Abstract: A hearing aid includes a microphone for converting sound into an audio input signal, a hearing loss processor configured for processing the audio input signal or a signal derived from the audio input signal in accordance with a hearing loss of a user of the hearing aid, a synthesizer configured for generation of a synthesized signal based at least on a sound model and the audio input signal, the synthesizer comprising a noise generator configured for excitation of the sound model for generation of the synthesized signal including synthesized vowels, and a receiver for generating an output sound signal based at least on the synthesized signal.

Abstract: The present invention relates to a new type of hearing aid with a housing that is adapted for positioning in the ear canal of a user and attached to an elongate member that is adapted for positioning in the pinna outside the ear canal of the user. The elongate member is adapted for removable interconnection with the hearing aid the housing of which is adapted for positioning in the ear canal of a user and accommodates a signal processor for processing an audio signal into an audio signal compensating a hearing loss and a receiver that is connected to an output of the signal processor for converting the processed compensated audio signal into a sound signal.

Abstract: A device and methods are provided for a hearing device. In one embodiment, a hearing device includes a microphone to receive sound, an interactive tip and actuator. The actuator can include an actuator element and preload force element to place the interactive tip in contact with a portion of an ear. The hearing device includes circuitry coupled to the microphone and actuator, the circuitry configured to process sound received by the microphone and drive the actuator based on processed sound, wherein the actuator drives the interactive tip relative to a portion of the ear based on one or more signals received from the circuitry.

Abstract: The invention relates to a method for a hearing aid wearer to actively operate a hearing aid. A signal processing section of the hearing aid has a demixing module for separating audio signals and a postprocessor module which sets up a hold mode of operation for the hearing aid. An audio signal, which is preferred by the hearing aid wearer, from an ambient sound, is tracked and selected by virtue of the hearing aid wearer transmitting to the hearing aid a command which sets up the hold mode of operation in the signal processing section of the hearing aid for a certain period. The signal processing section tracks the preferred audio signal and selectively takes account of it in an output sound from the hearing aid such that it is audibly highlighted for the hearing aid wearer in comparison with another audio signal and is thereby perceived better.

Abstract: In one embodiment, an apparatus comprises an adaptive filter, a timing recovery unit, and a reverse interpolation filter. The adaptive filter has adaptive filter coefficients that are adjusted based on a first error signal at a first sample rate and filters a first signal at the first sample rate to obtain a second signal at the first sample rate. The timing recovery unit interpolates the second signal at the first sample rate to obtain a third signal at a second sample rate; and estimates a partial response signal at the second sample rate corresponding to the third signal. The a reverse interpolation filter interpolates a second error signal at the first sample rate, which is a difference between the third signal and the partial response signal, to obtain the first error signal at the first sample rate for feeding back to the adaptive filter.

Abstract: The invention relates to a hearing instrument for processing an input sound to an output sound according to a user's needs. The invention further relates to a method of operating a hearing instrument and to use of a hearing instrument. The object of the present invention is to provide an alternative scheme for handling acoustic feedback in a hearing instrument.

Abstract: A method for determining a maximum gain is disclosed that is applicable in a forward signal path starting at a microphone (1) and ending at a receiver (11) of a hearing device, the maximum gain being a gain value at which just no feedback occurs. The method comprising the steps of estimating a estimated feedback transfer function (F?) characterizing a feedback signal path (15) starting at a receiver (11) and ending at a microphone (1) of the hearing device, while the hearing device is inserted into an ear of a hearing device user, and adapting the estimated feedback transfer function (F?) as a result of a changing feedback signal path (15) by applying an adaptive algorithm. The invention is characterized by determining the maximum gain from the estimated feedback transfer function (F?), in particular by coefficients of the estimated feedback transfer function.

Abstract: The circuit complexity or the filter order, respectively, of an analysis/synthesis filter bank system especially for hearing aids is to be reduced. For this reason, the stop-band attenuation of at least one of the transfer functions of the analysis filter bank is composed of a separately configurable, frequency-independent analysis basic attenuation component and a separately configurable frequency-dependent analysis attenuation component. Furthermore, the stop-band attenuation of at least one of the transfer functions of the synthesis filter bank is composed of a separately configurable, frequency-independent synthesis basic attenuation component, a separately configurable, frequency-dependent first synthesis attenuation component and a separately configurable, frequency-dependent second synthesis attenuation component which is also dependent on the manipulation of the sub-band signals.

Abstract: To enable hearing apparatus feedback to be reliably detected, it is provided that the hearing apparatus has an analyzer for analyzing the resonant behavior of the overall system as a function of a modification of the signal processing device and for determining from the analysis result a feedback variable constituting a measure of the feedback. On the basis of the feedback variable, an adaptive compensation filter, for example, can then be step-size-controlled to compensate the feedback.

Abstract: A method for signal processing for a hearing aid aims to better match signal processing for a hearing aid and in particular a hearing device to a situation and includes processing an input signal in accordance with a first processing algorithm to form a first intermediate signal and processing the input signal in accordance with a second processing algorithm to form a second intermediate signal in parallel with the processing of the input signal in accordance with the first processing algorithm. The input signal is classified by a classifier. Finally, an output signal with a constant mixture ratio is formed both from the first and from the second intermediate signals, taking into account the result of the classification. This allows the advantages of a plurality of algorithms to be used at the same time. A corresponding hearing aid is also provided.

Abstract: A hearing apparatus has artifact-free, fast feedback cancelation properties. The hearing apparatus has a first microphone coupled by way of a pre-whitening filter to a feedback canceler in a first hearing device. The hearing apparatus is configured to set a frequency response of the pre-whitening filter in dependence on a signal of a second microphone of the hearing apparatus.

Abstract: A system of signal processing an input signal in a hearing assistance device to avoid entrainment wherein the hearing assistance device including a receiver and a microphone, the method comprising using an adaptive filter to estimate an acoustic feedback path from the receiver to the microphone, generating one or more estimated future pole positions of a transfer function of the adaptive filter, analyzing stability of the one or more estimated pole positions for an indication of entrainment and adjusting the adaptation of the adaptive filter based on the stability.

Abstract: A method and a hearing device for cancelling or preventing feedback are disclosed. The hearing device comprises a microphone (1), a transfer function (2) and a receiver (3), wherein the transfer function (2) defines relation between an input signal (12) of the hearing device and an output signal (13, 13?) of the hearing device. The method according to the present invention comprises the steps of estimating an external transfer function (21) of an external feedback path (11) defined by sound traveling from the receiver (3) to the microphone (1), estimating the input signal (12?) having no feedback components of the external feedback path (11) using an auxiliary signal (15), which does not comprise feedback components of the external feedback path (11), and using the estimated input signal (14) for estimating the external transfer function (21) of the external feedback path (11).

Abstract: A configuration and associated methods are used for detecting acoustic feedback in a hearing device. One embodiment contains a first feedback detection unit, which determines the probability of feedback, a second feedback detection unit, which determines a weighting factor, and an arithmetic unit, which multiplies the feedback probability by the weighting factor. As an alternative to determining the weighting factor, a threshold value may also be controlled. This offers the advantage of improved acoustic feedback detection by a combination of two different feedback detection methods.

Abstract: A shielding element and a decoupling element are integrated into a combined attenuation element. The shielding element may be a shielding foil, preferably made of copper. The attenuation element may include a flexible backing foil, preferably a plastic backing foil which supports the shielding foil. It may also include an adhesive layer with which the electronic component is affixed to a housing. The physical properties of all elements of the attenuation element are attuned to one another such that it simultaneously attenuates both electromagnetic alternating fields as well as mechanical oscillations.

Abstract: In a voice intelligibility enhancement system that controls a gain of a voice signal based on noise power and voice power of the voice signal generated by a voice signal generation unit, it is detected whether the voice power is equal to or greater than a predetermined level, noise power output when the voice power is less than the predetermined level is measured and stored, noise power to be output when the voice power exceeds the predetermined level is estimated to be the stored noise power, and gain of a voice signal is controlled on the basis of the voice power and the estimated noise power.

Abstract: A method of modelling a feedback path from a receiver to a microphone in a hearing instrument, includes applying an electronic probe signal with an increasing level as a function of time to the receiver for conversion of the electronic probe signal into an acoustic probe signal output by the receiver, monitoring values of a first quality parameter calculated based at least in part on recorded microphone output signal, and after the first quality parameter reaches a predetermined first threshold value, determining at least one parameter of the feedback path based at least in part on the recorded microphone output signal values.

Abstract: A system for adapting a hearing aid to a user includes a unit generating an image of the user's ear together with a model of the hearing aid, wherein the model of the hearing aid in-situ includes a physical model of the hearing aid inserted in the user's ear prior to generating the image. The system also generates a mesh based on the image, calculates acoustic response to a simulated acoustic signal in the mesh, calculates a frequency response curve for a fixed position in the mesh, and identifies an optimal position of a microphone of the hearing aid in-situ from the acoustic response. They system also includes a comparator configured to compare the frequency response curve for the fixed position in the mesh with a maximum frequency response curve for the mesh stored by the system.

Abstract: A method for controlling adaptation of a feedback suppression filter in a hearing aid comprises the step of suspending the adaptation of the feedback suppression filter when the level of a hearing aid reference signal is below a predetermined threshold. The invention further provides a hearing aid with a feedback suppression filter and with means for suspending adaptation of the feedback suppression filter.

Abstract: A hearing prosthesis includes both a hearing aid adapted to sense and amplify low frequency acoustic sound signals and a cochlear implant system adapted to sense high frequency acoustic sound signals. The hearing aid has a first microphone adapted to sense the low frequency acoustic sound signals, amplify these sensed low frequency acoustic sound signals, and present the resulting amplified low frequency acoustic sound signals in the ear canal of a user, thereby enabling the user to better hear these amplified sounds using his or her normal hearing processes. The cochlear implant system includes a second microphone adapted to sense the high frequency acoustic sound signals and selectively stimulate the inner ear with electrical stimulation that will be perceived as high frequency acoustic sound signals. Both the cochlear implant system and the hearing aid system are coupled to operate on the same ear of the user.

Abstract: Disclosed is a hearing device system comprising at least one hearing aid circuitry and at least one active noise cancellation unit, the at least one hearing aid circuitry comprises at least one input transducer adapted to convert a first audio signal to an electric audio signal; a signal processor connected to the at least one input transducer and adapted to process said electric audio signal by at least partially correcting for a hearing loss of a user; an output transducer adapted to generate from at least said processed electric audio signal a sound pressure in an ear canal of the user, whereby the generated sound pressure is at least partially corrected for the hearing loss of the user; the at least one active noise cancellation unit being adapted to provide an active noise cancellation signal adapted to perform active noise cancellation of an acoustical signal entering the ear canal in addition to said generated sound pressure, wherein the hearing device system further comprises a combiner unit adapted t

Abstract: This invention relates to a hearing instrument, which comprises a first microphone converting ambient sound to an ambient sound signal, a signal processor generating a processed sound signal based on the ambient sound signal, a controllable output stage generating a driving signal based on the processed sound signal and in accordance with a control signal, a speaker unit generating a sound in the ear canal based on said driving signal, a second microphone located in the ear canal of the user and converting the sound in the ear canal to the monitor sound signal, and a linearization stage comparing the processed sound signal and the monitor sound signal and generating the control signal based thereon.

Abstract: A method is described for reduction of occlusion effects in an acoustic appliance which closes an auditory channel, wherein an audio signal in the transmission path of the acoustic appliance is processed by a signal processing unit and is emitted via an output transducer, which is arranged in the auditory channel, as an acoustic signal. A resultant sound signal is then detected by an auditory channel microphone and is supplied to a variable loop filter which is arranged in a feedback loop of an occlusion reduction unit for the acoustic appliance. The output signal from the loop filter is injected into the transmission path of the audio signal. The occlusion reduction unit is in this case controlled adaptively, with at least one signal from the transmission path of the audio signal and/or from the feedback loop being used to control the loop filter for the occlusion reduction unit.

Abstract: An anti-feedback device includes an anti-feedback filter provided in a closed loop. The anti-feedback device down-samples a signal of specific band selected from an output signal of an adaptive target signal transfer system and a signal of the same band selected from an input signal of the transfer system, and a filtering coefficient of the adaptive filter is updated by use of the down-sampled signals. The filter controller controls a filtering characteristic of the anti-feedback filter so that a peak gain of a frequency of an amplitude characteristic within a specific band of a closed loop determined from the filtering coefficient of the adaptive filter is suppressed. Moreover, the filter controller estimates a gain of the closed loop outside the specific band from the amplitude characteristic in the specific band and controls the amount of suppression of the anti-feedback filter outside the band in accordance with a result of estimation.

Abstract: A portable communication device is disclosed. The portable communication device comprises a speaker adapted to be held to an ear of a user for conveying sound to the user, at least one sensor for sensing sound emanating from said sound conveyed to the user, and a control unit. The control unit is adapted to estimate, based on an electrical input signal supplied to an input port of the speaker and an electrical output signal received from an output port of the at least one sensor, a transfer characteristic from the input port of the speaker to the output port of the sensor. Furthermore, the control unit is adapted to estimate, based on the estimated transfer characteristic, a degree of sound leakage from the user's ear. A corresponding method is also disclosed.

Abstract: The invention relates to a multi-component hearing aid system, comprising at least one first component that is designed to be disposed on or in the ear of a patient for the purpose of generating and/or amplifying an auditory stimulus and at least one further component which can engage at least partially and/or temporarily in a wireless communication connection via which a data transmission can take place with the first component that is to be worn on or in the ear, wherein circuitry means are included which can place at least one source of interference contained in the hearing aid system at least during the transmission of data into an operating mode in which interference signals are coupled by said at least one source of interference into a receiver involved in the data transmission in a manner that is at least attenuated compared to the normal operating mode.

Abstract: The invention relates to an adjustable hearing aid to which at least one parameter which influences the response and amplification characteristics of the hearing aid can be adjusted, with means being included which carry out testing of the effectiveness of an adjustment of this parameter in the prevailing auditory situation, and means being included which, given the existence of a minimum effectiveness, enable the adjustment option of this parameter.

Abstract: A method and an associated hearing device are enabled for setting feedback suppression. The method includes determining feedback events, determining the frequency of the feedback events within a prescribed first period of time, and setting feedback suppression in accordance with the frequency of the feedback events. The hearing device is able to choose automatically between different feedback algorithms in accordance with the specific feedback situation so that an optimal sound and feedback quality can be achieved.

Abstract: A system of signal processing an input signal in a hearing assistance device to avoid entrainment wherein the hearing assistance device including a receiver and a microphone, the method comprising using an adaptive filter to estimate an acoustic feedback path from the receiver to the microphone, generating one or more estimated future pole positions of a transfer function of the adaptive filter, analyzing stability of the one or more estimated pole positions for an indication of entrainment and adjusting the adaptation of the adaptive filter based on the stability.

Abstract: A method for processing at least one first and one second input signal in a hearing aid, with the input signals being filtered to create intermediate signals, the intermediate signals being added to form output signals, the input signals being assigned to a defined signal situation, and with the signals being filtered as a function of the assigned defined signal situation.

Abstract: The invention relates to an audio processing system for processing an input sound to an output sound. The invention further relates to a method of estimating a feedback transfer function in an audio processing system. The object of the present invention is to provide an alternative scheme for minimizing feedback in audio processing systems.

Abstract: A sound provider for providing sound to a person's ear includes one or more terminals for receiving a first electrical signal and a first sound emitter operatively connected to the one or more terminals for outputting a sound corresponding to the first electrical signal. The sound provider also includes a sound receiver for receiving sound and outputting a corresponding, second, electrical signal, and a second sound emitter operatively connected to the sound receiver for outputting a sound corresponding to the second electrical signal.

Abstract: A method and hearing aid mold are provided for a hearing device with a first segment for insertion into the auditory canal of the user, a second segment, which projects into the concha of the user when inserted, and a vent, which runs from the first segment into the second segment. A vent opening, which may be enclosed by a titanium ring, is directed in the second segment toward the outer ear of the user, so that an exchange of air can be achieved between the auditory canal and the rear of the outer ear through an opening in the outer ear. Ventilation of the auditory canal from the rear of the outer ear reduces the risk of feedback.

Abstract: The hearing system (1) comprises a filtering unit (6) for improving a signal-to-noise ratio of an S+N-audio signal (S+N) composed of a desired audio signal (S) and a unwanted audio signal (N), which filtering unit (6) comprises an adaptive filter; an S+N-input for receiving said S+N-audio signal (S+N); an N*-input for receiving an N*-audio signal (N*), which is used as an estimate for said unwanted audio signal (N); and an S*-output for outputting an S*-audio signal (S*) obtained in dependence of said S+N-audio signal (S+N) and said N*-audio signal (N*), which is an approximation towards said desired signal (S); wherein the hearing system (1) comprises a selecting unit (2) operationally connected to said filtering unit (6) for selecting a first input audio signal (In1; In2; . . . ) from at least two input audio signals (In1, In2) and feeding said first input audio signal (In1; In2) either to said S+N-input or to said N*-input.

Abstract: This invention relates to a system (100) and method for synthesizing an audio input signal of a hearing device. The system (100) comprises a microphone unit (102) for converting the audio input signal to an electric signal, a filter unit (110) for removing a selected frequency band of the electric signal and pass a filtered signal, a synthesizer unit (118) for synthesizing the selected frequency band of the electric signal based on the filtered signal thereby generating a synthesized signal, a combiner unit (120) for combining the filtered signal and the synthesized signal so as to generate a combined signal, and finally an output unit (122, 124, 126) for converting the combined signal to an audio output signal.

Abstract: There is disclosed a sound processing device (300) configured to apply a frequency shift to at least one frequency component of a received sound signal and to amplify at least part of the received sound signal. The processing device (300) is also adapted to generate an estimated feedback signal for combination with the received sound signal via a phase inverting feedback canceller (314). Associated methods (400, 600) of processing a sound signal are also disclosed.

Abstract: Methods of monitoring sound pressure level are provided. A method of monitoring sound pressure level includes: measuring a first sound pressure level in the ear canal; measuring a second sound pressure level out of the ear canal; calculating a first sound pressure level dose using the first sound pressure level, where if the first sound pressure level is below a permissible sound level a recovery function is used to calculate the first sound pressure level dose; and calculating a second sound pressure level dose using the second sound pressure level.

Abstract: In order to reduce feedback in a hearing aid, a hearing aid receiver is provided that comprises a housing having an inside surface and an outside surface, a motor, an active armature that is attached to the motor and attached to the inside surface of the housing, the active armature being driven in a vibrational manner by the motor, and an external passive component that is attached to the outside surface of the housing, the external passive component designed to vibrate in a direction opposed to vibrations of the active armature. A corresponding method for operating such a hearing aid receives is also provided.

Abstract: The signal quality in a hearing apparatus and in particular in a hearing device featuring a plurality of input channels is to be improved. Provision is made for this purpose for a hearing apparatus with a plurality of input channel systems each for recording and preprocessing an input signal and for outputting a channel signal each and a central computing device for processing a plurality of channel signals of the input channel systems. At least one of the plurality of input channel systems can be controlled by the central computing device as a function of at least two of the plurality of channel signals. Local weighting or deactivation of input channel components can be performed by means of this feedback using central information from the computing device. The latter case additionally allows for power consumption to be reduced.

Abstract: The training of a hearing apparatus in respect of an individual adjustment is to be developed in a more user-friendly manner. To this end, provision is firstly made to automatically classify a hearing situation, to adjust a parameter of the signal processing facility of the hearing apparatus and to automatically learn the adjusted parameters for the current hearing situation. A temporal monitoring of the steps “classifying” and “adjusting” is however carried out here and the automatic learning is only triggered if the classified hearing situation and the adjustment of the parameters have not changed over a predetermined time period. This not only simplifies the training, but also enables a more rapid training by means of automatically triggered training events.

Abstract: Disclosed is a hearing aid, where at least part of the hearing aid is adapted to be inserted into an ear canal of a user such that one end of the hearing aid and the tympanic membrane in the ear canal define a residual space of the ear canal, the hearing aid comprising an ambient space input transducer adapted to convert ambient sound to an electric sound signal, when the ambient sound reaches the ear of a user from an ambient space, a processor connected to said ambient space input transducer and adapted to process said electric sound signal, an output transducer connected to said processor and adapted to convert said processed electric sound signal to a sound pressure in the residual space of the ear canal, and wherein the hearing aid further comprises a residual space input transducer connected to said processor and arranged to predominantly receive said sound pressure in the residual space, and wherein the residual space input transducer is adapted to convert said sound pressure to an electric residual sp

Abstract: This invention relates to a hearing instrument (100), which comprises a first microphone (102) converting ambient sound to an ambient sound signal, a signal processor (104) generating a processed sound signal based on the ambient sound signal, a controllable output stage (106) generating a driving signal based on the processed sound signal and in accordance with a control signal, a speaker unit (110) generating a sound in the ear canal based on said driving signal, a second microphone (116) located in the ear canal of the user and converting the sound in the ear canal to the monitor sound signal, and a linearization stage (108) comparing the processed sound signal and the monitor sound signal and generating the control signal based thereon.

Abstract: A hearing aid comprises a noise suppressor that calculates noise suppression gain, an adjustment amount calculator that calculates an adjustment amount on the basis of a signal strength and a noise component strength, and a nonlinear compressor that calculates a reference gain on the basis of a signal strength and specific reference gain information and adjusts the reference gain on the basis of an adjustment amount, thereby calculating a nonlinear compression gain.

Abstract: In one aspect, a hearing device is provided with a multi-stage activation circuit including a primary activation unit, an evaluation unit and a main activation unit. The primary activation unit monitors a sound-induced input level and forwards incoming signals to the evaluation unit when a threshold value of the input level is exceeded. The evaluation unit is activated when the threshold value is exceeded and determines a feature of incoming signals suitable for identifying and/or classifying a sound causing the incoming signals. The main activation unit is activated, for example, when the feature determined by the evaluation unit indicates a noise that should be perceptible to the wearer of the hearing device. The main activation unit activates further components of the hearing device including the signal processing and amplification circuit and the output unit.

Abstract: A system and method that reduces the perceptual effect resulting from ear occlusion include an electro-acoustic feedback network that produces phase canceling sounds in the ear, where a receiver and a microphone are located. A control mechanism controls the response of the feedback network to minimize distortion in the ear while maintaining a desired frequency response for external signals. Devices producing the external signal include hearing aids, personal sound devices, in ear monitors, communications headsets and hearing protectors. The integration of the above with these devices improves a user's perception of their own voice.

Abstract: There is described a method for operation of a hearing device system with two microphones arranged spatially separated from one another and with sound-generating output units assigned to these microphones, in which, by comparison of the microphone signals or of signals derived therefrom, feedback is detected, and on detection of the feedback measures are initiated for reducing the feedback, and with the comparison of the microphone signals or of signals derived therefrom comprising a frequency-selective power comparison. There is also described a hearing device system suitable for this method.

Abstract: Method and apparatus for entrainment containment in digital filters using output phase modulation. Phase change is gradually introduced into the acoustic feedback canceller loop to avoid entrainment of the feedback canceller filter. Various embodiments employing different output phase modulation approaches are set forth and time and frequency domain examples are provided. Additional method and apparatus can be found in the specification and as provided by the attached claims and their equivalents.

Abstract: A hearing aid which achieves a comfortable feeling to use while preventing generation of howling includes a microphone for converting an environmental sound to an electric signal, a hearing aid processor for hearing aid processing of an output signal of the microphone, an earphone for converting an output signal of the hearing aid processor to a sound signal, an external ear canal microphone converting a sound within an external ear canal to an electric signal, and an adaptive filter for comparing an output signal of the external ear canal microphone and the output signal of the hearing aid processor to automatically adjust the output signal of the hearing aid processor in such a manner that the output signal of the external ear canal microphone approaches the output signal of the hearing aid processor.

Abstract: A system for reducing an echo and/or a residual echo in a microphone output signal includes an echo compensation filter configured to receive audio input signals and generate an estimated echo signal. A speech activity detector is configured to detect speech of a local speaker, and a combining circuit is configured to generate an echo compensated signal by subtracting the estimated echo signal from the microphone output signal. A residual echo reduction circuit is configured to suppress the residual echo in the echo compensated signal based on the detected speech activity, and output an echo suppressed output signal. The echo reduction system may reduce local background noise and residual echoes in a microphone output signal so that local speech may be transmitted free from undesirable signals.

Abstract: This document provides a hearing assistance device for playing processed sound inside a wearer's ear canal, the hearing assistance device comprising a first housing, signal processing electronics disposed at least partially within the first housing, a first microphone connected to the first housing, the first microphone adapted for reception of sound, a second microphone configured to receive sound from inside the wearer's ear canal when the hearing assistance device is worn and in use and microphone mixing electronics in communication with the signal processing electronics and in communication with the first microphone and the second microphone, the microphone mixing electronics adapted to combine low frequency information from the first microphone and high frequency information from the second microphone to produce a composite audio signal.