SYSTEM FOR REDUCING MECHANICAL RATTLING OR ClatterING NOISES

Abstract

A computer comprising a system for reducing mechanical rattling or clattering noises resulting from a mechanical coupling of an audio output converter to a part of the computer device, wherein the system comprises: a processing subsystem configured to receive an input audio signal and to output a drive signal to drive the audio output converter in order to generate a converter output, wherein the processing subsystem is configured to selectively apply an attenuation function to the input audio signal in order to attenuate a signal component of the input audio signal at a frequency that causes mechanical rattling or clattering noises in the computer;and an analyzer subsystem configured to receive the input audio signal and output a control signal to the processing subsystem to control the application of the attenuation function to the input audio signal by the processing subsystem based on a spectral content of the received input audio signal; wherein the attenuation function is based on a characteristic acoustic behavior of the computer.

Description

Field of invention The present disclosure relates to a system for reducing mechanical rattling or clattering noises, for example in a computer, such as a laptop or tablet computer or an all-in-one desktop computer. The present disclosure further relates to a computer, such as a laptop or tablet computer or an all-in-one desktop computer, which includes a system for reducing mechanical rattling or clattering noises. background Computer devices such as laptop computers, tablet computers, and all-in-one desktop computers typically have one or more sound transducers (for example, loudspeakers) for generating audible output from the device's audio system. The sound transducer(s) are usually mechanically coupled to (for example, mounted to) a part of the device, such as a frame, chassis, enclosure, or housing. Due to size, design, and manufacturing limitations, these loudspeaker mounting configurations typically result in low-frequency energy in the audio spectrum of the sound emitted by the transducer being transferred directly into the frame, chassis, enclosure, or housing of the device with minimal attenuation. Depending on the spectral content of a signal output to the transducer by the audio system, this escape of energy from the transducer can cause mechanical resonance of the entire device or of a part of the device to which the transducer is mechanically coupled, thereby generating secondary noise. One result of this mechanical resonance is an audible distortion (which may be described as a mechanical rattle or clattering noise) that may impair a user's experience of the device and may reduce the acoustic fidelity of the transducer's output. Systems have been developed to reduce distortion caused by a loudspeaker. Such systems can employ a masking regime to reduce the mid-band frequency content in an audio signal transmitted to the loudspeaker when the high-frequency content is low compared to the mid-band frequency. These systems generally apply time-domain analysis and attenuate a wide range of frequencies, which can be selected based on arbitrary and subjective tuning. However, such mid-band attenuation can be perceived by a listener as a significant reduction in volume. Furthermore, any masking content that might be added to the audio signal to mask distortion can be perceived by a listener as an undesirable coloration of the sound. Furthermore, while such systems can reduce or mask distortion caused by the loudspeaker itself, they do not solve the problem of mechanical resonance or rattling or clattering noises caused by the mechanical coupling of a sound output transducer (for example, a loudspeaker) with part of a host device, such as a computer device. Brief description According to a first aspect, the invention provides a computer comprising a system for reducing mechanical rattling or clattering noises caused by the mechanical coupling of an audio output converter to a part of the computer device, wherein the system comprises: a processing subsystem configured to receive an input audio signal and to output a drive signal for controlling the audio output converter to generate a converter output, wherein the processing subsystem is configured to selectively apply an attenuation function to the input audio signal in order to attenuate a signal component of the input audio signal at a frequency that causes mechanical rattling or clattering noises in the computer;and an analyzer subsystem configured to receive the input audio signal and output a control signal to the processing subsystem to control the application of the attenuation function to the input audio signal by the processing subsystem based on a spectral content of the received input audio signal; wherein the attenuation function is based on a characteristic acoustic behavior of the computer. The processing subsystem can further be configured to selectively apply an amplification function to the input audio signal in order to boost a signal component of the input audio signal at a frequency that masks an effect of mechanical rattling or clattering noises in the computer device. The analyzer subsystem may include a classifier configured to classify the input audio signal into one or more classes based on the spectral content of the input audio signal and to output a control signal to the processing subsystem to control the application of the attenuation function to the input audio signal by the processing subsystem based on the classification of the input audio signal. The classifier may include a neural network or a machine learning model trained to identify features of the input audio signal that are characteristic of each of the one or more classes, and to classify the input audio signal based on the identified features of the input audio signal. The classifier can comprise a neural network or a machine learning model trained to identify features of the input audio signal that are characteristic of each of the one or more classes. The classifier can be configured to determine a measure in relation to identified features of the input audio signal and to classify the input audio signal based on this measure. The analyzer subsystem can be configured to output the control signal in response to the detection of a spectral content in the input audio signal at a level above a rattle or clatter noise threshold at a frequency that could lead to mechanical rattle or clatter noises in the computer device. The analyzer subsystem can be configured to determine a first ratio of high-frequency content to low-frequency content of the input audio signal and / or a second ratio of low-frequency content to high-frequency content of the input audio signal and to output a control signal to the processing block to control the application of the attenuation function based on the determined first and / or second ratio. The analyzer subsystem can be configured to perform a Fast Fourier Transform (FFT) of the input audio signal to generate a frequency domain representation of the input audio signal received by the analyzer block. The analyzer subsystem can be configured to output the control signal in response to the detection of a signal spike in the frequency domain representation of the input audio signal at a frequency that could cause mechanical rattling or clattering noises in the computer device. The analyzer subsystem can be configured to output the control signal in response to the detection of a signal peak in the frequency domain representation of the input audio signal at a level above a rattle or clatter noise threshold at a frequency that could lead to mechanical rattle or clatter noises in the computer device. The analyzer subsystem can be configured to determine the ratio of a level of a detected high-frequency signal peak in the frequency domain representation of the input audio signal to a level of a detected low-frequency signal peak in the frequency domain representation and to output the control signal if the determined ratio exceeds a frequency content ratio threshold. The analyzer subsystem can be configured to prevent the processing subsystem from applying the damping function in response to the detection of a spectral content in the input audio signal at a frequency that might mask mechanical rattle or clatter noises in the computer. The analyzer subsystem can be configured to prevent the processing subsystem from applying the damping function in response to the detection of a spectral content in the input audio signal at a level above a rattle or clatter masking threshold at a frequency that could mask mechanical rattle or clatter noises in the computer. The analyzer subsystem can be configured to output a control signal to cause the processing subsystem to apply the gain function in response to the detection of a spectral content in the input audio signal at a frequency that might mask mechanical rattle or clatter noises in the computer. The input audio signal can be a digital signal comprising multiple frames. The analyzer subsystem can be configured to output a control signal to the processing subsystem for each frame of the input audio signal, based on the frame's spectral content, to control the application of the attenuation function or to prevent the processing subsystem from applying the attenuation function. The processing subsystem can include one or more filters configured to implement the damping function. Each or every filter can include a narrowband filter. The filter(s) may include a dynamically reconfigurable filter with a controllable transfer function. The processing subsystem may be configured to control the transfer function of the dynamically reconfigurable filter(s) based on a control signal received from the analyzer subsystem. Each filter can be a time domain filter or a frequency domain filter. The processing subsystem can be configured to selectively apply one or more masks to the input audio signal based on the classification performed by the classifier. Each mask can be configured to implement an attenuation function to reduce the spectral content in the input audio signal that causes rattling or popping noises, thereby optimizing or improving a characteristic of the converter output signal. The processing system can be configured to apply a first mask in response to a classification of the audio input signal as music, in order to optimize or improve the fidelity of the converter output, and to apply a second mask in response to a classification of the audio input signal as speech, in order to optimize or improve the intelligibility of the converter output. The computer may include an input converter. The processing subsystem may be configured to: receive a feedback signal from the input converter; detect distortion in the converter output based on the feedback signal; and, in response to the detection of distortion in the converter output, apply an attenuation function and / or a gain function to the audio input signal. The processing subsystem can be configured to monitor one or more of the transducer output sound pressure level and baseband content and associated harmonics based on the feedback signal in order to detect distortions in the transducer output. The processing subsystem can be configured to apply the damping function according to an attack / release function. The processing subsystem can be configured to progressively apply the damping function to the audio input signal over a period of time from a minimum damping level to a maximum damping level, such that the maximum damping level is applied to a spectral content of the audio input signal at a frequency that could lead to mechanical rattling or clattering noises in the computer device. The processing subsystem can be configured to selectively apply the damping function in the time domain or in the frequency domain based on the classification of the input signal by the classifier. The processing subsystem can be configured to apply the attenuation function in the time domain in response to a classification of the audio input signal as speech, and to apply the attenuation function in the frequency domain in response to a classification of the audio input signal as music. The processing subsystem can be configured to selectively apply the damping function in the time domain or in the frequency domain based on the identification of features of the audio input signal by the analyzer subsystem. The processing subsystem can be configured to apply the attenuation function in the time domain in response to the identification of features in the audio input signal indicating that the audio input signal represents speech, and to apply the attenuation function in the frequency domain in response to the identification of features in the audio input signal indicating that the audio input signal represents music. The computer can be, for example, a laptop computer, a tablet computer, or an all-in-one desktop computer. According to a second aspect, the invention provides a method for evaluating the characteristic acoustic behavior of a computer comprising an audio output converter, wherein the method comprises the following steps: supplying a stimulus signal to the audio output converter; monitoring the computer to detect a mechanical resonance effect in the computer; and generating a distortion frequency profile for the computer based on a frequency and amplitude of the stimulus signal for which a mechanical resonance effect was detected in the computer device. Monitoring the computer device to detect a mechanical resonance effect can be done using an input converter of the computer. The stimulus signal can comprise several tones that are spaced apart in their frequency. According to a third aspect, the invention provides a system for reducing mechanical rattling or clattering noises in a computer that arise due to a mechanical coupling of an audio output converter with a part of the computer, wherein the system comprises: a processing subsystem configured to receive an input audio signal and to output a drive signal to control the audio output converter in order to generate a converter output, wherein the processing subsystem is configured to selectively apply an attenuation function to the input audio signal in order to attenuate a signal component of the input audio signal at a frequency that causes mechanical rattling or clattering noises in the computer, wherein the attenuation function is based on a characteristic acoustic behavior of the computer. According to a fourth aspect, the invention provides a system for reducing mechanical rattling or clattering noises in a computer that arise due to a mechanical coupling of an audio transducer with a part of the computer, wherein the system comprises: a classifier subsystem configured to classify the audio input signal into one or more of several classes; and a processing block configured to selectively apply an attenuation function to the input signal in order to attenuate a signal component of the audio input signal according to the classification of the audio input signal. According to a fifth aspect, the invention provides a system for reducing mechanical rattling or clattering noises in a computer that arise due to a mechanical coupling of an audio transducer with a part of the computer, wherein the system comprises: a classifier subsystem configured to classify the audio input signal into one or more of several classes; and a processing block configured to apply one of several attenuation functions to the input signal in order to attenuate a signal component of the audio input signal, wherein the processing block is configured to select the attenuation function based on the classification of the audio input signal. According to a sixth aspect, the invention provides a system for reducing mechanical rattling or clattering noises in a computer that arise due to a mechanical coupling of an audio transducer with a part of the computer, wherein the system comprises: a classifier subsystem configured to classify the audio input signal into one or more of several classes; and a processing block configured to selectively apply an attenuation function to the input signal in order to attenuate a signal component of the audio input signal, wherein the processing block is configured to apply either a frequency domain attenuation function or a time domain attenuation function according to the classification of the audio input signal. According to a seventh aspect, the invention provides a system for reducing mechanical resonances in a host device that occur due to a mechanical coupling of an audio output converter with a part of the host device, wherein the system comprises: a processing subsystem configured to receive an input audio signal and output a drive signal to drive the audio output converter in order to generate a converter output, wherein the processing subsystem is configured to selectively apply an attenuation function to the input audio signal in order to attenuate a signal component of the input audio signal at a frequency that causes mechanical resonance in the host device. According to an eighth aspect, the invention provides an integrated circuit that implements the system according to one of the third to seventh aspects. The integrated circuit may include an integrated circuit designed as a smart amplifier. According to a ninth aspect, the invention provides a host device comprising the system according to one of the third to seventh aspects. The host device may include, for example, a laptop, notebook, netbook or tablet computer, an all-in-one computer, a gaming device, a game console, a game console controller, a virtual reality device (VR device) or augmented reality device (AR device), a mobile phone, a portable audio player, a portable device, an accessory for use with a laptop, notebook, netbook or tablet computer, a gaming device, a game console, a VR or AR device, a mobile phone, a portable audio player or any other portable device, or a vehicle. Throughout this entire specification, the word "include" or variations such as "includes" or "comprehensive" shall be understood to imply the inclusion of any named element, integer, or step, or group of elements, integers, or steps, but not the exclusion of any other elements, integers, or steps, or groups of elements, integers, or steps. Brief description of the drawings Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, which show the following: Fig. 1 is a diagram illustrating the principle of reducing mechanical resonance in an audio system of a host device according to the present disclosure; Fig. 2 is a diagram of an example of a subsystem for reducing mechanical resonance; Fig. 3 is a diagram of an example of a subsystem for reducing mechanical resonance, showing details of an analyzer block; Fig. 4 is a diagram of an example of a subsystem for reducing mechanical resonance, showing details of an alternative analyzer block; Fig. 5 is a diagram of an example of a subsystem for reducing mechanical resonance, showing details of a processing block; Fig.Figure 6 is a diagram of an example of a mechanical resonance mitigation subsystem, showing details of an alternative processing block; Figure 7 is a diagram of another example of a mechanical resonance mitigation subsystem; Figure 8 is a diagram of an example of a mechanical resonance mitigation subsystem with a feedback arrangement; and Figure 9 is a flowchart showing steps in a method for determining or evaluating the characteristic behavior of a host device for a mechanical resonance subsystem of the type illustrated in Figures 2, 3, 4, 5, 6, 7 to 8. Detailed description Fig. 1 is a diagram illustrating the principle of reducing mechanical resonance or rattling or clattering noises in an audio system of a host device according to one aspect of the present disclosure. As shown in Fig. 1, a host device 100, such as a laptop, tablet or all-in-one desktop computer, comprises one or more audio output converters 110, such as loudspeakers, and an audio system 120 configured to generate an audio signal to drive the audio output converter 110 to produce an audible output. The audio output converter 110 is mechanically coupled to a part of the host device 100, for example a frame, chassis, enclosure or housing of the host device 100 (for example mounted or attached to it). The audio signal generated by the Audio System 120 can, for example, represent speech from an audio or video telephony software application running on the Host Device 100, music from a music player application running on the Host Device 100, or sound effects and / or speech and / or music from a game or video player application running on the Host Device 100. The audio signal can be a digital audio signal or an analog signal. A digital audio signal can comprise multiple frames of audio data, with each frame comprising one or more samples of an analog audio signal. As noted above, the mounting arrangement of the audio output converter 110 may cause mechanical rattling or clattering noises resulting from mechanical resonance of the host device 100 (or part of the host device 100) when an audio signal containing a signal content at certain frequencies is transmitted to the audio output converter 110. To reduce or mitigate the problem of mechanical rattling or clattering noises, the host device 100 includes a subsystem 130 for reducing mechanical rattling or clattering noises. Although shown separately from the audio system 120 in Fig. 1, the subsystem 130 for reducing mechanical rattling or clattering noises can form part of the audio system 120 of the host device 100. Alternatively, the subsystem 130 for reducing mechanical rattling or clattering noises can be an independent subsystem of the host device 100.The subsystem 130 for reducing mechanical rattling or clattering noises can be implemented in hardware (for example, as one or more integrated circuits or as a discrete circuit), or it can be implemented in software running on appropriately configured hardware (for example, firmware running on an integrated circuit (IC) or IC block designed as a digital signal processor, a smart amplifier IC or IC block, or the like). Subsystem 130 for reducing mechanical rattle or clatter noises is configured to receive an audio signal output by audio system 120 and selectively apply an attenuation function to this input audio signal to generate a drive signal to be output to audio output converter 110 to produce an audible output. The attenuation function applies frequency-specific attenuation to the received input audio signal to attenuate signal components of the input audio signal at one or more frequencies that cause mechanical rattle or clatter noises in the host device 100. Additionally or alternatively, subsystem 130 for reducing mechanical rattle or clatter noises can also be configured to selectively apply an amplification function to the input audio signal to generate the drive signal.The amplification function boosts signal components of the input audio signal at frequencies that mask mechanical rattle or clatter noises in the host device 100. The attenuation function can be implemented, for example, by one or more filters contained in or implemented by subsystem 130 for reducing mechanical rattle or clatter noises. The amplification function can be implemented by controlling the gain of one or more of the filters. A damping function and / or a gain function can be selectively applied frame by frame to the input audio signal by subsystem 130 to reduce mechanical rattle or clatter noises, such that different damping functions can be applied to different frames of the input audio signal. For example, for an audio signal comprising a first, a second, and a third frame, a first damping function and / or gain function can be applied to the first frame, a second damping function and / or gain function (different from the first damping function and / or gain function) can be applied to the second frame, and no damping function needs to be applied to the third frame (but a gain function can be applied to the third frame). Fig. 2 is a diagram of an example of a subsystem 130 for reducing mechanical rattling or clattering noises, suitable for use in the host device 100 of Fig. 1. In the example shown in Fig. 2, the subsystem 130 for reducing mechanical rattle or clatter noises comprises an analyzer block or analyzer subsystem 210 and a processing block or processing subsystem 220. The analyzer block 210 and the processing block 220 can each be implemented in hardware (for example, in one or more integrated circuits or in a discrete circuit) or can be implemented in software running on appropriately configured hardware (for example, firmware running on an integrated circuit (IC) or IC block implemented as a digital signal processor, a smart amplifier IC or IC block, or the like).In a specific example, the analyzer block 210 and the processing block 220 are both implemented in software or firmware executed by a digital signal processor (DSP) or an integrated circuit (IC) or IC block designed as an intelligent amplifier. The analyzer block 210 is configured to receive an input audio signal from an audio system of a host device (for example, the audio system 120 of the host device 100 of Fig. 1), to analyze the spectral content of the received input audio signal, and to output a control signal to the processing block 220 to control processing applied by the processing block 220 to the input audio signal based on the spectral content of the received input audio signal. The analyzer block 210 is designed to detect a spectral content in the input audio signal at one or more frequencies or frequency bands that may cause mechanical rattling or clattering noises in the special host device into which the audio output converter 110 is integrated. In some examples, analyzer block 210 is configured to output a control signal to processing block 220 if a spectral content at a frequency causing rattle or clatter is detected in the input audio signal. In other examples, analyzer block 210 is configured to compare a level (for example, an amplitude) of the detected spectral content at a frequency causing rattle or clatter with a first rattle or clatter threshold and only output a control signal to processing block 220 if the level of the detected spectral content at the frequency causing rattle or clatter is greater than the first rattle or clatter threshold. Depending on the characteristics and / or configuration of the host device 100, the spectral content of the input audio signal at two or more frequencies or frequency bands could lead to mechanical rattling or clattering noises in the host device 100. In such cases, the level of the spectral content in the input audio signal at a first frequency or frequency band that leads to mechanical rattling or clattering noises may differ from the level of the spectral content at a second frequency or frequency band that leads to mechanical rattling or clattering noises.Thus, the analyzer block 210 can be configured to compare the level of the spectral content in the input audio signal at a first rattle or clatter-causing frequency or frequency band with a first rattle or clatter-causing threshold, and to compare the level of the spectral content in the input audio signal at a second rattle or clatter-causing frequency or frequency band with a second rattle or clatter-causing threshold that differs from the first rattle or clatter threshold. If the level of the spectral content at the first rattle or clatter frequency or frequency band causing the first rattle or clatter noise is greater than the first rattle or clatter noise threshold, the analyzer block 210 can output a first control signal to the processing block 220. If the level of the spectral content at the second rattle or clatter frequency or frequency band causing the second rattle or clatter noise is greater than the second rattle or clatter noise threshold, the analyzer block 210 can output a second control signal (which differs from the first control signal) to the processing block 220.If the level of the spectral content at the first rattle or clatter frequency or frequency band causing rattle or clatter is greater than the first rattle or clatter threshold, and the level of the spectral content at the second rattle or clatter frequency or frequency band causing rattle or clatter is greater than the second rattle or clatter threshold, then the analyzer block 210 can output a third control signal (different from the first and second control signals) to the processing block 220.In other words, the control signal output by the analyzer block 210 to the processing block 220 can indicate the presence or level of a spectral content detected by the analyzer block 210 at the frequencies or frequency bands that cause mechanical rattling or clattering noises in the special host device 100, or may depend on such presence or level. The analyzer block 210 can further be configured to detect a spectral content in the input audio signal at one or more frequencies or frequency bands that could mask mechanical rattle or clatter noises (when converted into an audible output by the audio output converter 110) in the host device 100. In some examples, if a spectral content is detected at such a masking frequency (or frequencies), the analyzer block 210 need not output a control signal to the processing block 220, or it may output a fourth control signal indicating that no processing should be applied to the input audio signal by the processing block 220, thus preventing the processing block 220 from applying the attenuation function.In other examples, analyzer block 210 can be configured to compare the level of such a spectral content with a rattle or clatter masking threshold. If the level of the detected spectral content at one or more masking frequencies is greater than the rattle or clatter masking threshold, analyzer block 210 need not output a control signal to processing block 220, or it can output a fourth control signal indicating that no processing should be applied to the input audio signal by processing block 220, thus preventing processing block 220 from applying the attenuation function. In some examples, if a spectral content is detected at one or more masking frequencies, the analyzer block 210 can output a fifth control signal to the processing block 220, indicating that the processing block 220 should apply a gain function to the input audio signal in order to amplify signal components of the input audio signal at the detected one or more masking frequencies, such that the spectral content of the input audio signal at one or more frequencies or one or more frequency bands that could mask mechanical rattle or clatter noises when converted into an audible output by the audio output converter 110 is amplified, thereby increasing the sound pressure level of such spectral content and enhancing the rattle or clatter noise masking effect in the output of the audio output converter 110. In other examples, the analyzer block 210 is configured to calculate, estimate, or otherwise determine the ratio of a high-frequency content (for example, signal components at frequencies above a predefined high-frequency content threshold) to a total frequency content (that is, a total spectral content of the input audio signal) in the input audio signal and to output a control signal to the processing block 220 to control the processing applied to the input audio signal by the processing block 220, for example, to cause the processing block 220 to apply an attenuation function if the determined ratio falls below a threshold of the ratio of high frequency to total frequency. The high-frequency content in the input audio signal above a certain level could be sufficient to mask mechanical rattle or clatter noises. Therefore, the threshold of the high-frequency to total frequency ratio is determined based on a level of high-frequency content in the input audio signal sufficient to mask mechanical rattle or clatter noises that may occur when the input audio signal is transmitted to the audio output converter 110. As is clear to the average person, the level of high-frequency audio content in the input audio signal sufficient to mask mechanical rattle or clatter noises depends on the configuration and resonance characteristics of the specific host device 100 into which the audio output converter 110 is integrated. Alternatively or additionally, the analyzer block 210 can be configured to calculate, estimate, or otherwise determine a ratio of a low-frequency content (for example, signal components at frequencies below a predefined low-frequency content threshold) to a high-frequency content and output a control signal to the processing block 220 to control the processing applied by the processing block 220 to the input audio signal on the basis of the determined ratio, for example, to cause the processing block 220 to apply an attenuation function if the determined ratio is above a threshold of the low-frequency to high-frequency ratio. A high ratio of low-frequency to high-frequency content may indicate that the input audio signal does not contain sufficient masking content to mask mechanical rattle or clatter that may occur when the input audio signal is transmitted to the audio output converter 110. As noted above, high-frequency content in the input audio signal above a certain level may be sufficient to mask mechanical rattle or clatter, and therefore the threshold of the low-frequency to high-frequency ratio is determined based on the level of high-frequency content in the input audio signal that is sufficient to mask mechanical rattle or clatter in the host device 100 that may occur when the input audio signal is transmitted to the audio output converter 110.As also noted above, the level of high-frequency audio content in the input audio signal, which is sufficient to mask mechanical rattle or clatter noises, depends on the configuration and resonance characteristics of the special host device 100 into which the audio output converter 110 is integrated. If the input audio signal is a digital audio signal, the analyzer block 210 can be designed to analyze the digital audio signal frame by frame and output a control signal (or no control signal) for each frame of the digital audio signal, as described above. The analyzer block 210 can be implemented in different ways. In an example illustrated in Fig. 3, the analyzer block 210 includes a block 212 for a fast Fourier transform (FFT block) (which can be implemented in hardware (for example, in a suitably configured discrete or integrated circuit) or software (for example, in software or firmware running on a digital signal processor, ASIC, general-purpose processor, or the like)), which is configured to perform an FFT on the input audio signal in order to generate a frequency domain representation of the time domain input audio signal received by the analyzer block 210. The analyzer block 210 can be configured to analyze the frequency domain representation of the input audio signal in order to detect signal peaks in the frequency domain representation of the input audio signal at one or more frequencies or frequency bands causing chatter or rattle noises. Upon detection of such signal peaks, the analyzer block can output a control signal to the processing block 220, as described above. Alternatively, the analyzer block 210 can be configured to compare a level (for example, an amplitude) of each detected signal peak with a respective threshold and can output a second or third control signal to the processing block 220 if the one or more detected signal peaks exceed the threshold, as described above. In another alternative example, the analyzer block 210 can be configured to calculate, estimate, or otherwise determine a ratio of the level (for example, the amplitude) of one or more detected high-frequency signal peaks to the level (for example, the amplitude) of one or more detected low-frequency signal peaks, and can output a control signal to the processing block 220 if the determined ratio exceeds a frequency content ratio threshold. The analyzer block 210 can also be configured to analyze the frequency domain representation of the input audio signal in order to detect signal peaks at one or more masking frequencies or masking frequency bands. Upon detection of such signal peaks, the analyzer block does not need to output a control signal to the processing block 220, as described above, so that no processing is applied to the input audio signal by the processing block 220.Alternatively, the analyzer block 210 can be configured to compare the magnitude (for example, amplitude) of the or each detected signal peak at a masking frequency or masking frequency band with a respective threshold, and can output a fifth control signal to the processing block 220 indicating that the processing block 220 should amplify the input audio signal at the one or more detected masking frequencies if the one or more detected signal peaks exceed the one or more thresholds, as described above. In another example, illustrated in Fig. 4, the analyzer block 210 comprises a classifier block 214 or a classifier subsystem (which may be implemented in hardware (for example, in a suitably configured discrete or integrated circuit) or software (for example, in software or firmware running on a digital signal processor, ASIC, general-purpose processor, or the like)) configured to classify the input audio signal into one or more classes according to its spectral content and to output a control signal to the processing block 220 to control the processing applied by the processing block 220 to the input audio signal based on the classification of the input audio signal. For example, classifier block 214 can be configured to classify the input audio signal into one or more of the following classes: pure tone signal; multi-tone signal; single-instrument music; multi-instrument music; speech. If classifier block 214 classifies the input audio signal as a pure tone signal, it outputs an initial control signal to processing block 220 to instruct processing block 220 to apply processing appropriate for a pure tone signal to the input audio signal.If the classifier block 214 classifies the input audio signal into the multi-tone signal class, it similarly outputs a second control signal to the processing block 220 to cause the processing block 220 to apply processing appropriate for a multi-tone signal to the input audio signal, while if the classifier block classifies the input audio signal into the single-instrument music class, the multi-instrument music class, or the speech class, it outputs a third, fourth, or fifth control signal, respectively, to cause the processing block 220 to apply processing appropriate for the class of the input audio signal.If the input audio signal is a digital audio signal, the classifier block 214 can be designed to classify the digital audio signal frame by frame in order to classify each frame of the digital audio signal and output a suitable control signal for each frame of the digital audio signal. In some examples, the classifier block 214 is configured to receive a frequency domain representation of the input audio signal (for example, from an FFT block 212 of the type described above with reference to Fig. 3) and to classify the input audio signal into one or more classes based on the received frequency domain representation. In other examples, the classifier block 214 is configured to receive the input audio signal and to classify the input audio signal into one or more classes based on the input audio signal without transforming it into the frequency domain. Classifier block 214 can be implemented in various ways. In one example, classifier block 214 comprises an artificial neural network or machine learning model that has been trained or otherwise configured to identify features of the input audio signal or a frequency domain representation of the input audio signal, such as frequency peaks (that is, signal level peaks at specific frequencies in the input signal), that are specific or characteristic of each of the one or more classes, and to classify the input audio signal accordingly into the relevant class.The average professional, of course, knows how an artificial neural network or machine learning model must be set up and trained to identify such specific or characteristic features of the input signal (or a frequency domain representation of the input signal) and to classify the input audio signal into one or more classes based on these identified features. Furthermore, it is immediately clear to the average professional that, besides frequency peaks, many other features of the input audio signal (or a frequency domain representation of the input audio signal) could be identified to enable classification of the input audio signal. Additionally or alternatively, the classifier block 214 may be configured to estimate, calculate, or otherwise determine one or more measurements with respect to such features as a peak frequency count (a measurement indicating the number of peak frequencies within one or more specific frequency bands), a difference or ratio of peak frequency counts between different frequency bands, for example, between a high-frequency band (which may be defined as a frequency band above a first threshold frequency) and a low-frequency band (which may be defined as a frequency band below the first threshold frequency or below a second threshold frequency that is lower than the first threshold frequency), and to classify the input audio signal based on the one or more determined measurements. In an alternative example, classifier block 214 can be implemented in hardware (for example, in a suitably configured discrete or integrated circuit) or software (for example, in software or firmware running on a digital signal processor, ASIC, general-purpose processor, or the like) using digital and / or analog signal processing techniques to identify features of the input audio signal (or a frequency-domain representation of the input audio signal) and to classify the input audio signal based on the identified features and / or measurements relating to the identified features. The average person, of course, knows how classifier block 214 can be implemented using such signal processing techniques. The processing block 220 is configured to receive the input audio signal and the control signal output by the analyzer block 210, and to process the input audio signal according to the control signal in order to generate a control signal to be transmitted to an audio output converter 110 of the host device. The processing performed by the processing block 220 reduces mechanical rattle or clatter by selectively applying an attenuation function to the input audio signal to attenuate signal components of the input audio signal at one or more frequencies that cause mechanical rattle or clatter in the host device 100. The processing performed by the processing block can additionally or alternatively apply an amplification function to the input audio signal to amplify signal components of the input audio signal at one or more frequencies that mask mechanical rattle or clatter in the host device 100. If the input audio signal is a digital audio signal, the processing block 220 can be configured to process the digital audio signal frame by frame in order to apply appropriate processing to each frame of the digital audio signal. The attenuation function applied by the processing block 220 is specific to the respective host device 100 into which the audio output converter is integrated and is based on a characteristic acoustic behavior of the respective host device 100. A method for determining an attenuation function (or several attenuation functions) for a specific host device 100 based on the characteristic acoustic behavior of that specific host device 100 is described in detail below. As shown in Fig. 5, the processing block 220 can comprise multiple filters 222-1 to 222-n configured to implement one or more device-specific attenuation functions for the special host device 100 into which the audio output converter 110 is integrated. The multiple filters 222-1 to 222-n can be configured as time-domain filters or as frequency-domain filters. Each of the multiple filters 222-1 - 222-n can be a bandstop filter, configured to block or attenuate signal components at frequencies within a different frequency range (referred to as the filter's stopband) and to allow signal components at frequencies outside the stopband to pass. Alternatively, each of the multiple filters 222-1 - 222-n can be a bandpass filter, configured to allow signal components at frequencies within a different frequency range (referred to as the filter's passband) and to block or attenuate signal components at frequencies outside the passband. The multiple filters 222-1 - 222-n can be narrowband filters, in the sense that the stopband or passband of each of the multiple filters can have a relatively narrow bandwidth (for example, 50 Hz, 100 Hz, 200 Hz). By using multiple narrowband filters, the attenuation applied to the input audio signal can be limited to one or more narrow frequency bands, thereby minimizing the attenuation of the input audio signal in frequency bands for which no attenuation is required. This minimizes or at least reduces the reduction in the sound pressure level of the audio output at the audio output converter 110 (compared to known techniques) and, accordingly, minimizes or at least reduces the volume loss of the audio output.Additionally, the use of multiple narrowband filters can reduce the perception of unwanted coloration of the output audio signal by limiting the attenuation applied to the input audio signal to one or more narrow frequency bands. The multiple filters 222-1 - 222-n can, for example, be arranged in a filter bank. The multiple filters can be implemented in a digital or analog circuit (which may be integrated in one or more integrated circuits), or can be implemented in software running on appropriately configured hardware (for example, firmware running on a digital signal processor IC or IC block, a smart amplifier IC or IC block, or the like). As described above, the control signal output by analyzer block 210 to processing block 220 can depend on analyzer block 210 detecting a spectral content in the input audio signal at one or more frequencies causing chatter or rattle noises, and / or on analyzer block 210 detecting a spectral content in the input audio signal that masks chatter or rattle noises. Additionally or alternatively, the control signal output by analyzer block 210 to processing block 220 can depend on the classification of the input audio signal by classifier block 214, if present. The processing block is designed to apply an attenuation function based on the control signal output by the analyzer block 210. In one example, the processing block 220 is configured to selectively activate or deactivate one or more of the multiple filters 222-1 - 222-n based on the control signal received from the analyzer block 210 for a given input audio signal. For example, if the control signal indicates that a spectral content (or a spectral content at a level above the first rattle or clatter threshold, if applicable) is present in the input audio signal at a single rattle or clatter-causing frequency or frequency range (if, for example, the control signal is a first or second control signal of the type described above), then the processing block 220 may be configured to activate or release the filter of the multiple filters 222-1 - 222-n, which is configured to block or attenuate signal components at the rattle or clatter-causing frequency or frequency range of the detected spectral content of the audio signal. If the control signal received by the analyzer block 210 is a third control signal of the type described above, indicating that a spectral content is present in the input audio signal at both a first rattle- or clatter-causing frequency or frequency range and a second rattle- or clatter-causing frequency or frequency range (at a level above the first and second rattle- or clatter-causing thresholds, if applicable), then the processing block 220 may similarly be configured to activate or release the filters of the multiple filters 222-1 - 222-n, which are configured toTo block or dampen signal components at the first and second frequencies or frequency ranges causing rattling or clattering noises. If no control signal is received from the analyzer block 210, or if the control signal is a fourth control signal of the type described above, indicating that a spectral content at one or more frequencies or one or more frequency bands that could mask mechanical rattle or clatter noises is present in the input audio signal, the processing block 220 may be configured not to activate or release any of the multiple filters 222-1 - 222-n, so that no processing is applied to the input audio signal by the processing block. If the control signal received by analyzer block 210 is a fifth control signal of the type described above, indicating that the input audio signal contains a spectral content to be amplified at one or more masking frequencies or masking frequency ranges, then processing block 220 may be configured to apply a gain function to the input audio signal. The gain function may be applied by increasing the gain of those filters of the multiple filters 222-1 - 222-n, which are configured to allow signal components at the masking frequencies or masking frequency ranges to pass, to a value greater than one, so that the spectral content of the input audio signal at the masking frequencies is amplified by processing block 220. In another example, illustrated in Fig. 6, the processing block can comprise one or more dynamically reconfigurable filters 224 implemented in a digital or analog circuit (which may be integrated in one or more integrated circuits), or implemented in software running on suitably configured hardware (for example, firmware running on a digital signal processor IC or IC block, a smart amplifier IC or IC block, or the like). Alternatively, each dynamically reconfigurable filter 224 can be configured as a time-domain filter or as a frequency-domain filter. A transfer function of the (or any) dynamically reconfigurable filter 224 can be dynamically reconfigurable, so that the dynamically reconfigurable filter 224 can implement several different attenuation functions. The transfer function of the dynamically reconfigurable filter 224 is controlled or selected by the processing block 220 based on the control signal received by the processing block 220 from the analyzer block 210. For example, if the control signal indicates that a spectral content (or a spectral content at a level above the first rattle or clatter threshold, if applicable) is present at a single rattle or clatter-causing frequency or frequency range in the input audio signal or in an instantaneous frame of the input audio signal (if, for example, the control signal is a first or second control signal of the type described above), then the processing block 220 may be configured to cause the dynamically reconfigurable filter 224 to use a first transfer function in which the dynamically reconfigurable filter 224 is configured as a bandstop filter.to block or attenuate signal components at the frequency or frequency range of the detected spectral content of the audio signal that causes rattling or clattering noises. If the control signal received by the analyzer block 210 is a third control signal of the type described above, indicating that a spectral content is present in the input audio signal or in a momentary frame of the input audio signal at both a first rattle- or clatter-causing frequency or frequency range and a second rattle- or clatter-causing frequency or frequency range (at a level above the first and second rattle- or clatter-causing thresholds, if applicable), then the processing block 220 may similarly be configured to cause the dynamically reconfigurable filter 224 to use a second transfer function to configure the dynamically reconfigurable filter 224 toTo block or dampen signal components at the first and second frequencies or frequency ranges causing rattling or clattering noises. If no control signal is received from the analyzer block 210, or if the control signal is a fourth control signal of the type described above, indicating that a spectral content at one or more frequencies or frequency bands that could mask mechanical rattle or clatter noises is present in the input audio signal, the processing block 220 may be configured to cause the dynamically reconfigurable filter 224 to use a third transfer function in which the dynamically reconfigurable filter 224 acts as an all-pass filter with a gain of one, so that no processing is applied to the input audio signal by the processing block 220.If the control signal received by the analyzer block 210 is a fifth control signal of the type described above, indicating that the input audio signal contains a spectral content to be amplified at one or more masking frequencies or masking frequency ranges, then the processing block 220 may be configured to apply a gain function to the input audio signal by, for example, causing the dynamically reconfigurable filter 224 to use a fourth transfer function in which the dynamically reconfigurable filter 224 acts as a multiband bandpass filter with a gain greater than one in the passbands, such that the dynamically reconfigurable filter 224 is configured to pass signal components at the masking frequencies or masking frequency ranges.so that the spectral content of the input audio signal at the masking frequencies is amplified by processing block 220. In another example (illustrated in Fig. 7), in which the analyzer block 210 includes a classifier block 214, the processing block 220 can be configured to selectively apply one or more of several masks 226-1 - 226-n to the input audio signal based on the classification of the input audio signal by the classifier block 214. Each of the multiple masks 224-1 - 224-n is tailored to a specific class of input audio signals and is configured to implement an attenuation function to attenuate any spectral content in the input audio signal that causes rattling or clattering noises in a manner that optimizes or enhances a property or characteristic such as fidelity or clarity of the audio output by the audio output converter 110, as perceived by a listener. This means that if, for example, the classifier block 214 classifies the input audio signal as belonging to the pure tone signal class, the processing block 220 can select a first mask 226-1 of the several masks 226-1 - 226-n to apply to the audio signal in order to dampen any spectral content in the input audio signal that causes rattling or clattering noises, in order to optimize or at least improve the (perceived by the listener) fidelity of the audio output. If the classifier block 214 classifies the input audio signal as belonging to the multi-tone signal class, the single-instrument music class, or the multi-instrument music class, the processing block 220 can similarly select one of the several masks 226-1 - 226-n that is matched to the class in question in order to apply it to the input audio signal in order to attenuate any spectral content in the input audio signal that causes rattling or clattering noises, in order to optimize or at least improve the (perceived by the listener) fidelity of the audio output. If, however, the classifier block 214 classifies the input audio signal as belonging to the speech class, the processing block 220 can select one of the several masks 226-1 - 226-n that is matched to the speech class in order to apply it to the input audio signal in order to dampen any spectral content in the input audio signal that causes rattling or clattering noises, in order to optimize or at least improve the intelligibility of the audio output (as perceived by the listener). The multiple masks 226-1 - 226-n can be implemented by multiple filters 222-1 - 222-n of the type described above with reference to Fig. 5, or can be implemented by one or more dynamically reconfigurable filters 224 of the type described above with reference to Fig. 6. Fig. 8 is a diagram illustrating the principle of reducing rattling or clattering noises in an audio system of a host device by means of a control loop, according to one aspect of the present disclosure. Fig. 8 has some similarities with Fig. 1, so that identical features in Fig. 1 and Fig. 8 are identified by the same reference numerals. As shown in Fig. 8, an input transducer 840 of a host device 100, such as a laptop, tablet, or all-in-one desktop PC, transmits a feedback signal to a subsystem 830 to reduce rattling or clattering noises. The input transducer 840 can be a microphone, an accelerometer, or any other suitable transducer of the host device 100. The rattle or clatter reduction subsystem 830 is configured to receive the feedback signal from the input converter 840 while audio is being output by the audio output converter 110, and to detect distortions caused by mechanical rattle or clatter noises based on the feedback signal. The rattle or clatter reduction subsystem 830 is further configured to apply countermeasures to reduce the distortions, for example, by applying an attenuation function to the input audio signal received by the rattle or clatter reduction subsystem and / or by amplifying signal components of the input audio signal at masking frequencies, as described above with reference to Figures 1-7. The rattle or clatter reduction subsystem 830 can be configured to detect distortion based on the feedback signal, for example, by comparing the feedback signal received by the input converter 840 with the audio signal received by the audio system 120. The rattle or clatter reduction subsystem 830 can also be configured to monitor the sound pressure level (SPL) of the audio output through the audio output converter 110 based on the feedback signal transmitted by the input converter 840, and can apply countermeasures to reduce distortion if the SPL falls below a specified threshold. In an alternative example, the baseband content of the audio output by the audio output converter 110 and associated harmonics by the subsystem 830 are monitored to reduce chatter or rattle noise (based on the feedback signal transmitted by the input converter 840) in order to detect distortion. In some examples, the 130 / 830 subsystem for rattle or clatter reduction may be configured to apply the attenuation function according to an attack / release function that gradually increases the degree of attenuation applied to the input audio signal by the 130 / 830 subsystem for rattle or clatter reduction. In such examples, the analyzer block 210 (or another decision block) may analyze the spectral content of the input audio signal as described above to identify any signal components of the input audio signal that would result in mechanical rattle or clatter if transmitted to the audio output converter 110 without the application of an attenuation function.If such signal components are identified, the processing block 220 can progressively apply the attenuation function over a period of time to gradually increase the attenuation applied to the input audio signal from a minimum attenuation level to a maximum attenuation level, such that the maximum attenuation level is applied to signal components of the input audio signal that may cause mechanical rattling or clattering noises if transmitted to the audio output converter 110 without attenuation. As explained above, the processing block 220 can be designed to apply an attenuation function only if one or more predefined conditions are met – for example, if a spectral content causing rattle or clattering noises (above a threshold) is detected in the input audio signal, if a level of masking content in the input audio signal is below a threshold, if a ratio of high-frequency content to total frequency content is below a threshold of the ratio of high frequency to total frequency, or if a ratio of the level of low-frequency content to high-frequency content in the audio signal is above a threshold of the ratio of low frequency to high frequency.In some examples, the ratio of high-frequency content to total frequency content in the input audio signal and / or the ratio of low-frequency content to high-frequency content in the input audio signal can be used to determine the degree of attenuation applied by the attenuation function, for example, a percentage of the maximum attenuation applied by Processing Block 220. For example, a higher ratio of low-frequency content to high-frequency content allows for a higher percentage of the maximum attenuation to be applied, while lower ratios allow for a lower percentage. In some examples, Processing Block 220 can perform a "fast limit" to immediately apply the maximum attenuation to the input audio signal if the degree of attenuation is greater than 0. As previously noted, processing block 220 can be configured to process a digital audio signal frame by frame, applying appropriate processing to each frame. Thus, the attenuation function applied to one frame of the digital audio signal can differ from the attenuation function applied to a previous or subsequent frame. Processing block 220 can be configured to execute a smoothing function to smooth the transition between different attenuation functions applied to adjacent frames of the input audio signal, thereby reducing the risk of audible artifacts, such as clicks and pops, being introduced into the audio output.For example, processing block 220 may be configured to perform linear interpolation to transition from a first attenuation function applied to a frame of the input audio signal to a second attenuation function applied to a subsequent frame of the input audio signal, or to produce exponential decay in a transition between the first and second attenuation functions. The processing block 220 can be configured to apply the attenuation and / or gain function in the frequency domain or the time domain. The processing block can therefore be configured to convert the time-domain input audio signal into a frequency-domain signal (for example, by performing an FFT operation on the input audio signal) and apply the attenuation and / or gain function to the frequency-domain signal to generate a processed frequency-domain signal. This processed frequency-domain signal can be transformed back into the time domain (for example, by performing an inverse FFT operation on the processed frequency-domain signal) to generate a time-domain drive signal that can be transmitted to the audio output converter 110. In some examples, processing block 220 can be configured to selectively apply the attenuation and / or gain function based on one or more features, characteristics, or classifications of the input audio signal in the frequency or time domain. For example, if minimizing latency in the audio output is important, processing block 220 can be configured to apply the attenuation and / or gain function in the time domain, while processing block 220 can be configured to apply the attenuation and / or gain function in the frequency domain if maximum audio fidelity is a priority. In examples where analyzer block 210 includes classifier block 214, processing block 220 can be configured to selectively apply the attenuation function and / or the gain function based on the time-domain or frequency-domain classification of the input audio signal. For example, if the input audio signal is classified by classifier block 214 as belonging to the speech class, where low latency may be more important than high audio fidelity, processing block 220 can apply the attenuation function and / or the gain function in the time domain.If, however, the audio signal is classified by the classifier block 214 as belonging to the single-instrument music class or the multi-instrument music class, where audio fidelity may be more important than low latency, the processing block 220 can apply the attenuation function and / or the gain function in the frequency domain. In examples where analyzer block 210 does not include a classifier block, processing block 220 can be configured to selectively apply the attenuation function and / or the gain function based on features of the input audio signal identified by analyzer block 210 that may indicate the nature of the content represented by the audio signal. For example, if the features of the input audio signal indicate that the input audio signal represents speech, where low latency may be more important than high audio fidelity, processing block 220 can apply the attenuation function and / or the gain function in the time domain.However, if the characteristics of the input audio signal indicate that it represents single-instrument or multi-instrument music, where audio fidelity may be more important than low latency, then processing block 220 can apply the attenuation and / or gain functions in the frequency domain. The average professional, of course, knows how to detect features of an audio signal that indicate the type of audio content represented by the signal. As noted above, the frequency or frequencies of a spectral component of the input audio signal that can cause mechanical rattling or clattering noises in the host device 100 are specific to that particular host device 100 insofar as they depend on its characteristics and / or configuration. Therefore, to configure subsystem 130 for reducing rattling or clattering noises in a specific host device 100, it is necessary to determine or evaluate the characteristic behavior of the host device 100 in order to identify the frequency or frequencies of a spectral component of the input audio signal that can cause mechanical rattling or clattering noises in the host device 100.Once the characteristic behavior of the host device 100 has been determined or evaluated, the analyzer block 210 can be configured with appropriate frequency or frequency band information and thresholds to enable it to identify components of the input audio signal that cause chatter or rattle noise; the classifier block 214 (if present) can be appropriately configured (for example, equipped with suitable weights or the like); and the filter(s) 222-2 - 222-n, 224 and / or the masks 226-1 - 226-n of the processing block 220 can be appropriately configured (for example, equipped with appropriate filter coefficients or the like). Fig. 9 is a flowchart showing the steps in a method 900 for determining or evaluating the characteristic acoustic behavior of a host device 100. The method 900 can be performed, for example, during a tuning stage, which may be part of an assembly or initial setup process of the host device 100. In the first step of the procedure, 902, a stimulus signal is output by the audio system 120. In this step, no damping or amplification function is applied by subsystem 130, 830 to reduce rattling or clattering noises, so that the stimulus signal is transmitted as a drive signal to the audio output converter 110. The stimulus signal can, for example, comprise a single-tone signal of variable frequency and amplitude, or a multi-tone signal in which the frequency and amplitude of each individual tone are variable. The stimulus signal can be configured to simulate an audio signal that would be output by the audio system 120 when using the host device 100. In step 904, one or more properties of the stimulus signal are adjusted while the host device 100 is monitored for mechanical rattle or clattering noises or other mechanical resonance effects. For example, the frequency of the stimulus signal (or one or more individual tones of the stimulus signal in the case of a multi-tone stimulus signal) can be sweeped over a predefined frequency range (for example, 20 Hz - 20 kHz) while the amplitude of the stimulus signal (or its individual tones) is kept constant and the host device 100 is monitored for mechanical rattle or clattering noises or other mechanical resonance effects.Alternatively, the amplitude of the stimulus signal can be adjusted over a predefined range from a minimum amplitude to a maximum amplitude, while the frequency of the stimulus signal (or its individual tones) is kept constant and while the host device is monitored for mechanical rattle or clatter noises or other mechanical resonance effects. The frequency (or frequencies) and amplitudes of the stimulus signal at which mechanical rattle or clatter noise or other mechanical resonance effect is detected are recorded (step 906) to generate a distortion frequency profile for the host device 100 (step 908), which can then be used (in step 910) to configure the rattle or clatter reduction subsystem 130, 830 with suitable thresholds, frequencies, weights, masks, etc., as described above, to attenuate rattle or clatter-causing signal components of the input audio signal fed into the rattle or clatter reduction subsystem and / or to amplify rattle or clatter masking components of the input audio signal to generate the drive signal for driving the audio output converter. The host device 100 can be monitored for mechanical rattle or clattering noises or other mechanical resonance effects using an input transducer such as a microphone, accelerometer, or the like. Alternatively, an external transducer such as a microphone, accelerometer, or the like from a distortion monitoring system can be used outside the host device 100 to monitor the host device 100 for mechanical rattle or clattering noises or other mechanical resonance effects. In an alternative example of Procedure 900, the stimulus signal may comprise several tones, which may have a fixed amplitude and may be spaced apart in frequency. Applying such a stimulus signal may enable faster identification of frequencies that give rise to mechanical rattling or clattering noises, or other mechanical resonance effects, in the host device 100. When such a stimulus signal is applied, step 906 of the procedure may be unnecessary. The host device 100 can have multiple audio output converters. Steps 902–908 of the method 900 described above with reference to Fig. 9 can be performed separately for each of the multiple audio output converters to generate multiple distortion frequency profiles—one for each of the multiple audio output converters. The chatter or rattle reduction subsystem 130, 830 can be configured, based on the multiple distortion frequency profiles as described above, with suitable thresholds, frequencies, weights, masks, etc., to attenuate chatter or rattle-causing signal components of the input audio signal to the chatter or rattle reduction subsystem and / or to amplify chatter or rattle-masking components of the input audio signal to generate drive signals for driving each of the multiple audio output converters. In addition to performing the procedure 900 during a tuning stage of an assembly or initial setup process of the host device 100, the procedure 900 can also be performed periodically or in response to a trigger condition after the assembly or setup of the host device 100 in order to update the rattle or clatter reduction subsystem 130, 830 with updated thresholds, frequencies, weights, masks, etc., to account for aging of the host device 100, the one or more audio output transducers 110, and the rattle or clatter reduction subsystem 130, 830, and / or changes in the physical environment in which the host device 100 is used.When carrying out procedure 900 for such an update, an input converter, such as the input converter 840, is used to monitor one or more audio output signals of one or more audio output converters 110. As is known to the average person skilled in the art, the problem of mechanical rattle or clatter noises or resonance is not unique or specific to computer devices. Mechanical rattle or clatter noises, or other undesirable effects caused by mechanical resonance at audio frequencies, can also occur in other applications where an audio output converter is mechanically coupled to part of a host device, for example, in automotive audio systems where loudspeakers are mechanically mounted to or otherwise coupled to interior trim panels. The system and method described herein are applicable to such other applications. Accordingly, the present disclosure extends to a system for reducing mechanical rattle or clatter noises in a more general sense and to a system for reducing resonance at audio frequencies. The system described above with reference to the accompanying drawings can be integrated into a host device, such as a laptop, notebook, netbook or tablet computer, an all-in-one computer, a gaming device, such as a game console or a game console controller, a virtual reality (VR) device or augmented reality (AR) device, a mobile phone, a portable audio player or other portable device, or can be integrated into an accessory device for use with a laptop, notebook, netbook or tablet computer, a gaming device, a VR or AR device, a mobile phone, a portable audio player or other portable device, a vehicle such as a car, van, truck or the like. A person skilled in the art will recognize that some aspects of the device and method described above can be embodied as processor control code, for example, on a non-volatile storage medium such as a floppy disk, CD-ROM, or DVD-ROM, in programmed memory such as read-only memory (firmware), or on a data carrier such as an optical or electrical signal carrier. For many applications, embodiments of the invention are implemented in a DSP (digital signal processor), an ASIC (application-specific integrated circuit), or an FPGA (field-programmable gate array). Thus, the code can comprise conventional program code or microcode, or, for example, code for setting up or controlling an ASIC or FPGA. The code can also include code for dynamically configuring reconfigurable devices, such as reprogrammable logic gate arrays.Similarly, the code can include code for a hardware description language such as Verilog™ or VHDL (Very high-speed integrated circuit Hardware Description Language). As is obvious to those skilled in the art, the code can be distributed among several coupled components that communicate with each other. Optionally, the embodiments can also be implemented using code that runs on a field-programmable analog array or a similar device to configure analog hardware. It should be noted that, for the purposes of this text, the term "module" refers to a functional unit or block that can be implemented at least partially by dedicated hardware components, such as task-specific circuits, and / or at least partially by one or more software processors or suitable code running on a suitable general-purpose processor or the like. A module may itself comprise other modules or functional units. A module can be formed by multiple components or submodules that need not be located in the same place and that could be deployed on different integrated circuits and / or run on different processors. When two or more elements are described as being “coupled”, this term, in the context of this text, means that these two or more elements are in electronic or mechanical communication, regardless of whether they are connected indirectly or directly, or with or without intervening elements. This disclosure includes all changes, replacements, variations, alterations, and modifications of the exemplary embodiments contained in the present text that a person skilled in the art would understand. Likewise, the appended claims include all changes, replacements, variations, alterations, and modifications of the exemplary embodiments contained in the present text that a person skilled in the art would understand. Furthermore, the reference in the appended claims to a device or system, or a component of a device or system, that is suitable, designed, capable, configured, able, operable, or arranged to perform a particular function, includes that device, system, or component, regardless of whether it is a device or system or a component of a device or system.Whether or not that particular function is activated, switched on, or unlocked is irrelevant, as long as that device, system, or component is suitable, designed, capable, configured, enabled, operable, or set up in such a manner. Accordingly, modifications, additions, or omissions may be made to the systems, devices, and methods described herein without altering the scope of protection afforded by the disclosure. For example, the components of the systems and devices may be integrated or separate. Furthermore, the operations of the systems and devices disclosed herein may be performed by more, fewer, or different components, and the described methods may include more, fewer, or different steps. Additionally, the steps may be performed in any suitable sequence.For the purposes of this document, “each” refers to each element of a set or each element of a subset of a set. Although exemplary embodiments are illustrated in the figures and described below, the principles of this disclosure can be implemented using any number of techniques, whether currently known or not. This disclosure should in no way be limited to the exemplary embodiments and techniques illustrated in the drawings and described above. Unless explicitly stated otherwise, objects illustrated in the drawings are not necessarily drawn to scale. All examples and conditional formulations cited in this text serve the purpose of conveying the teaching, in order to assist the reader in understanding the disclosure and the concepts to which the inventor contributes technical progress, and are to be interpreted as not constituting any limitation of such specifically cited examples and conditions. Although embodiments of the present disclosure have been described in detail, it is understood that various changes, substitutions, and modifications may be made to them without departing from the essence and scope of the invention. Although specific advantages have been listed above, different embodiments may include some, none, or all of the listed advantages. Furthermore, after studying the figures mentioned above and the preceding descriptions, the average person skilled in the art will readily recognize additional technical benefits. It should be noted that the embodiments mentioned above illustrate, not limit, the invention, and that a person skilled in the art will be able to design many alternative embodiments without deviating from the scope of protection of the appended claims. The word "comprise" does not exclude the presence of elements or steps not listed in a claim. "A" does not exclude the plurality; and a single feature or other unit may perform the functions of various units mentioned in the claims. Reference numerals or identifiers in the claims are not to be interpreted as limiting the scope of protection of the claims.

Claims

A computer comprising a system for reducing mechanical rattle or clatter noises resulting from a mechanical coupling of an audio output converter to a part of the computer device, wherein the system comprises: a processing subsystem configured to receive an input audio signal and to output a drive signal to drive the audio output converter in order to generate a converter output, wherein the processing subsystem is configured to selectively apply an attenuation function to the input audio signal in order to attenuate a signal component of the input audio signal at a frequency that causes mechanical rattle or clatter noises in the computer;and an analyzer subsystem configured to receive the input audio signal and output a control signal to the processing subsystem to control the application of the attenuation function to the input audio signal by the processing subsystem based on a spectral content of the received input audio signal; wherein the attenuation function is based on a characteristic acoustic behavior of the computer. Computer according to claim 1, wherein the processing subsystem is further configured to selectively apply an amplification function to the input audio signal in order to amplify a signal component of the input audio signal at a frequency that masks an effect of mechanical rattling or clattering noises in the computer device. Computer according to claim 1 or claim 2, wherein the analyzer subsystem comprises a classifier configured to classify the input audio signal into one or more classes based on the spectral content of the input audio signal and to output a control signal to the processing subsystem to control the application of the attenuation function to the input audio signal by the processing subsystem based on the classification of the input audio signal. Computer according to claim 3, wherein the classifier comprises a neural network or a machine learning model trained to identify features of the input audio signal that are characteristic of each of the one or more classes and to classify the input audio signal on the basis of the identified features of the input audio signal. Computer according to claim 3, wherein the classifier comprises a neural network or a machine learning model trained to identify features of the input audio signal that are characteristic of each of the one or more classes, wherein the classifier is configured to determine a measurement with respect to identified features of the input audio signal and to classify the input audio signal on the basis of the measurement. Computer according to one of the preceding claims, wherein the analyzer subsystem is configured to output the control signal in response to the detection of a spectral content in the input audio signal at a level above a rattle or clatter noise threshold at a frequency that could lead to mechanical rattle or clatter noises in the computer device. Computer according to one of the preceding claims, wherein the analyzer subsystem is configured to determine a first ratio of high-frequency content to low-frequency content of the input audio signal and / or a second ratio of low-frequency content to high-frequency content of the input audio signal and to output a control signal to the processing block to control the application of the attenuation function based on the determined first and / or second ratio. Computer according to any of the preceding claims, wherein the analyzer subsystem is configured to perform a Fast Fourier Transform (FFT) of the input audio signal in order to generate a frequency domain representation of the input audio signal received by the analyzer block. Computer according to claim 8, wherein the analyzer subsystem is configured to output the control signal in response to the detection of a signal peak in the frequency domain representation of the input audio signal at a frequency that could lead to mechanical rattling or clattering noises in the computer device. Computer according to claim 9, wherein the analyzer subsystem is configured to output the control signal in response to the detection of a signal peak in the frequency domain representation of the input audio signal at a level above a rattle or clatter noise threshold at a frequency that could lead to mechanical rattle or clatter noises in the computer device. Computer according to claim 8, wherein the analyzer subsystem is configured to determine a ratio of a level of a detected high-frequency signal peak in the frequency domain representation of the input audio signal to a level of a detected low-frequency signal peak in the frequency domain representation and to output the control signal if the determined ratio exceeds a frequency content ratio threshold. Computer according to any of the preceding claims, wherein the analyzer subsystem is configured to prevent the processing subsystem from applying the damping function in response to the detection of a spectral content in the input audio signal at a frequency that could mask mechanical rattle or clatter noises in the computer. Computer according to claim 12, wherein the analyzer subsystem is configured to prevent the processing subsystem from applying the damping function in response to the detection of a spectral content in the input audio signal at a level above a rattle or clatter masking threshold at a frequency that could mask mechanical rattle or clatter noises in the computer. Computer according to claim 2, wherein the analyzer subsystem is configured to output a control signal to cause the processing subsystem to apply the amplification function in response to the detection of a spectral content in the input audio signal at a frequency that could mask mechanical rattle or clatter noises in the computer. Computer according to any of the preceding claims, wherein the input audio signal is a digital signal comprising multiple frames, wherein the analyzer subsystem is configured to output a control signal to the processing subsystem for each frame of the input audio signal based on the spectral content of the frame, in order to control the application of the attenuation function or to prevent the processing subsystem from applying the attenuation function. Computer according to one of the preceding claims, wherein the processing subsystem comprises one or more filters configured to implement the damping function. Computer according to claim 16, wherein the filter or each filter comprises a narrowband filter. Computer according to claim 16, wherein the or each filter comprises a dynamically reconfigurable filter having a controllable transfer function, wherein the processing subsystem is configured to control the transfer function of the or each dynamically reconfigurable filter on the basis of a control signal received from the analyzer subsystem. Computer according to one of claims 16 - 18, wherein the filter or each filter comprises a time domain filter or a frequency domain filter. Computer according to claim 3, wherein the processing subsystem is configured to selectively apply one or more masks to the input audio signal based on the classification of the input audio signal by the classifier, wherein the or each mask is configured to implement an attenuation function to attenuate the spectral content in the input audio signal that causes rattling or clattering noises in order to optimize or improve a property of the converter output signal. Computer according to claim 20, wherein the processing system is configured to apply a first mask in response to a classification of the audio input signal as music in order to optimize or improve the fidelity of the converter output, and to apply a second mask in response to a classification of the audio input signal as speech in order to optimize or improve the intelligibility of the converter output. Computer according to any of the preceding claims, wherein the computer comprises an input converter, and wherein the processing subsystem is configured to: receive a feedback signal from the input converter; detect distortion in the converter output based on the feedback signal; and in response to the detection of distortion in the converter output, apply the attenuation function and / or a gain function to the audio input signal. Computer according to claim 22, wherein the processing subsystem is configured to monitor one or more of a sound pressure level of the converter output and a baseband content and associated harmonics of the converter output based on the feedback signal in order to detect distortions in the converter output. Computer according to one of the preceding claims, wherein the processing subsystem is configured to apply the damping function according to an attack / release function. Computer according to claim 24, wherein the processing subsystem is configured to progressively apply the damping function to the audio input signal over a period of time from a minimum damping level to a maximum damping level such that the maximum damping level is applied to a spectral content of the audio input signal at a frequency that could lead to mechanical rattling or clattering noises in the computer device. Computer according to claim 3, wherein the processing subsystem is configured to selectively apply the damping function in the time domain or in the frequency domain based on the classification of the input signal by the classifier. Computer according to claim 26, wherein the processing subsystem is configured to apply the attenuation function in the time domain in response to a classification of the audio input signal as speech and to apply the attenuation function in the frequency domain in response to a classification of the audio input signal as music. Computer according to claim 1, wherein the processing subsystem is configured to selectively apply the damping function in the time domain or in the frequency domain based on the identification of features of the input audio signal by the analyzer subsystem. Computer according to claim 28, wherein the processing subsystem is configured to apply the attenuation function in the time domain in response to the identification of features of the audio input signal indicating that the audio input signal represents speech, and to apply the attenuation function in the frequency domain in response to the identification of features of the audio input signal indicating that the audio input signal represents music. Computer according to any of the preceding claims, wherein the computer is a laptop computer, a tablet computer or an all-in-one desktop computer. A method for evaluating the characteristic acoustic behavior of a computer comprising an audio output converter, wherein the method comprises: supplying a stimulus signal to the audio output converter; monitoring the computer to detect a mechanical resonance effect in the computer; and generating a distortion frequency profile for the computer based on a frequency and amplitude of the stimulus signal for which a mechanical resonance effect was detected in the computer device. Method according to claim 31, wherein the monitoring of the computer device for detecting a mechanical resonance effect is carried out using an input converter of the computer. Method according to claim 31, wherein the stimulus signal comprises several tones that are spaced apart in their frequency. System for reducing mechanical rattling or clattering noises in a computer caused by mechanical coupling of an audio output converter to a part of the computer, wherein the system comprises: a processing subsystem configured to receive an input audio signal and output a drive signal to drive the audio output converter to generate a converter output, wherein the processing subsystem is configured to selectively apply an attenuation function to the input audio signal to attenuate a signal component of the input audio signal at a frequency that causes mechanical rattling or clattering noises in the computer, wherein the attenuation function is based on a characteristic acoustic behavior of the computer. System for reducing mechanical rattling or clattering noises in a computer caused by mechanical coupling of an audio transducer to a part of the computer, the system comprising: a classifier subsystem configured to classify the audio input signal into one or more of several classes; and a processing block configured to selectively apply an attenuation function to the input signal in order to attenuate a signal component of the audio input signal according to the classification of the audio input signal. A system for reducing mechanical rattling or clattering noises in a computer caused by a mechanical coupling of an audio transducer to a part of the computer, the system comprising: a classifier subsystem configured to classify the audio input signal into one or more of several classes; and a processing block configured to apply an attenuation function from several attenuation functions to the input signal in order to attenuate a signal component of the audio input signal, the processing block being configured to select the attenuation function based on the classification of the audio input signal. A system for reducing mechanical rattling or clattering noises in a computer caused by a mechanical coupling of an audio transducer to a part of the computer, the system comprising: a classifier subsystem configured to classify the audio input signal into one or more of several classes; and a processing block configured to selectively apply an attenuation function to the input signal in order to attenuate a signal component of the audio input signal, the processing block being configured to apply either a frequency domain attenuation function or a time domain attenuation function according to the classification of the audio input signal. System for reducing mechanical resonance in a host device caused by mechanical coupling of an audio output converter to a part of the computer, wherein the system comprises: a processing subsystem configured to receive an input audio signal and output a drive signal to drive the audio output converter to generate a converter output, wherein the processing subsystem is configured to selectively apply an attenuation function to the input audio signal to attenuate a signal component of the input audio signal at a frequency that causes mechanical resonance in the host device. Integrated circuit implementing the system according to one of claims 34-38. Integrated circuit according to claim 39, wherein the integrated circuit comprises an integrated circuit designed as an intelligent amplifier. Host device comprising the system according to any one of claims 34-38. Host device according to claim 41, wherein the host device comprises a laptop, notebook, netbook or tablet computer, an all-in-one computer, a gaming device, a game console, a controller for a game console, a virtual reality device (VR device) or augmented reality device (AR device), a mobile phone, a portable audio player, a portable device, an accessory device for use with a laptop, notebook, netbook or tablet computer, a gaming device, a game console, a VR or AR device, a mobile phone, a portable audio player or any other portable device, or a vehicle.

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