A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing)


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In the literature the PBF filter structure is also known as a Farrow structure. Farrow proposed a fractional delay FIR filter structure where every coefficient of an FIR filter could be expressed as an Nth order polynomial in the delay parameter D. Even if the Taylor polynomial has been applied in the illustrations of this invention, this invention is not limited by the applied polynomial basis functions.

Numerical properties of the DCD-RLS algorithm for stereo acoustic echo cancellation

The configuration of the system according to FIG. At the input side, there is an input block - 1 provided for comprising a plurality of microphones 1 to M, where M is a number of channels matching in this embodiment with the number of microphones , exemplarily shown as - 1 , - 1 , 8 M 0 - 1 and a pre-processing stage - 1. Note that the nomenclature of reference signs reflects the respective channels insofar. In said pre-processing stage - 1 , a plurality of amplifiers may be provided not shown, but would be named - 1 , - 1 , 8 M 2 - 1.

As to said amplifiers, they may comprise typical additional circuits suitable for example for a signal conditioning, like input-matching, amplitude limiting, compression, adaptive automatic gain control, adaptive bandwidth selection, parametric or adaptive equalising, ground lifting, phase inversion or shifting, symmetrical, non-symmetrical or differential input, phantom voltage, muting.

Furthermore, said pre-processing stage - 1 comprises a plurality of signal converters, said converters are suitable for an analog-to-digital conversion, for example by a pulse code modulation using at least a bit, an oversampling, a decimation filter, noise or spectral shaping.

Note that analog-to-digital conversion may be done also by a digital-to-analog converter. Also, one converter can process multiple channels having a multiplexer doing a channel scanning and providing buffers and a queuing, priority or a rule based scheme for operating or processing multiple channels. Also, a sampling, be it equidistant or not, single- or multi-valued, including variable oversampling of every channel may be performed by a deterministic, cyclic, rule- or signal-dependent or time-variant basis using for example a index driven scanning of one to every of a plurality of channels with a sampling rate, for example, n times the bandwidth of a single channel, where n may be a number of active channels.

Note by the way, that a so-called intelligent microphone may be realised by using a signal processor right behind a sonic transducer, Antenna, doing all before-said signal conditioning features in a signal domain, by doing direct sampling without input filter. Said input stage can also be substituted by an output of another signal processor delivering or passing a data structure, for example in a mobile terminal device suitable for a measurement device or an electronic musical instrument having a Musical Instruments Digital Interface.

Next, a main signal processing stage - 1 comprises a plurality of pre-filter blocks - 1 , - 1 , 9 M 0 - 1 , said blocks being suitable for pre-filtering; an AEC block - 1 having a plurality of N blocks - 1 , - 1 , 10 N 0 - 1 each capable of acoustic echo cancelling; and a post-filter - 1 having a plurality of N- 1 operation means - 1 , - 1 ,.

Each of said pre-filters - 1 , - 1 , 9 N 0 - 1 has a first, a second,. W N,M z , respectively, where M is said number of channels, N is the number of filters within each channel corresponding to the N- 1 order polynomial of the PBF. Such a multi-dimensional filter may be named a matrix filter arrangement or an arrangement of a filter matrix.

Aforesaid behavior may include a variable negative-exponential, a variable positive-exponential, a linear, smoother or quantised behavior so as to form adaptive or dynamic filter coefficients which may updated in a process realtime. Each of said pre-filter block - 1 , - 1 , 9 N 0 - 1 has an associated output function W 1 z , W 2 z ,. Note, that although W i,M z may be a time-invariant function, it can also be time variant not shown , for example—either by doing individual feedback per channel, for example, by connecting the output of each block with the input, by providing a suitable scaling, damping or inverting element to avoid saturation, clipping, oscillation or latch-up—or by feeding back an output of the respective operation member, for example 91 S- 1 to each of the blocks within said pre-filter - 1 or to any other block or any combination of said pre-filter blocks - 1 , - 1 , 9 N 0 - 1.

Each of plurality of said blocks - 1 , - 1 , 10 N 0 - 1 is suitable for acoustic echo cancelling, for example by providing a function H 1 z , H 2 z ,.

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H i z may be an impulse response function or distribution in the signal decomposition to the frequency domain using for example a Fourier transform or some other exact or approximated signal decomposition method such as an orthogonal transform, a lapped orthogonal transform, a Wavelet transform, or a filter bank; a spectral impulse response, a inverse function in the z-Domain or in the k-Domain, in a secret Domain, a cepstrum function, a function or a probability distribution, a variance, correlation, cross-correlation, inverse correlation, an autocorrelation function, a transcendental, higher-dimensional or non-unique function, a mapping, a memory structure, a data or spectral signal, a signature, a fragment of a memory structure or a spectrum out of dimension.

Also H i z may or may not obey a Parseval theorem of quadratically integrable functions or Sommerfeld radiation condition or have a smooth or non-smooth not carrier. Lastly H i z may contain a delta distribution, including its higher order derivatives. The main processing stage - 1 comprises also a post-filter for polynomial beamforming - 1 suitable for providing a function H Farrow z,D of beam steering network of steering parameter D, comprising signal amplification operation means - 1 , - 1 ,. Note that the beam steering network of the post-filter - 1 may be realised to have no or a neglectable inherent processing delay or latency.

Said beam steering network may be suitable for delay of a certain time or clock cycles. Different beam steering networks may be even time or amplitude variant, programmable or have one or a plurality of for example weighted or weighting feedback inputs including scaling, inverting etc not shown. At the output side, generally, there is a post-processing stage - 1 , for example having similar to the input stage - 1 at least an amplifier not shown and at least one signal converter not shown for a digital-to-analog conversion; and more than one of a plurality of a speaker not shown.

In this first embodiment the output section is simplified by for comprising only one speaker. But may be appreciated that the features substantiated for the input side, especially for the signal converters are also applicable for the output side. Note that the signal converter may be a part of a signal processor or semiconductor of a type capable to output a power signal directly to a speaker, for example using a high-clocked 1 bit data signal feeding a pulse width modulation power amplifier, wherein the speaker or the frequency response of the environment may acts as reconstruction low pass.

In FIG. Note that the foregoing example for a matrix connection may also be an example for a method for sequential processing or addressing, for example a matrix addressing method for processing the whole structure, which also can be applied reversed, or reshaped matrix form, including all operations possible with matrices. Also, if aforesaid addressing may be performed continuously within a programming loop or a procedure, an index shifting in a circle, a index permutation or random index modulation is possible.

For an example an index-rotate left of 1, 2,. M means the order M, 2. Now, each output of each pre-filter - 1 , - 1 ,. Also, the respective outputs from the AEC blocks - 1 , namely from - 1 , - 1 ,. Each output of said operation members 91 T- 1 , 92 T- 1 ,.

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Said feedback channels contain the information about the residual echo characteristics which is utilized in AEC filter adaptation. Also, according to FIG. In the post-filter - 1 , each output of each amplification element is connected with the input of the operation member of next lower N, the N- 1 -th operation member, such that each amplification element and each combining operation member are connected in an alternating manner as is shown in FIG. Said sequential connection may be implemented efficiently using multiply-accumulate DSP processing instructions with a common accumulator memory for the creation of the output signal y k.

The output of the first operation member - 1 of the post-filter - 1 signal y k is a near-end signal output leaving the system and which may be connected to a network or a further processing stage not shown. Running through said network, internet etc. The inputs of all members - 1 , - 1 ,. Said input channel is also connected to said post-processing stage - 1 , comprising said speaker. When said pre-filter beam patterns are combined by the post-filter the overall beam pattern of the PBF is achieved for the desired beam steering direction illustrated in FIG.

In a typical product configuration the relative positions of the microphones and loudspeakers are fixed. That means that the direction of arrival for the direct sound from the loudspeaker to microphone can be estimated during the time design time of the product. It is possible to design the minimum sensitivity of the microphone array towards the dominant interfering sources i.

Low level echo coupling has many benefits, which can be utilized e. In a mobile terminal device typically a processing unit, for example a signal processor and memory unit are prepared for providing an acoustic echo cancellation and a microphone beamforming. There are one or a plurality of microphones At an input side, a pre-processing stage comprises an amplifier for amplifying an audio signal and a signal converter for an analog-to-digital conversion.

Said acoustic echo cancellation and a microphone beamforming are performing within a main signal processing stage In stage , a pre-filter for polynomial beamforming , an acoustic echo cancellation stage and a post-filter for polynomial beamforming are provided as components, for example by using a bus of N channels, or a function having an Index for addressing N channels. There may be individual feedback loops for each component, including inverter or scaling blocks. Also, at an output side, a loudspeaker system processing stage may comprise an amplifier and a signal converter for a digital-to-analog conversion and one or a plurality of a speaker For example, an acoustic echo cancellation control stage controlling e.

Also, a speaker tracing stage , suitable for estimation of Direction of Arrival of a signal may be provided as well as a beam steering and beam shape control stage which is connected to post-filter for polynomial beamforming Furthermore an adaptive noise reduction stage suitable for adaptive interference cancellation or some other noise reduction scheme such as spectral subtraction, wherein said stage may be located between the output of said post-filter stage and the output of the main signal processing stage Said stage may be connected to the stage by a plurality of J channels, and the stage may be connected to the output by a plurality of R channels.

Possibly, the said adaptive noise reduction stage may be arranged before any of the components in the main processing stage or work in parallel with one of the components. Note further that any of components, pre-filter stage , audio echo cancellation stage and post-filter stage or said adaptive noise reduction stage , may be permutated in a signal flow from left to right within signal processing stage Also the internal structure of the signal processing stage may be changed even during runtime, including the number of processed channels, any parameters of the channel, for example bandwidth or resolution, number of processed coefficients.

If the audio processing flow is correct interfering signal components have been removed from the signals before the audio processing control takes place. In addition to the mentioned benefits of the AEC control the above configuration provides clear benefits in enabling e. The proper suppression of the strong interfering echo signals simplify the control logic and improve the CPU efficiency. In general digital signal processors are very efficient in running FIR filters in comparison to running conditional execution logic that is typical in a control code.

True benefits will be dependent on the final system configuration and required system performance. For the rest the same components are used as shown in FIG. According to FIG. This MIMO implementation calls for multi-channel echo cancellation methods known in the art. With this configuration the total number of AEC filters can be reduced so that steering independent AECs H i z will take care of the dominant echo components and the AEC filter s G z will attenuate the residual echo leakage from the steering independent AECs H i z as well as the unattenuated echo from the pre-filter output channels intermediate signal without a dedicated AEC block.

Weitere Formate

Said fourth embodiment can also be extended for multiple beams and output signals see FIG. This embodiment can also be extended for multiple beams and output signals see FIG. The number of intermediate signals is dependent on the order of the steering polynomial of the PBF, which is independent of the microphone number. As an example first order differential beam pattern supporting full 3D steering can be constructed with four intermediate signals having orthogonal pre-filter beams.

If the steering angle is reduced into half-space or a 2D plane the total number of required intermediate signal and N can be further reduced. Similarly it would be possible to construct e. The increase in the polynomial order can be utilized in more accurate polynomial approximation of the ideal Filter-and-Sum beamforming FSB filter coefficient.

European patent EP granted Jun. The beam pattern of the pre-filter W i z may enable direction dependent AEC control, because different pre-filters have different directivity patterns and therefore the echo coupling factors may be also dependent of the directivity of the pre-filter. The residual echo levels would be weighted according to the beamformer's beam pattern enabling direction dependent AEC control. Post-filtering may also attenuate the residual echo level due to the summation of multiple incoherent residual echo signals present in the input signals of the post-filter.

This can be justified because direct sound coupling can be designed—a priori—in the PBF filter design. If one of the AEC filter's has e. The implementation with a shortened AEC for the direct sound can be configured quite easily with the partitioned AEC structure. The PBF filter using Taylor polynomials has a very simple post-filter processing network, but with high order polynomial approximation the pre-filter coefficients may become numerically undesirably large and the polynomial approximation errors may grow large between the interpolation points. These characteristics are well known for Taylor polynomials and Lagrange interpolation in the mathematics literature.

This makes Chebyshev polynomial approximation a very suitable for PBF application. The invention can be implemented in the frequency domain as well as with subband processing utilizing filter banks. These both could be very feasible implementations especially for wide band beamforming systems no illustrative figures available yet. It is possible to integrate speaker tracking functionality to the intermediate signals after the AEC processing. This has the advantage of being more robust against the disturbances cause by the echo signal from the loudspeaker.

In the current implementation strong echo reflections can cause speaker tracker algorithm to turn towards the reflected echo sound, which could cause severe artifacts especially during the double talk. The present invention is not limited by the AEC technology. In this case the CPU benefit from this invention is already neutral. Therefore the benefits are already neutral in the lowest complexity implementations. Effective date : In a mobile terminal device having a processing unit and a memory unit, an acoustic echo cancellation and a microphone beamforming are provided.

Said device includes a plurality of a microphones, a pre-processing stage has an amplifier and a signal converter for an analog-to-digital conversion. In a main signal processing stage, a pre-filter suitable for polynomial beamforming, an acoustic echo cancellation stage and a post-filter for polynomial beamforming are provided.

Furthermore, a post-processing stage has an amplifier and a signal converter for a digital-to-analog conversion, and plurality of speakers. AREA OF THE INVENTION The present invention generally relates to a cancellation of an acoustic signal, for example a cancellation of an acoustic echo or feedback frequencies in a room and to a beamforming including beam steering , for a plurality of microphones, for example an array of microphones, for example in mobile communications.

The configuration of the system is as follows: On the input side, there is an input block 5 provided for comprising a plurality of microphones 10 , 20 , A device comprising: a pre-filter for polynomial beamforming, wherein the pre-filter comprises a plurality of finite impulse response filters that do not change an echo path of a signal;. The device according to claim 1 , wherein said signal processing stage comprises a time-invariant beamforming stage.

The device according to claim 1 , wherein said device comprises a time-variant beamforming stage. The device according to claim 1 , wherein said pre-filter is time-invariant and is suitable for time-invariant beamforming and wherein said post-filter is time-variant and is suitable for time-variant beam steering.

The device according to claim 1 , further comprising: a plurality of microphones operable to receive an acoustic signal using microphone beamforming.

The device according to claim 5 , further comprising: a pre-processing stage comprising a plurality of analog-to-digital signal converters, wherein the pre-processing stage is connected to the plurality of microphones and the main-signal processing stage. The device according to claim 6 , wherein the pre-processing stage further comprises a plurality of amplifiers. The device according to claim 1 , further comprising: a loudspeaker system processing stage comprising at least one amplifier and at least one digital-to-analog signal converter; and.

The device according to claim 1 , wherein the polynomial beamforming performed by the pre-filter and polynomial beamforming performed by the post-filter apply polynomial basis functions based on Chebyshev polynomials. The device according to claim 1 , wherein each finite impulse response filter of the pre-filter has a dedicated beam pattern, wherein the post-filter is operable to achieve an overall beam pattern of the polynomial beamforming for a desired beam steering direction. The device according to claim 1 , further comprising: an acoustic echo cancellation controller connected to the acoustic echo cancellation stage and operable to control an acoustic echo cancellation adaptation rate using a voice activity detector.

The device according to claim 5 , further comprising: a speaker tracing controller connected to the acoustic echo cancellation controller and the post-filter, wherein the speaker tracing controller is operable to estimate direction of arrival of the received acoustic signal.

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The device according to claim 1 , further comprising: a beam steering and beam shape controller connected to the post-filter. The device according to claim 1 , further comprising: an adaptive noise reduction stage operable to perform adaptive interference cancellation. The device according to claim 1 , wherein the post-filter comprises a plurality of parallel post-filter stages operable to track multiple dynamic sources. The device according to claim 1 , wherein the at least one speaker comprises a plurality of speakers, wherein the audio signal that is to be output via the plurality of speakers comprises a multiple-input multiple output audio signal, wherein the acoustic echo cancellation stage is operable to perform multi-channel echo cancellation.

The device according to claim 1 , wherein the plurality of processing blocks of the acoustic echo cancellation stage comprise a plurality of first processing blocks that are independent of the beam steering processing function applied by the post-filter, wherein the acoustic echo cancellation stage further comprises at least one second processing block that is not independent of the beam steering processing function applied by the post-filter. The device according to claim 17 , wherein the plurality of first processing blocks operate on dominant echo components, wherein the at least one second processing block operates on residual echo leakage from the plurality of first processing blocks, wherein the at least one second processing block further operates on unattenuated echo from the plurality of third outputs.

The device according to claim 17 , wherein the plurality of processing blocks of the acoustic echo cancellation stage comprise a plurality of first processing blocks that are independent of the beam steering processing function applied by the post-filter, wherein the acoustic echo cancellation stage further comprises at least one second processing block that is not independent of the beam steering processing function applied by the post-filter.

The device according to claim 1 , wherein the acoustic echo cancellation stage operates on at least one output of the pre-filter and provides at least one input for the post-filter. The device according to claim 1 , wherein the device comprises a mobile device. The device according to claim 1 , wherein the device comprises a mobile terminal device. The device according to claim 1 , wherein the device comprises a mobile communication device.

The device according to claim 6 , wherein said plurality of microphones comprises an array of microphones that is connected to M input-channels of said pre-processing stage, wherein said pre-processing stage has M output-channels connected to N input-channels of said signal processing stage. The device according to claim 24 , wherein said signal processing stage has J output-channels which are connected to J input-channels of a network. A device comprising: a plurality of processing blocks each of which is operable to perform acoustic echo cancellation by applying an acoustic echo cancellation function based on an audio signal that is to be output via at least one speaker, wherein the plurality of processing blocks are located within an acoustic echo cancellation stage that operates after a pre-filter and before a post-filter, wherein the pre-filter is for polynomial beamforming and does not change an echo path of a signal on which the pre-filter operates, wherein the post-filter is for polynomial beamforming and applies a beam steering processing function.

The device according to claim 26 , wherein said pre-filter is time-invariant and is suitable for time-invariant beamforming and wherein said post-filter is time-variant and is suitable for time-variant beam steering. The device according to claim 26 , wherein the polynomial beamforming performed by the pre-filter and polynomial beamforming performed by the post-filter apply polynomial basis functions based on Chebyshev polynomials.

The device according to claim 26 , further comprising: an acoustic echo cancellation controller connected to the acoustic echo cancellation stage and operable to control an acoustic echo cancellation adaptation rate using a voice activity detector. The device according to claim 26 , further comprising: a speaker tracing controller connected to the acoustic echo cancellation controller and the post-filter, wherein the speaker tracing controller is operable to estimate direction of arrival of the received acoustic signal. The device according to claim 26 , wherein the at least one speaker comprises a plurality of speakers, wherein the audio signal that is to be output via the plurality of speakers comprises a multiple-input multiple output audio signal, wherein the acoustic echo cancellation stage is operable to perform multi-channel echo cancellation.

The device according to claim 26 , wherein the plurality of processing blocks of the acoustic echo cancellation stage comprise a plurality of first processing blocks that are independent of the beam steering processing function applied by the post-filter, wherein the acoustic echo cancellation stage further comprises at least one second processing block that is not independent of the beam steering processing function applied by the post-filter.

The device according to claim 32 , wherein the plurality of first processing blocks operate on dominant echo components, wherein the at least one second processing block operates on residual echo leakage from the plurality of first processing blocks, wherein the at least one second processing block further operates on unattenuated echo from the plurality of third outputs. The device according to claim 32 , wherein the plurality of processing blocks of the acoustic echo cancellation stage comprise a plurality of first processing blocks that are independent of the beam steering processing function applied by the post-filter, wherein the acoustic echo cancellation stage further comprises at least one second processing block that is not independent of the beam steering processing function applied by the post-filter.

The device according to claim 26 , wherein the acoustic echo cancellation stage operates on at least one output of the pre-filter and provides at least one input for the post-filter. The device according to claim 26 , wherein the device is embodied in a mobile device. The device according to claim 26 , wherein the device is embodied in a mobile terminal device.

The device according to claim 26 , wherein the device is embodied in a mobile communication device. USP true Acoustic echo cancellation for time-varying microphone array beamsteering systems. USB1 en. Beamforming apparatus and method based on long-term properties of sources of undesired noise affecting voice quality. USB2 en. Acoustic echo cancellation for microphone array with dynamically changing beam forming.

Methods and apparatuses for echo cancellation with beamforming microphone arrays. Adaptive acoustic echo canceller having means for reducing or eliminating echo in a plurality of signal bandwidths. EPA1 en.

Cyberon's Acoustic Echo Cancellation Solution

System and method for processing a signal being emitted from a target signal source into a noisy environment. Kajala M. Dispatched from the UK in 2 business days When will my order arrive? Franz Zotter. Amar Mitiche. Jacob Benesty. Sharon Gannot. Orhan Gazi. Boaz Rafaely. Jagannath Malik.


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Mohammad Ali Nematollahi. Home Contact us Help Free delivery worldwide. Free delivery worldwide. Bestselling Series. Harry Potter. Popular Features. New Releases. Microphone Array Signal Processing. Description In the past few years we have written and edited several books in the area of acousticandspeechsignalprocessing.

Thereasonbehindthisendeavoristhat there were almost no books available in the literature when we? According to all the feedback we have received so far, we can say that we were right in doing this. Recently, several other researchers have followed us in this journey and have published interesting books with their own visions and perspectives. The idea of writing a book on Microphone Array Signal Processing comes from discussions we have had with many colleagues and friends.

As a c- sequence of these discussions, we came up with the conclusion that, again, there is an urgent need for a monograph that carefully explains the theory and implementation of microphone arrays. While there are many manuscripts on antenna arrays from a narrowband perspective narrowband signals and narrowband processing , the literature is quite scarce when it comes to s- sor arrays explained from a truly broadband perspective. Many algorithms for speech applications were simply borrowed from narrowband antenna - rays.

However, a direct application of narrowband ideas to broadband speech processing may not be necessarily appropriate and can lead to many m- understandings. Product details Format Hardback pages Dimensions x x Illustrations note 2 Tables, black and white; 39 Illustrations, black and white; X, p. Other books in this series.

A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing) A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing)
A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing) A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing)
A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing) A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing)
A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing) A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing)
A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing) A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing)
A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing) A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing)
A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing) A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing)
A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing) A Perspective on Stereophonic Acoustic Echo Cancellation: 4 (Springer Topics in Signal Processing)

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