a result of dynamic range compression. Different classes of embodiments implement different approaches (described herein) for preventing or reducing such pumping and breathing artifacts.

[0029] A first class of embodiments of the dynamic range compressor and dynamic range compression (DRC) method of the present invention will be described with reference to Fig. 2. In some embodiments of this class, the DRC applies (or the dynamic range compressor is configured to apply) a reduced DRC (or no DRC) to the input audio signal when the average level (or power) of the input audio signal approaches (or matches or exceeds) a target (e.g., a high average level), since such an input audio signal is assumed to be already compressed. The average level (or power) of the input audio signal is determined over a time ("averaging time") that is longer (e.g., much longer) than each attack time and / or each release time of the dynamic range compression, and the reduced DRC is applied "when" the signal has the average level (or power). This is in the sense that it is applied to each segment (of duration equal to or greater than the averaging time) of the input audio signal that has the average level (or power). With reference to the first class of embodiments, the term "target" is used broadly to denote a target signal level (or signal power) such that it can be reasonably assumed that the input audio signal has already been compressed such that its average level (or power) approaches (or meets or exceeds) the target. In typical embodiments of the first class, the target level is an audio signal level that is close to the knee point for DRC or the maximum playback level of the playback system or device that reproduces the output audio.

[0030] The dynamic range compressor of Figure 2 is an exemplary embodiment of a first class of embodiments. The compressor of Figure 2 differs from the conventional dynamic range compressor of Figure 1 in that the compressor of Figure 2 includes a slow smoother 2 and a gain adjustment subsystem 4 coupled as shown (as opposed to the compressor of Figure 1). The other elements of the DRC of Figure 2 (elements 1, 6, and 7) are identical to the corresponding (same-numbered) elements of the DRC of Figure 1. Subsystem 6 of Figure 2 may be implemented in any of the ways that subsystem 6 of Figure 1 may be implemented (e.g., including elements 3 and 5 of Figure 1).

[0031] A typical DRC gain curve (e.g., implemented by subsystem 5 of FIG. 1 or FIG. 2) determines gain values ​​(values ​​of gain g(t) of FIG. 1 or FIG. 2) such that: 1 in response to the audio signal having a high average level or power (e.g., the smoothed level output from the smoother 3) being above a threshold (knee point). 1, and in response to the audio signal having an average level or power (e.g., a smoothed level output from the smoother 3) below the knee point but above a second threshold (second knee point). a threshold value greater than 1 in response to the audio signal having a low average level or power below the second threshold; Thereby, the DRC (which generates the output audio signal in response to the input audio signal) maintains a monotonically increasing average output audio signal level (or power) as the average input signal level (or power) increases. The gain value determined by the DRC gain curve (and output from subsystem 6 in FIG. 1 or FIG. 2) changes dynamically as the average level (or power) of the input audio signal changes. However, this can result in undesirable artifacts (e.g., pumping artifacts) in the output audio signal, especially when the average level (or power) of the input signal is near the knee point of the DRC gain curve.

[0032] The inventors have come to realize that if an input audio signal is already sufficiently compressed (and can be reproduced with sufficient loudness by the intended reproduction device), then an ideal DRC system would apply less DRC (e.g., no DRC) to such input audio signals than it applies to other input audio signals. In other words, an ideal DRC system would be "unobtrusive" (and thus not introduce significant pumping artifacts) to sufficiently compressed (and sufficiently loud) input audio signals. The inventors have further come to realise that if an input audio signal has an average level or power that approaches (or matches or exceeds) an appropriate target value (e.g., a target value that is high enough that it can be reasonably assumed that the input audio signal has already been compressed and can be reproduced with sufficient loudness by the intended reproduction device), and if the average is determined over a sufficiently long time interval (i.e., a period that is longer (e.g., much longer) than each attack and / or release time of the dynamic range compression), then the DRC system should apply less DRC to such input audio signal than it applies to other input audio signals (i.e., the DRC system should "stay out of the way" and therefore not introduce significant pumping artifacts into the input audio signal).

[0033] 2, slow smoother 2 generates (and provides to gain adjustment subsystem 4) a slowly smoothed version of the level (or power) estimate output by level estimator 1. The output of slow smoother 2 is an estimate of the average level or power of the input audio signal, the average over a longer (e.g., much longer) time than the attack (and / or release) time employed by subsystem 6 (or than the duration of each application, including attack and release, of a non-unity gain DRC by subsystems 6 and 7).

[0034] The expression "DRC application time" may be used herein to refer to the attack time (or release time) of an instance of application of DRC (e.g., an instance of application that applies a gain that is not unity, or an instance of application in which the DRC gain curve determines a gain that is not unity after the attack and before the release), or the duration of such an instance of application of DRC (including the attack and release).

[0035] The term "loudness" is used herein to denote level (eg, average level) or power (eg, average power).

[0036] Thus, slow smoother 2 is configured to determine an average loudness of the input audio signal, where the average is over a time period longer (e.g., much longer) than a DRC application time (e.g., a typical DRC application time) implemented by subsystems 6 and 7. In some embodiments (e.g., the embodiment described below with reference to FIG. 2A), the loudness is determined from metadata provided along with (e.g., included in) the input audio signal. The output of slow smoother 2 is used by gain adjustment subsystem 4 to limit the gain output by DRC subsystem 6 (i.e., the gain indicated by the time-varying gain g(t) output from DRC subsystem 6). Subsystem 4 is coupled and configured to operate in response to a target (target level or power) identified in FIG. 2 as "Target." When the output of slow smoother 2 (average of the input audio signal level or power) approaches (or meets or exceeds) the target, subsystem 4 asserts control data (identified in FIG. 2 as a "gain adjustment" value) to subsystem 6 to cause the gain output by subsystem 6 to approach a gain of 1 (i.e., equal to a gain of 1 or closer to a gain of 1 than if subsystem 4 were disabled or omitted). In some implementations, the difference between the current output of slow smoother 2 and the target determines the current output of each of the gain adjustment values.

[0037] Thus, the DRC system of FIG. 2 "gets out of the way" (i.e., applies a reduced DRC, e.g., no DRC) if the output of slow smoother 2 approaches (or meets or exceeds) the target, and applies full DRC (i.e., the DRC that would be applied if subsystems 2 and 4 were omitted or disabled) otherwise.

[0038] The target (in response to which subsystem 4 operates) may be the knee point of the DRC applied by subsystem 6 (e.g., when the output of slow smoother 2 is at least substantially equal to the knee point, subsystem 6 outputs a gain of 1). The knee point may be an input signal level above which the DRC gain curve specifies a gain value less than 1, and thus, when the output of slow smoother 2 is at least substantially equal to such a knee point, it is reasonable to assume that the input audio is already compressed. In some other embodiments, the target is a value equal (or substantially equal) to the maximum playback level of the playback system or device that reproduces the output audio. At such a target, it is also reasonable to assume that the input audio is already compressed.

[0039] One traditional approach to DRC (e.g., the DRC performed by the system of FIG. 1) is to apply some slow-moving AGC (automatic gain control) before the DRC, match the average level of the AGC-leveled audio content to a desired target level (before applying the DRC), and implement the DRC gain curve to have a guard band around this target level (so that for each segment of AGC-leveled audio that has an average level within the guard band, the DRC is not applied, e.g., the DRC applies a gain of 1). However, when traditional DRC (with or without guard bands) is performed on the AGC-leveled audio, undesirable DRC artifacts (e.g., pumping and / or breathing) can result. Also, traditional guard bands may be placed in a non-optimal manner to reduce pumping or other artifacts. In addition, playback systems (implementing traditional DRC) often do not know the average mastering level of the original content (before the application of AGC), so the system's behavior cannot reasonably assume that reduced DRC (or no DRC) should be applied to any segment of AGC-leveled audio. Depending on the characteristics of the original (pre-AGC) content, it may not be desirable to run DRC on the AGC-leveled audio, even if there is a guard band around the AGC target level. Also, unknown digital volume control is often applied to the input audio, and traditional AGC levelers will "fight" against such volume control, resulting in an unappealing user experience during playback.

[0040] In contrast to traditional approaches, the system of FIG. 2 performs DRC in a manner controlled (in part) by the average level or power of the input audio (i.e., the output of slow smoother 2 of FIG. 2), where the average is determined over an interval that is longer (e.g., much longer) than each attack and / or each release time of the application (at non-unity gains) of DRC by subsystems 6 and 7 (or longer (e.g., much longer) than the duration of each application, including attack and release, by subsystems 6 and 7 of DRC at non-unity gains). When AGC is performed on the input audio signal of FIG. 2, the signal level (or power) whose average is determined (by subsystem 4 of FIG. 2) so that the resulting average level or power controls the DRC should be the level or power of the original signal before application of the AGC.

[0041] To understand the benefits of a typical operation of the system of FIG. 2 (and other embodiments of the first class), consider the case where the input audio signal is a well-mastered signal that is on average exactly at the right level, and thus the input audio signal (the signal that undergoes DRC) has already been through various compressions. This is likely to be the case for music, since engineers know that mastered music is likely to be played in environments with a lot of background noise (such as in a car). The best that the DRC embodiment of the present invention can do in this case is to leave the input signal completely intact. Even well-compressed tracks contain soft (quiet) bits. For example, a drum hit is generally followed by a reverberant tail that should include nearly all input levels and gradually fade away. Typically, any traditional DRC method results in boosting the quiet bits, because that is essentially what dynamic range compression means. But the resulting output audio does not sound as good as doing nothing. Running a traditional DRC on a well-mastered track that is already compressed would be a departure from the artist's intent.

[0042] In contrast, the DRC control applied by the system of FIG. 2 (i.e., the control performed by elements 2 and 4 of FIG. 2) is determined by a slowly smoothed (averaged) version of the input signal level (or power), so that when the averaged input level or power (as indicated by the output of slow smoother 2) is close to (or matches or exceeds) the target (as would be the case for well-mastered, sufficiently loud, input audio), the DRC is effectively disabled or reduced.

[0043] As a practical matter, when audio is played back by a laptop or cell phone (or other playback system or device with limited power processing capabilities), the user typically struggles to get a playback level high enough for comfortable listening. To achieve reasonable loudness playback using a playback device, the target digital averaged playback level typically must be very high. The exact value of the target averaged level is highly dependent on the particular device, but is typically high (i.e., substantially equal to or greater than the typical value of the target provided to subsystem 4 of the embodiment of FIG. 2). For music (or other audio) to achieve such a high input average level, it would have to have already undergone significant compression. It thus turns out that the best thing for a DRC system to do is to leave it alone. The operation of a typical implementation of the system of FIG. 2 disables or reduces the application of DRC to such music (or other audio).

[0044] Input audio (e.g., a music track) that has an average input level (as determined by the output of an exemplary implementation of Slow Smoothener 2 of FIG. 2) significantly lower than the target (provided to Subsystem 4 of the embodiment of FIG. 2) will have peaks that are much louder than the average level and quieter bits that are lower than the average level. In this case, it should be assumed that the lower digital levels are intended to be audible and further dynamic range compression is required. The operation of the exemplary implementation of the system of FIG. 2 does not disable or reduce the application of DRC to such input audio.

[0045] It should be understood that the slow moving average of the level or power of the audio signal (indicated by the output of slow smoother 2 in FIG. 2) already imposes a constraint on the dynamic range of the signal. If the slow moving average is close to the DRC knee point, or close to the maximum signal level, the DRC curve (implemented by DRC subsystem 6 in FIG. 2) does not need to be applied anymore (or even applied at all) ("maximum signal level" here denotes the maximum playback level of the intended playback system or device).

[0046] Next, referring to Fig. 2A, another embodiment in the first class of embodiments above will be described. The system of Fig. 2A (dynamic range compressor or DRC) differs from the system of Fig. 2 (also dynamic range compressor or DRC) in that the DRC of Fig. 2A includes an average loudness determination subsystem 8 rather than a slow smoother 2. The other elements of Fig. 2A (elements 1, 4, 6, and 7) are identical to the corresponding (same-numbered) elements of Fig. 2. Subsystem 6 of Fig. 2A may be implemented in any of the ways that subsystem 6 of Fig. 2 may be implemented (e.g., including elements 3 and 5 of Fig. 1).

[0047] DRC according to some embodiments of the present invention (e.g., the exemplary embodiment of FIG. 2A ) is implemented in a digital signal processor (e.g., programmed in software) configured to apply loudness-based processing to input audio data representing an audio program (e.g., implementing a “Dolby Volume” playback volume control or another type of playback loudness control or loudness leveling). Such loudness-based processing may use metadata (provided with and corresponding to the audio data) that indicates the loudness of the audio content and / or the loudness processing state of the audio content (e.g., what type of loudness processing has been performed on the audio content).

[0048] In the system of FIG. 2A , average loudness determination subsystem 8 is configured to determine (and provide to gain adjustment subsystem 4) data indicative of an average loudness (e.g., average level) of the input audio data (input audio signal), where the average is over a longer (e.g., much longer) time (an “averaging” time) than each attack and / or release time of dynamic range compression applied by subsystems 6 and 7 (or moreover than the duration of each application, including attack and release, of DRC by subsystems 6 and 7 at a non-unity gain). In some implementations, the input audio data is included in a “Dolby Digital” bitstream (which also includes metadata corresponding to the audio data). In some implementations, subsystem 8 may be configured to parse the metadata to identify metadata indicative of the loudness of each segment (e.g., frame) of a sequence of segments of the input audio data, and, if necessary, determine from the metadata a sequence of averages of such loudness (where each average in the sequence is over a sufficiently long averaging time). In some implementations, subsystem 8 may implement models of the behavior of the middle ear and the cochlea, as well as a psychoacoustic model of loudness.

[0049] The output of subsystem 8 is used (in subsystem 4 of FIG. 2A) in the same way that the output of slow smoother 2 is used (in subsystem 4) in the embodiment of FIG.

[0050] 2A system (or subsystem 6 of another embodiment of the invention) implements a DRC curve that maps input loudness to output loudness (thus subsystem 6 outputs loudness difference values ​​rather than gain values). In such implementations, subsystem 7 maps each loudness difference value to a corresponding gain change to be applied to the input audio signal.

[0051] For many applications, it may be desirable to employ a multiband implementation of the system (dynamic range compressor) of FIG. 2 or FIG. 2A (or a multiband implementation of the system of FIG. 3 or FIG. 4, described below).

[0052] In a multiband implementation of the system of FIG. 2 (or FIG. 2A), the input audio is divided (e.g., by a filter bank) into multiple frequency bands. For each of the frequency bands, an average loudness (e.g., average loudness, or average level, or average power, as indicated by metadata or averaged metadata) is determined (by subsystem 2 of FIG. 2 or subsystem 8 of FIG. 2A). For each band, the average loudness is over a longer (e.g., much longer) time (the "averaging" time) than each attack and / or release time of the dynamic range compression applied by subsystems 6 and 7 (or the duration of each application, including attack and release, of DRC by subsystems 6 and 7 at a non-unity gain). Subsystem 6 implements a set of DRC gain curves (one DRC gain curve for each frequency band). For each frequency band, a sequence of gain values ​​(output from subsystem 6 for that band) is applied (by subsystem 7) to the corresponding band of the input audio, thereby generating each frequency band of the output audio. The frequency bands of the output audio may be combined to generate an output audio signal. In other words, a DRC gain value (for each band) determined by the DRC gain curve may be applied at each band of the input audio to generate "dynamic range compressed" audio at each band, and then the "dynamic range compressed" audio (at each of the individual bands) may be combined to form the output audio signal. In one embodiment, a DRC gain may thus be determined for at least one frequency band of the plurality of frequency bands, and the DRC gain may be applied to the frequency band.

[0053] In some implementations, subsystem 4 uses the average loudness values ​​determined for each of the individual frequency bands (in such implementations, each of the gain adjustment values ​​is for an individual frequency band of the input audio) to determine the "gain adjustment" value (shown in Figs. 2 and 2A) used to control the application of the DRC. In some other implementations, a single (wideband) average loudness value is determined (by subsystem 2 of Fig. 2 or subsystem 8 of Fig. 2A), and this single average loudness value (which typically varies over time since it is for a sequence of different segments of the input audio) is used by subsystem 4 to determine the "gain adjustment" value (shown in Figs. 2 and 2A) used to control the application of the DRC. In the latter implementations, each of the gain adjustment values ​​(for the wideband input audio, not for the individual frequency bands of the input audio) is applied to all of the DRC gain curves (and each DRC gain curve is for a different one of the frequency bands). In some of the latter implementations, the difference between the wideband average loudness value and the target is used to generate the gain adjustment value used to control the application of the DRC gain curves per band.

[0054] In a multiband implementation, the DRC gain determination (applied by subsystem 7) typically involves smoothing the gains (e.g., the gains determined by the DRC gain curves for each of the bands) across the bands to improve timbre. In a multiband implementation, different bands may have different DRC knee points, and thus the targets (typically selected broadband targets) do not necessarily coincide with specific knee points for each of the bands.

[0055] The inventors contemplate that various known methods that may reduce pumping and breathing artifacts in a DRC (e.g., some methods of the type implemented in the "Dolby Volume" loudness level leveler) may be implemented in combination with some embodiments of the DRC of the present invention. Examples of such methods include: Auditory scene analysis. Gain changes are applied with greater strength in response to auditory scene changes; Hierarchical constraints: The gains in the individual frequency bands are constrained by the channel gains, which are in turn constrained by the sum level. For example, a DRC system implemented according to FIG. 2A (or FIG. 2) above may also implement audio scene analysis to further control the execution of the DRC.

[0056] A second class of embodiments of the present invention is directed to reducing pumping artifacts during the performance of DRC for input audio having regular transient components (e.g., sequences of identical or similar transient components). Exemplary embodiments in the second class control (e.g., include a subsystem configured to control) a release time constant (of the release of each application of dynamic range compression) by implementing a first release time constant (referred to as a relatively slow release time constant) when a segment of the input audio signal includes regular transient components (including by applying a smoothed dynamic range compression gain to the segment of the input audio signal) and implementing a relatively fast release time constant (i.e., a release time constant faster than the first release time constant) when a different segment of the input audio signal does not include regular transient components (including by applying a non-smoothed dynamic range compression gain to the different segment of the input audio signal). When the relatively slow release time constant is implemented, pumping artifacts are reduced or prevented from occurring.

[0057] In audio (especially music), there are often regular transients that cause a repeated attack and release of a typical DRC (Dynamic Range Compressor). This can result in a well-known and annoying artifact (produced by dynamic range compression) known as pumping. An aspect of the present invention aims to solve this problem and provide a technical advantage by modifying the release behavior of a dynamic range compressor.

[0058] An exemplary embodiment of the second class is described with reference to Figure 3. The dynamic range compressor of Figure 3 differs from the conventional dynamic range compressor of Figure 1 in that the compressor of Figure 3 includes a smoother 11 and a gain adjustment subsystem 13 combined as shown (but not in the compressor of Figure 1). The other elements of the DRC of Figure 3 (elements 1, 3, 5 and 7) are identical to the corresponding (similarly numbered) elements of the DRC of Figure 1. The DRC gain output from the DRC gain curve subsystem 5 is identified in Figure 3 as gain "gDRC".

[0059] Elements 3, 5, 11, and 13 of Figure 3 comprise a DRC gain determination subsystem (implemented in accordance with an embodiment of the invention) that replaces conventional DRC gain determination subsystem 6 of Figure 1. In some variations of the implementation shown in Figure 3, elements 3 and 5 of Figure 3 are replaced by one of the above-described alternative implementations of DRC gain determination subsystem 6 of Figure 1.

[0060] 3 embodiment, DRC gain smoother 11 is provided to smooth the DRC gain (gDRC) output from DRC gain curve subsystem 5, thereby generating a smoothed DRC gain (identified as "gDRCsmoothed" in FIG. 3). The smoothed DRC gain and the gain gDRC (output from subsystem 5) are provided to subsystem 13. In some implementations, gain adjustment subsystem 13 is configured to output the smaller of each gain value gDRC and the corresponding smoothed gain gDRCsmoothed (as the current gain value of g(t) applied by subsystem 7), such that in response to each gain value gDRC, the output of subsystem 13 is: min(gDRC, gDRCsmoothed) It becomes.

[0061] When a segment of input audio has regular transient content (e.g., a sequence of identical or similar transient content, such as a sequence of drum hits), the smoother 11 catches up with the subsystem 5. This means that the subsystem 13 reaches a state where it outputs (i.e., provides to the subsystem 7) the current "gDRCsmoothed" value (output from the smoother 11) rather than the corresponding gain value "gDRC" output from the subsystem 5. During such operation, the application by the subsystem 7 of the gDRCsmoothed value (rather than the corresponding value gDRC) effectively delays the release of the DRC application by the system, thus reducing (or preventing the occurrence of) pumping artifacts. In a typical operation (in response to a segment of input audio having regular transient content), the subsystem 13 initially outputs the current gain value gDRC, which causes the system of FIG. 3 to operate in a state that provides some fast release behavior. This continues until a state is reached where subsystem 13 outputs the current "gDRCsmoothed" value (rather than the corresponding gDRC value), at which point the system of Figure 3 implements a slower release (i.e., implements a relatively slow release time constant), thereby reducing or preventing the occurrence of pumping artifacts. In typical operation, in response to a segment of input audio that does not have regular transient content, subsystem 13 outputs the current gain value gDRC (thus implementing a relatively fast release time constant) rather than the current "gDRCsmoothed" value.

[0062] We have found it useful to implement subsystem 13 to operate in response to a user-specified parameter p, allowing the user to trade off pumping artifacts and loudness by selecting different values ​​of parameter p (sometimes referred to as the "pumping parameter"). In such an implementation, subsystem 13 outputs a final gain g (i.e., one value of the time-varying gain g(t)) in response to each gain value gDRC and the corresponding smoothed gain gDRCsmoothed. The final gain g can be expressed as the value: g=p*gDRC+(1-p)*min(gDRC,gDRCsmoothed) where "p" is a pumping parameter with user-selectable values ​​ranging from 0 to 1.

[0063] Thus, if a user selects p to be equal to (or approximately equal to) 1, the average loudness of the output audio may be increased (compared to the average output audio loudness when p=0), but undesirable pumping artifacts may occur. If a user selects p to be equal to (or approximately equal to) 0, the average loudness of the output audio may be reduced (compared to the average output audio loudness when p=1), but the occurrence of pumping artifacts may be reduced or prevented.

[0064] In a preferred embodiment, the system of Figure 3 is implemented as a multi-band compressor. In such an implementation, the value gDRCsmooothed, and typically also the value gDRC, is determined on a band-by-band basis, allowing different choices of the pumping parameter p for different frequency bands. It may be useful to allow lower frequency bands to have larger values ​​of p.

[0065] According to some implementations of the invention, a DRC system belongs to both the first class of embodiments and the second class of embodiments. For example, a system may implement artifact reduction aspects of the second class of embodiments (e.g., its DRC gain determination subsystem may include elements 11 and 13 of the implementation of FIG. 3) and DRC reduction aspects of the first class of embodiments (e.g., it may include elements identical to or corresponding to slow smoother 2 and subsystem 4 of FIG. 2, or elements corresponding to subsystems 8 and 4 of FIG. 2A).

[0066] A third class of embodiments of the present invention is directed to reducing breathing artifacts during performance of DRC on decaying input audio. Exemplary embodiments of the third class control (e.g., include a subsystem configured to control) a release time constant (of the release of each application of dynamic range compression) in response to a loudness gradient of the input audio signal. This control typically implements a faster release time constant in response to increased steepness of the loudness gradient (to reduce or prevent the occurrence of breathing artifacts) and a slower release time constant in response to decreased steepness of the loudness gradient (to reduce or prevent the occurrence of pumping artifacts).

[0067] A third class of exemplary embodiments is described with reference to Figure 4. The dynamic range compressor of Figure 4 differs from the conventional dynamic range compressor of Figure 3 in that the compressor of Figure 4 includes a loudness gradient estimation subsystem 15 coupled as shown. The other elements of the DRC of Figure 4 (elements 1, 3, 5, 7, 11, and 13) are identical to the corresponding (same-numbered) elements of the DRC of Figure 3.

[0068] Elements 3, 5, 11, 13, and 15 of Figure 4 comprise a DRC gain determination subsystem (implemented in accordance with an embodiment of the invention) that can replace conventional DRC gain determination subsystem 6 of Figure 1. In a variation of the implementation shown in Figure 4, elements 3 and 5 of Figure 4 are replaced by one of the alternative implementations described above of DRC gain determination subsystem 6 of Figure 1.

[0069] Breathing artifacts are well-known artifacts that can result from dynamic range compression and are particularly annoying when the input audio becomes quieter (attenuates) and the DRC (dynamic range compressor) applies increasing gain to it (e.g., during the release period of the application of dynamic range compression). Depending on the relative time constants of the decaying input audio and the compressor release, breathing artifacts can result in increased loudness in the output audio at a time when the listener (or audio content creator) is expecting the audio to be getting quieter.

[0070] The averaged loudness (level or power) of the input audio signal typically varies over time and has a gradient (sometimes referred to herein as loudness gradient). The gradient is the rate of change of the averaged level or power of the input audio signal over time. In this context, the time over which the averaged loudness is determined need not be longer (or much longer) than the DRC application time mentioned above. According to an aspect of the embodiment of FIG. 4, subsystem 15 is provided for generating an estimate (e.g., a time-smoothed estimate) of the loudness gradient of the averaged loudness (average level or power) of the input audio signal. In the implementation of FIG. 4, subsystem 15 is configured to generate this loudness gradient estimate based on an estimated level or power (of the input audio signal) determined by level estimator 1. Alternatively, the loudness gradient estimate is generated in another manner (e.g., based on loudness metadata corresponding to the input audio).

[0071] The estimated level or power (of the input audio signal) determined by subsystem 1 typically varies over time, and subsystem 15 may be configured to determine for each time (from the corresponding sequence of estimated levels or powers output from subsystem 1) a time-smoothed estimate of the loudness gradient. In response to the estimate of the loudness gradient, subsystem 15 generates a control signal (identified as "CONTROL" in FIG. 4) and provides the control signal to smoother 11. In response to an increasing steepness of the loudness gradient (i.e., increasing values ​​of positive loudness gradient or increasing values ​​of negative loudness gradient (or less negative values)), the control signal generated by subsystem 15 changes the time constant of the smoothing performed by smoother 11, allowing a faster release time constant (of the release of each application of dynamic range compression by the system of FIG. 4). In other words, in response to an increasing steepness of the loudness gradient, the control signal generated by subsystem 15 varies the time constant of the smoothing performed by smoother 11, such that the smoothed gain value (gDRCsmoothed) output from smoother 11 causes subsystem 13 to output a gain value that effectively allows a faster release of the dynamic range compression application. A faster release time constant, resulting from an increasing steepness of the loudness gradient, typically reduces (or prevents the occurrence of) breathing artifacts.

[0072] In response to the decreasing steepness of the loudness gradient, the control signal generated by subsystem 15 varies the time constant of the smoothing performed by smoother 11, allowing the release time constant (of the release of each application of dynamic range compression by the system of FIG. 4) to be slower. As discussed above with reference to FIG. 3, such a slower release time constant can reduce (or prevent the occurrence of) pumping artifacts and can also reduce (or prevent the occurrence of or make less noticeable) breathing artifacts.

[0073] In a preferred embodiment, the time constant used (by smoother 11) to calculate the value gDRCsmoothed (in response to the value gDRC) is scaled by the loudness gradient (determined by subsystem 15 from the level estimates generated on the full wideband input audio) to be in the range of about 2 seconds to about 6 seconds.

[0074] In a variation of the system of Figure 4 (which is an alternative embodiment of the present invention), elements 3 and 5 of Figure 4 are replaced by an implementation of a DRC gain determination subsystem 6 (e.g., any of the implementations of subsystem 6 of Figure 2), and the control signal generated by loudness gradient estimation subsystem 15 is used to directly control (e.g., increase) the release time of such subsystem 6 rather than to control smoother 11. In such an embodiment, elements 11 and 13 are optionally omitted.

[0075] According to some embodiments of the present invention, a DRC system belongs to both the first class of embodiments and the third class of embodiments. For example, a system may implement both the artifact reduction aspects of the third class of embodiments (e.g., its DRC gain determination subsystem may include elements 11, 13, and 15 of the implementation of FIG. 4) and the DRC reduction aspects of the first class of embodiments (e.g., may include elements identical to or corresponding to slow smoother 2 and subsystem 4 of FIG. 2, or elements corresponding to subsystems 8 and 4 of FIG. 2A).

[0076] An example embodiment (EE) of the present invention includes: EE1. A method for performing dynamic range compression (DRC) on an input audio signal to generate an output audio signal, comprising: (a) determining an average loudness of an input audio signal, said average over a time period longer than a DRC application time of a DRC, said DRC application time being an attack time or a release time of an instance of application of DRC, or a duration of an instance of application of DRC; (b) applying a reduced DRC to the input audio signal when an average loudness of the input audio signal approaches, meets, or exceeds a target, thereby generating the output audio signal, and otherwise applying a full DRC to the input audio signal to generate the output audio signal. method. EE2. The method of EE1, wherein said target is an audio signal level at least substantially equal to a knee point for said DRC or a maximum playback level of a playback system or device reproducing said output audio signal. EE3. A method as described in EE1 or EE2, wherein the input audio signal has a plurality of frequency bands, and step (b) includes determining a DRC gain for each one of the frequency bands and applying the DRC gain to the each one of the frequency bands. EE4. The method of EE3, wherein step (a) includes determining a wideband average loudness of the input audio signal, and step (b) includes applying a reduced DRC to each frequency band when the wideband average loudness approaches, meets, or exceeds a target. EE5. The method of EE3, wherein step (a) includes determining an average loudness for each of the frequency bands, and step (b) includes applying the reduced DRC to each of the frequency bands whose average loudness approaches, meets, or exceeds the target. EE6. The method of EE3, wherein determining a DRC gain includes smoothing gains for individual frequency bands of the individual frequency bands across individual frequency bands of the frequency bands to improve timbre. EE7. The method of EE1, EE2, EE3, EE4, EE5, or EE6, wherein step (b) comprises: Determine the dynamic DRC gain gDRC; smoothing the dynamic DRC gain gDRC to generate a smoothed dynamic gain gDRCsmoothed; determining a dynamic gain g based on a minimum determination of the DRC gain gDRC and the smoothed dynamic gain gDRCsmoothed; applying said dynamic gain g to an input audio signal; method. EE8. The method according to claim EE7, wherein the dynamic gain g is: g=p*gDRC+(1-p)*min(gDRC,gDRCsmoothed) where "p" is a pumping parameter having a value in the range from 0 to 1. EE9. The method of EE1, EE2, EE3, EE4, EE5, EE6, EE7, or EE8, wherein the input audio signal has a loudness gradient, the method further comprising: controlling release time constants for application of the reduced DRC and the full DRC in response to a loudness gradient of the input audio signal. method. EE10. The method of EE9, wherein the release time constant is controlled to be faster in response to increased steepness of the loudness gradient and to be slower in response to decreased steepness of the loudness gradient. EE11. A method for performing dynamic range compression (DRC) on an input audio signal to generate an output audio signal, the method comprising: determining a level estimate of the input audio signal; determining a dynamic DRC gain gDRC by applying a DRC gain curve to the level estimate; smoothing the dynamic DRC gain gDRC to generate a smoothed dynamic gain gDRCsmoothed; determining a dynamic gain g based on a minimum determination of the DRC gain gDRC and the smoothed dynamic gain gDRCsmoothed; applying the dynamic gain g to an input audio signal, thereby generating the output audio signal. method. EE12.The method of claim EE11, wherein the dynamic gain g is: g=p*gDRC+(1-p)*min(gDRC,gDRCsmoothed) where "p" is a pumping parameter having a value in the range from 0 to 1. EE13. The input audio signal has a loudness gradient, and the method further comprises: controlling a release time constant for application of the DRC to the input audio signal in response to a loudness gradient of the input audio signal. The method according to claim EE11 or EE12. EE14. The method of EE13, wherein the release time constant is controlled to be faster in response to increased steepness of the loudness gradient and to be slower in response to decreased steepness of the loudness gradient. EE15. The method of EE13, wherein controlling the release time constant includes controlling a time constant for performing smoothing to generate the smoothed dynamic gain gDRCsmooothed. EE16. A method according to any one of claims 1 to 5, wherein the input audio signal has a plurality of frequency bands, and the dynamic gain g comprises individual band gains for each one of the frequency bands, and applying the dynamic gain g comprises: applying individual band gains to individual bands of a frequency band of the input audio signal; method. EE17. A system for performing dynamic range compression (DRC) on an input audio signal, comprising: a level estimation subsystem coupled and configured to determine a level estimate of the input audio signal; a DRC gain curve subsystem coupled and configured to determine a dynamic DRC gain gDRC by applying a DRC gain curve to the level estimate; a gain determination subsystem coupled and configured to smooth the dynamic DRC gain gDRC to generate a smoothed dynamic gain gDRCsmoothed, and to determine a dynamic gain g, including by determining a minimum of each pair of corresponding values ​​of the DRC gain gDRC and the smoothed dynamic gain gDRCsmoothed; a gain application subsystem coupled and configured to apply the dynamic gain g to an input audio signal to generate the output audio signal; the gain determination subsystem is configured to determine the dynamic gain g such that, when applying the dynamic gain g to a segment of the input audio signal that includes regular transient components, the system implements a first release time constant, and, when applying the dynamic gain g to a different segment of the input audio signal that does not include regular transient components, the system implements a release time constant faster than the first release time constant. system. The system according to claim EE18., wherein the dynamic gain g is: g=p*gDRC+(1-p)*min(gDRC,gDRCsmoothed) where "p" is a pumping parameter with selectable values ​​ranging from 0 to 1 in the system. EE19. The input audio signal has a loudness gradient, and the gain determination subsystem is configured to control a release time constant for application of a DRC to the input audio signal in response to the loudness gradient of the input audio signal. EE17 or EE18. EE20. The system of EE19, wherein the gain determination subsystem is configured to provide a faster release time constant in response to increased steepness of the loudness gradient and a slower release time constant in response to decreased steepness of the loudness gradient. EE21. The method of EE19, wherein the gain determination subsystem is configured to control a release time constant, including by controlling a time constant for performance of smoothing to generate the smoothed dynamic gain gDRCsmooothed. EE22. A system for performing dynamic range compression (DRC) on an input audio signal, comprising: a loudness determination subsystem coupled and configured to determine an average loudness of the input audio signal, the average over a time period longer than a DRC application time of a DRC, the DRC application time being an attack time or a release time of an instance of application of the DRC, or a duration of an instance of application of the DRC; a gain determination and application subsystem coupled and configured to apply a reduced DRC to the input audio signal when an average loudness of the input audio signal approaches, meets, or exceeds a target, thereby generating the output audio signal, and otherwise apply a full DRC to the input audio signal to generate the output audio signal. system. EE23. The system of EE22, wherein the target is an audio signal level at least substantially equal to a knee point for the DRC or a maximum playback level of a playback system or device reproducing the output audio signal. EE24. The system of EE22 or EE23, wherein the input audio signal has a plurality of frequency bands, and the gain determination and application subsystem is configured to determine a DRC gain for each one of the frequency bands and apply the DRC gain to the each one of the frequency bands. EE25. The gain determination and application subsystem: Determine the dynamic DRC gain gDRC; smoothing the dynamic DRC gain gDRC to generate a smoothed dynamic gain gDRCsmoothed; determining a dynamic gain g based on a minimum determination of the DRC gain gDRC and the smoothed dynamic gain gDRCsmoothed; configured to apply the dynamic gain g to an input audio signal. A system as described in EE22, EE23 or EE24. The system of claim EE26. EE25, wherein the dynamic gain g is: g=p*gDRC+(1-p)*min(gDRC,gDRCsmoothed) where "p" is the pumping parameter with a value ranging from 0 to 1 in the system. The system of EE27.EE22, EE23, EE24, EE25, or EE26, wherein the input audio signal has a loudness gradient, and the gain determination and application subsystem comprises: configured to control release time constants for application of the reduced DRC and the full DRC in response to a loudness gradient of the input audio signal. system. EE28. The system of EE22, EE23, EE24, EE25, EE26 or EE27, wherein the gain determination and application subsystem is configured to make the release time constant faster in response to increased steepness of the loudness gradient and slower in response to decreased steepness of the loudness gradient. Various modifications to the implementations described in this disclosure may be readily apparent to those skilled in the art. The general principles defined herein may be applied to other implementations without departing from the spirit or scope of the disclosure. Thus, the claims are not intended to be limited to the specific implementations described and shown herein, but are to be accorded the widest scope consistent with the disclosure.

[0077] The methods and systems described in this disclosure may be implemented as software, firmware and / or hardware. For example, certain components (e.g., elements 1, 2, 4, 6, and 7 of FIG. 2, or elements 1, 4, 6, 7, and 8 of FIG. 2A, or elements 1, 3, 5, 7, 11, and 13 of FIG. 3, or elements 1, 3, 5, 7, 11, 13, and 15 of FIG. 4) may be implemented as software running on a digital signal processor (e.g., having an input coupled to receive an input audio signal) or a microprocessor. Some components may be implemented as hardware and / or as application specific integrated circuits. The signals encountered in the above-described methods and systems may be stored in a medium such as a random access memory or an optical storage medium. They may be transferred over a network such as an airwave network, a satellite network, a wireless network, or a wired network such as the Internet. A typical device utilizing the methods and systems described in this disclosure is a portable electronic device or other consumer equipment used to store and process (e.g., implement playback or render) an audio signal (e.g., an output audio signal generated according to any embodiment of the system or method of the present invention).

[0078] In this application, a reference in the form "A and / or B" means "A" or "B" or "A and B."

[0079] Several aspects will be described. [Aspect 1] 1. A method for performing dynamic range compression (DRC) on an input audio signal to generate an output audio signal, comprising: (a) determining an average loudness of the input audio signal, loudness representing a level or power of the input audio signal, said average over a time longer than a DRC application time of the DRC, the DRC application time being an attack time or a release time of an instance of application of the DRC, or a duration of an instance of application of the DRC including an attack and a release, that applies a non-unity gain after an attack and before a release, or where a DRC gain curve determines a non-unity gain; (b) applying a reduced DRC to the input audio signal when the average loudness of the input audio signal approaches, meets or exceeds a target, thereby generating the output audio signal, and otherwise applying a full DRC to the input audio signal to generate the output audio signal, wherein the target is an audio signal level at least substantially equal to a knee point for the DRC or a maximum playback level of a playback system or device that reproduces the output audio signal. method. [Aspect 2] 2. The method of claim 1, wherein the input audio signal has multiple frequency bands. [Aspect 3] 3. The method of claim 2, wherein step (b) comprises determining a DRC gain for at least one frequency band of the plurality of frequency bands and applying the DRC gain to the frequency band. Aspect 4 3. The method of claim 2, wherein step (b) comprises determining DRC gains for each one of the frequency bands and applying those DRC gains to the each one of the frequency bands. Aspect 5 5. The method of claim 4, wherein determining the DRC gains includes smoothing gains for individual frequency bands of the frequency band across individual frequency bands of the frequency band to improve timbre. Aspect 6 3. The method of claim 2, wherein step (a) includes determining a wideband average loudness of the input audio signal, and step (b) includes applying the reduced DRC to each frequency band when the wideband average loudness approaches, meets, or exceeds a target. Aspect 7 3. The method of claim 2, wherein step (a) includes determining an average loudness for each of the frequency bands, and step (b) includes applying the reduced DRC to each frequency band whose average loudness approaches, meets, or exceeds the target. Aspect 8 Stage (b) is: Determine the dynamic DRC gain gDRC; smoothing the dynamic DRC gain gDRC to generate a smoothed dynamic gain gDRCsmoothed; determining a dynamic gain g based on a minimum determination of the DRC gain gDRC and the smoothed dynamic gain gDRCsmoothed; applying the dynamic gain g to the input audio signal. 8. The method according to any one of embodiments 1 to 7. Aspect 9 9. The method of claim 8, wherein the dynamic gain g is: g=p*gDRC+(1-p)*min(gDRC,gDRCsmoothed) where "p" is a pumping parameter having a value in the range from 0 to 1. Aspect 10 10. The method of claim 9, wherein a value of the pumping parameter within the range of 0 to 1 is user selectable. Aspect 11 The input audio signal has a loudness gradient, the method further comprising: controlling release time constants for application of the reduced DRC and a full DRC in response to the loudness gradient of the input audio signal. 11. The method according to any one of embodiments 1 to 10. Aspect 12 12. The method of claim 11, wherein the release time constant is controlled to be faster in response to an increased steepness of the loudness gradient and to be slower in response to a decreased steepness of the loudness gradient. Aspect 13 1. A method for performing dynamic range compression (DRC) on an input audio signal to generate an output audio signal, the method comprising: determining a level estimate of the input audio signal; determining a dynamic DRC gain gDRC by applying a DRC gain curve to the level estimate; smoothing the dynamic DRC gain gDRC to generate a smoothed dynamic gain gDRCsmoothed; determining a dynamic gain g based on a minimum determination of the DRC gain gDRC and the smoothed dynamic gain gDRCsmoothed; applying the dynamic gain g to the input audio signal, thereby generating the output audio signal. method. Aspect 14 14. The method of claim 13, wherein the dynamic gain g is: g=p*gDRC+(1-p)*min(gDRC,gDRCsmoothed) where "p" is a pumping parameter having a value in the range from 0 to 1. Aspect 15 15. The method of claim 14, wherein the value of the pumping parameter in the range of 0 to 1 is user selectable. Aspect 16 The input audio signal has a loudness gradient, the method further comprising: controlling a release time constant for application of a DRC to the input audio signal in response to the loudness gradient of the input audio signal. 16. The method according to any one of embodiments 13 to 15. Aspect 17 17. The method of embodiment 16, wherein the release time constant is controlled to be faster in response to an increased steepness of the loudness gradient and controlled to be slower in response to a decreased steepness of the loudness gradient. Aspect 18 Aspect 16. The method of aspect 16, wherein controlling the release time constant includes controlling a time constant for performing smoothing to generate the smoothed dynamic gain gDRCsmooothed. Aspect 19 19. The method of any one of aspects 13 to 18, wherein the input audio signal has a plurality of frequency bands, and the dynamic gain g comprises individual band gains for respective ones of the frequency bands, and applying the dynamic gain g comprises: applying said individual band gains to individual bands of frequency bands of the input audio signal. method. Aspect 20 1. A system for performing dynamic range compression (DRC) on an input audio signal, comprising: a level estimation subsystem coupled and configured to determine a level estimate of the input audio signal; a DRC gain curve subsystem coupled and configured to determine a dynamic DRC gain gDRC by applying a DRC gain curve to the level estimate; a gain determination subsystem coupled and configured to smooth the dynamic DRC gain gDRC to generate a smoothed dynamic gain gDRCsmoothed, and to determine a dynamic gain g, including by determining a minimum of each pair of corresponding values ​​of the DRC gain gDRC and the smoothed dynamic gain gDRCsmoothed; a gain application subsystem coupled and configured to apply the dynamic gain g to the input audio signal, thereby generating the output audio signal; the gain determination subsystem is configured to determine the dynamic gain g such that when applying the dynamic gain g to a segment of the input audio signal that includes regular transient components, the system implements a first release time constant, and when applying the dynamic gain g to a different segment of the input audio signal that does not include regular transient components, the system implements a release time constant faster than the first release time constant. system. Aspect 21 21. The system of claim 20, wherein the dynamic gain g is: g=p*gDRC+(1-p)*min(gDRC,gDRCsmoothed) where "p" is a pumping parameter with selectable values ​​ranging from 0 to 1 in the system. Aspect 22 22. The system of claim 21, wherein the value of the pumping parameter within the range of 0 to 1 is user selectable. Aspect 23 the input audio signal has a loudness gradient, and the gain determination subsystem is configured to control a release time constant for application of a DRC to the input audio signal in response to the loudness gradient of the input audio signal. The system according to embodiment 20 or embodiment 22. Aspect 24 24. The system of claim 23, wherein the gain determination subsystem is configured to make the release time constant faster in response to an increased steepness of the loudness gradient and to make the release time constant slower in response to a decreased steepness of the loudness gradient. Aspect 25 24. The system of claim 23, wherein the gain determination subsystem is configured to control the release time constant, including by controlling a time constant for performing smoothing to generate the smoothed dynamic gain gDRCsmooothed. Aspect 26 1. A system for performing dynamic range compression (DRC) on an input audio signal, comprising: a loudness determination subsystem coupled and configured to determine an average loudness of the input audio signal, the loudness representing a level or power of the input audio signal, the average being over a time longer than a DRC application time of the DRC, the DRC application time being an attack time or a release time of an instance of application of the DRC, or a duration of an instance of application of the DRC including an attack and a release, that applies a non-unity gain after an attack and before a release, or where a DRC gain curve determines a non-unity gain; and a gain determination and application subsystem coupled and configured to apply a reduced DRC to the input audio signal when an average loudness of the input audio signal approaches, meets or exceeds a target, thereby generating the output audio signal, and otherwise apply a full DRC to the input audio signal to generate the output audio signal, wherein the target is an audio signal level at least substantially equal to a knee point for the DRC or a maximum playback level of a playback system or device that reproduces the output audio signal. system. Aspect 27 27. The system of embodiment 26, wherein the input audio signal has multiple frequency bands. Aspect 28 28. The system of aspect 27, wherein the gain determination and application subsystem is configured to determine a DRC gain for at least one frequency band among the plurality of frequency bands and apply the DRC gain to the frequency band. Aspect 29 28. The system of embodiment 27, wherein the gain determination and application subsystem is configured to determine DRC gains for individual ones of the frequency bands and apply those DRC gains to the individual ones of the frequency bands. Aspect 30 30. The system of claim 29, wherein determining the DRC gain includes smoothing gains for individual frequency bands of the frequency band across individual frequency bands of the frequency band to improve timbre. Aspect 31 28. The system of claim 27, wherein the gain determination and application subsystem is configured to determine a wideband average loudness of the input audio signal and apply the reduced DRC to each frequency band when the wideband average loudness approaches, matches, or exceeds the target. Aspect 32 28. The system of claim 27, wherein the gain determination and application subsystem determines an average loudness for each of the frequency bands and applies the reduced DRC to each frequency band whose average loudness approaches, matches, or exceeds the target. Aspect 33 The gain determination and application subsystem: Determine the dynamic DRC gain gDRC; smoothing the dynamic DRC gain gDRC to generate a smoothed dynamic gain gDRCsmoothed; determining a dynamic gain g based on a minimum determination of the DRC gain gDRC and the smoothed dynamic gain gDRCsmoothed; configured to apply the dynamic gain g to the input audio signal. A system described in any one of aspects 26 to 32. Aspect 34 34. The system of claim 33, wherein the dynamic gain g is: g=p*gDRC+(1-p)*min(gDRC,gDRCsmoothed) where "p" is the pumping parameter with a value ranging from 0 to 1 in the system. Aspect 35 35. The system of embodiment 34, wherein the value of the pumping parameter within the range of 0 to 1 is user selectable. Aspect 36 The input audio signal has a loudness gradient, and the gain determination and application subsystem: configured to control release time constants for application of the reduced DRC and a full DRC in response to the loudness gradient of the input audio signal. A system described in any one of aspects 26 to 35. Aspect 37 37. The system of embodiment 36, wherein the gain determination and application subsystem is configured to make the release time constant faster in response to an increased steepness of the loudness gradient and slower in response to a decreased steepness of the loudness gradient. Aspect 38 37. The system of embodiment 36, wherein controlling the release time constant includes controlling a time constant for performing smoothing to generate the smoothed dynamic gain gDRCsmoothed.

Claims

1. 1. A method for performing dynamic range compression (DRC) on an input audio signal to generate an output audio signal, comprising: (a) determining an average loudness of the input audio signal, loudness representing a level or power of the input audio signal, the average loudness being determined over a time longer than a DRC application time of the DRC, the DRC application time being an attack time or a release time of an instance of application of the DRC that applies a non-unity gain or where a DRC gain curve determines a non-unity gain after an attack time and before a release time, or a duration of an instance of application of the DRC that includes the attack time and the release time; (b) applying a reduced DRC to the input audio signal to generate the output audio signal by controlling a DRC gain to approach a gain of 1 when the average loudness of the input audio signal approaches, meets, or exceeds a target, and otherwise applying the DRC gain to the input audio signal to generate the output audio signal, wherein the target is a knee point for the DRC. method.

2. The method of claim 1 , wherein the input audio signal comprises multiple frequency bands.

3. The method of claim 2 , wherein step (b) comprises determining a DRC gain for at least one frequency band of the plurality of frequency bands and applying the DRC gain to the frequency band.

4. 3. The method of claim 2, wherein step (b) comprises determining DRC gains for each one of the frequency bands and applying those DRC gains to the each one of the frequency bands.

5. 5. The method of claim 4, wherein determining the DRC gains comprises smoothing gains for individual frequency bands of the frequency bands across individual frequency bands of the frequency bands to improve timbre.

6. 3. The method of claim 2, wherein step (a) includes determining a wideband average loudness of the input audio signal, and step (b) includes applying the reduced DRC to each frequency band when the wideband average loudness approaches, meets, or exceeds a target.

7. 3. The method of claim 2, wherein step (a) includes determining a respective average loudness for each of the frequency bands, and step (b) includes applying the reduced DRC to each frequency band whose average loudness approaches, meets, or exceeds the target.

8. Stage (b) is: determining a DRC gain gDRC; smoothing the DRC gain gDRC to generate a smoothed dynamic gain gDRCsmoothed; generating a dynamic gain g, where if the DRC gain gDRC is less than the smoothed dynamic gain gDRCsmoothed, then the dynamic gain g is the DRC gain gDRC, otherwise the dynamic gain g is a weighted average of gDRC and gDRCsmoothed; applying the dynamic gain g to the input audio signal. The method of claim 1.

9. 9. The method of claim 8, wherein the dynamic gain g is: g=p*gDRC+(1-p)*min(gDRC,gDRCsmoothed) where "p" is a pumping parameter having a value in the range from 0 to 1.

10. The method of claim 9 , wherein the value of the pumping parameter in the range of 0 to 1 is user selectable.

11. The input audio signal has a loudness gradient, the method further comprising: controlling release time constants for application of the reduced DRC and a full DRC in response to the loudness gradient of the input audio signal. The method of claim 1.

12. 12. The method of claim 11, wherein the release time constant is controlled to be faster in response to an increased steepness of the loudness gradient and is controlled to be slower in response to a decreased steepness of the loudness gradient.

13. 1. A method for performing dynamic range compression (DRC) on an input audio signal to generate an output audio signal, the method comprising: determining a level estimate of the input audio signal; determining a DRC gain gDRC by applying a DRC gain curve to the level estimate; smoothing the DRC gain gDRC to generate a smoothed dynamic gain gDRCsmoothed; generating a dynamic gain g, where if the DRC gain gDRC is less than the smoothed dynamic gain gDRCsmoothed, then the dynamic gain g is the DRC gain gDRC, otherwise the dynamic gain g is a weighted average of gDRC and gDRCsmoothed; and applying the dynamic gain g to the input audio signal, thereby generating the output audio signal. method.

14. 14. The method of claim 13, wherein the dynamic gain g is: g=p*gDRC+(1-p)*min(gDRC,gDRCsmoothed) where "p" is a pumping parameter having a value in the range from 0 to 1.

15. The method of claim 14 , wherein the value of the pumping parameter in the range of 0 to 1 is user selectable.

16. The input audio signal has a loudness gradient, the method further comprising: controlling a release time constant for application of a DRC to the input audio signal in response to the loudness gradient of the input audio signal. The method of claim 13.

17. 17. The method of claim 16, wherein the release time constant is controlled to be faster in response to an increased steepness of the loudness gradient and is controlled to be slower in response to a decreased steepness of the loudness gradient.

18. Claim 16. The method of claim 16, wherein controlling the release time constant comprises controlling a time constant for performing smoothing to generate the smoothed dynamic gain gDRCsmooothed.

19. 14. The method of claim 13, wherein the input audio signal has a plurality of frequency bands, and the dynamic gain g comprises individual band gains for each one of the frequency bands, and applying the dynamic gain g comprises: applying said individual band gains to individual bands of frequency bands of the input audio signal. method.

20. 1. A system for performing dynamic range compression (DRC) on an input audio signal, comprising: a level estimation subsystem coupled and configured to determine a level estimate of the input audio signal; a DRC gain curve subsystem coupled and configured to determine a dynamic DRC gain gDRC by applying a DRC gain curve to the level estimate; a gain determination subsystem coupled and configured to smooth the dynamic DRC gain gDRC to generate a smoothed dynamic gain gDRCsmoothed, and to determine a dynamic gain g, including by determining a minimum of each pair of corresponding values ​​of the DRC gain gDRC and the smoothed dynamic gain gDRCsmoothed; a gain application subsystem coupled and configured to apply the dynamic gain g to the input audio signal, thereby generating the output audio signal; the gain determination subsystem is configured to determine the dynamic gain g such that when applying the dynamic gain g to a segment of the input audio signal that includes regular transient components, the system implements a first release time constant, and when applying the dynamic gain g to a different segment of the input audio signal that does not include regular transient components, the system implements a release time constant faster than the first release time constant. system.

21. 1. A system for performing dynamic range compression (DRC) on an input audio signal, comprising: a loudness determination subsystem coupled and configured to determine an average loudness of the input audio signal, where loudness represents a level or power of the input audio signal, and where the average loudness is determined over a time period that is longer than a DRC application time of the DRC, where the DRC application time is an attack time or a release time of an instance of application of the DRC that applies a non-unity gain or where a DRC gain curve determines a non-unity gain after an attack time and before a release time, or a duration of an instance of application of the DRC that includes the attack time and the release time; a gain determination and application subsystem coupled and configured to apply a reduced DRC to the input audio signal to generate the output audio signal by controlling a DRC gain to approach a gain of 1 when the average loudness of the input audio signal approaches, meets, or exceeds a target, and to otherwise apply the DRC gain to the input audio signal to generate the output audio signal, wherein the target is a knee point for the DRC. system.

22. 22. The system of claim 21, wherein the input audio signal comprises multiple frequency bands.

23. 23. The system of claim 22, wherein the gain determination and application subsystem is configured to determine a DRC gain for at least one frequency band of the plurality of frequency bands and apply the DRC gain to the frequency band.

24. 23. The system of claim 22, wherein the gain determination and application subsystem is configured to determine DRC gains for respective ones of the frequency bands and apply those DRC gains to the respective ones of the frequency bands.

25. 25. The system of claim 24, wherein determining the DRC gains includes smoothing gains for individual frequency bands of the frequency bands across individual frequency bands of the frequency bands to improve timbre.

26. 23. The system of claim 22, wherein the gain determination and application subsystem is configured to determine a wideband average loudness of the input audio signal and apply the reduced DRC to each frequency band when the wideband average loudness approaches, meets, or exceeds the target.

27. 23. The system of claim 22, wherein the gain determination and application subsystem includes determining a respective average loudness for each of the frequency bands and applying the reduced DRC to each frequency band whose average loudness approaches, meets, or exceeds the target.

Images