Acoustic echo canceller using MDF algorithm. More...

#include <MDFEchoCancellation.h>

Inheritance diagram for MDFEchoCancellation< Allocator >:

Public Member Functions
	MDFEchoCancellation (int filterLength, AudioFFTBase &fftDriver, const Allocator &alloc=Allocator())

	MDFEchoCancellation (int filterLength, int nbMic, int nbSpeakers, AudioFFTBase &fftDriver, const Allocator &alloc=Allocator())

	~MDFEchoCancellation ()

virtual void	addNotifyAudioChange (AudioInfoSupport &bi)
	Adds target to be notified about audio changes.

virtual AudioInfo	audioInfo () override
	provides the actual input AudioInfo

virtual AudioInfo	audioInfoOut ()

virtual int	available () override

virtual int	availableForWrite () override

virtual bool	begin ()

void	cancel (const echo_int16_t rec, const echo_int16_t play, echo_int16_t *out)

void	capture (const echo_int16_t rec, echo_int16_t out)

virtual void	clearNotifyAudioChange ()
	Deletes all change notify subscriptions.

int	control (int request, void *ptr)

virtual void	end ()

virtual void	flush () override

int	getFilterLength ()

int	getFrameSize ()

void	getImpulseResponse (echo_int32_t *response)

int	getImpulseResponseSize ()

int	getMicChannels ()

int	getSamplingRate ()

int	getSpeakerChannels ()

EchoState *	getState ()

bool	isNotifyActive ()
	Checks if the automatic AudioInfo update is active.

virtual	operator bool ()

void	playback (const echo_int16_t *play)

virtual size_t	readBytes (uint8_t *data, size_t len) override

virtual size_t	readSilence (uint8_t *buffer, size_t length)
	Source to generate silence: just sets the buffer to 0.

virtual bool	removeNotifyAudioChange (AudioInfoSupport &bi)
	Removes a target in order not to be notified about audio changes.

void	reset ()

virtual void	setAudioInfo (AudioInfo newInfo) override
	Defines the input AudioInfo.

void	setFFTDriver (AudioFFTBase &fftDriver)

void	setFilterLength (int len)

void	setMicChannels (int num)

void	setNotifyActive (bool flag)
	Deactivate/Reactivate automatic AudioInfo updates: (default is active)

void	setSamplingRate (int rate)

void	setSpeakerChannels (int num)

void	setWriteBufferSize (int size)

virtual size_t	write (const uint8_t *data, size_t len) override

virtual size_t	write (uint8_t ch) override

virtual void	writeSilence (size_t len)
	Writes len bytes of silence (=0).

Protected Member Functions
template<typename T >
T *	echoAlloc (size_t count)
	Allocate memory for array of type T using custom allocator.

void	echoCancellationImpl (EchoState st, const echo_int16_t in, const echo_int16_t far_end, echo_int16_t out)
	Core echo cancellation implementation.

void	echoFatal (const char *str)

template<typename T >
void	echoFree (T *ptr, size_t count=0)
	Deallocate memory using custom allocator.

EchoState *	echoStateInitMc (int frame_size, int filter_length, int nb_mic, int nb_speakers)
	Initialize multi-channel echo canceller state.

void	echoWarning (const char *str)

void	ensureInitialized ()
	Ensure echo canceller is initialized (lazy initialization)

void	filterDcNotch16 (const echo_int16_t in, echo_word16_t radius, echo_word16_t out, int len, echo_mem_t *mem, int stride)
	Apply DC notch filter to remove DC offset.

void	mdfAdjustProp (const echo_word32_t W, int N, int M, int P, echo_word16_t prop)
	Adjust proportional adaptation weights.

echo_word32_t	mdfInnerProd (const echo_word16_t x, const echo_word16_t y, int len)
	Compute inner product of two vectors.

virtual int	not_supported (int out, const char *msg="")

void	notifyAudioChange (AudioInfo info)

void	powerSpectrum (const echo_word16_t X, echo_word32_t ps, int N)
	Compute power spectrum from FFT output.

void	powerSpectrumAccum (const echo_word16_t X, echo_word32_t ps, int N)
	Accumulate power spectrum from FFT output.

void	refillReadBuffer ()
	Refill small read buffer (e.g. 8 bytes) to avoid single byte reads when calling read()

void	spectralMulAccum (const echo_word16_t X, const echo_word32_t Y, echo_word16_t *acc, int N, int M)
	Accumulate spectral multiplication across multiple frames.

float	spxCos (float x)
	Compute cosine function.

float	spxExp (float x)
	Compute exponential function.

echo_int16_t	spxIlog2 (echo_uint32_t x)

float	spxSqrt (float x)

void	weightedSpectralMulConj (const echo_float_t w, const echo_float_t p, const echo_word16_t X, const echo_word16_t Y, echo_word32_t prod, int N)
	Compute weighted spectral multiplication with conjugate.

Protected Attributes
int	_timeout = 10

Allocator	allocator

AudioFFTBase *	fft_driver

int	filter_length

AudioInfo	info

bool	initialized = false

bool	is_notify_active = true

int	nb_mic

int	nb_speakers

Vector< AudioInfoSupport * >	notify_vector

EchoState *	state = nullptr

RingBuffer< uint8_t >	tmp_in {0}

RingBuffer< uint8_t >	tmp_out {0}

int	write_buffer_size = MAX_SINGLE_CHARS

Detailed Description

template<typename Allocator = std::allocator<uint8_t>>
class audio_tools::MDFEchoCancellation< Allocator >

Acoustic echo canceller using MDF algorithm.

High-performance echo cancellation implementation based on the Multi-Delay block Frequency adaptive filter (MDF) algorithm. Supports both single and multi-channel configurations with customizable memory allocation.

The echo canceller operates by:

Learning the echo path between loudspeakers and microphones
Adaptively filtering the playback signal to predict the echo
Subtracting the predicted echo from the captured microphone signal

Features:

Header-only C++ implementation
Custom allocator support for embedded systems
Fixed-point and floating-point arithmetic modes
Two-path filter for improved double-talk handling
Multi-channel support (multiple microphones and speakers)

Template Parameters

Allocator Custom allocator type for memory management (defaults to std::allocator<uint8_t>)

Note: This implementation requires an external FFT driver implementing the AudioFFTBase interface from AudioFFT.h

Example usage:

FFTDriverImpl fftDriver;
EchoCanceller<> echo(frameSize, filterLength, fftDriver);
echo.setSamplingRate(16000);
echo.cancellation(micData, speakerData, outputData);

Member Function Documentation

◆ addNotifyAudioChange()

virtual void addNotifyAudioChange ( AudioInfoSupport & bi )

inlinevirtualinherited

Adds target to be notified about audio changes.

Reimplemented in CodecNOP, EncodedAudioOutput, EncodedAudioStream, AACDecoderFDK, DecoderBasic, CodecChain, MP3DecoderHelix, MP3DecoderMAD, OggContainerDecoder, RTSPClient< TcpClient, UdpSocket >, Pipeline, and Pipeline::ModifyingStreamAdapter.

◆ audioInfo()

virtual AudioInfo audioInfo ( )

inlineoverridevirtualinherited

provides the actual input AudioInfo

Implements AudioInfoSupport.

Reimplemented in JupyterAudioT< T >, MozziStream, TimerCallbackAudioStream, EncodedAudioStream, PureDataStream, AdapterAudioOutputToAudioStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, and InputMerge< T >.

◆ audioInfoOut()

virtual AudioInfo audioInfoOut ( )

inlinevirtualinherited

provides the actual output AudioInfo: this is usually the same as audioInfo() unless we use a transforming stream

Reimplemented in PureDataStream, PWMAudioOutput, ChannelFormatConverterStreamT< T >, ChannelFormatConverterStream, NumberFormatConverterStreamT< TFrom, TTo >, NumberFormatConverterStream, FormatConverterStream, Pipeline, ResampleStream, and ResampleStreamT< TInterpolator >.

◆ available()

virtual int available ( )

inlineoverridevirtualinherited

Reimplemented from Stream.

Reimplemented in AudioKitStream, AudioLoRa, URLStreamBufferedT< T >, URLStreamBufferedT< ICYStream >, VBANStream, AudioStreamWrapper, LoRaStream, FaustStream< DSP >, AudioFFTBase, AudioMP34DT05, I2SCodecStream, MiniAudioStream, StdioStream, TfLiteAudioStream, A2DPStream, ESPNowStream, HammingFEC< bytecount, block_t >, HLSStreamT< URLStream >, HttpRequest, ICYStreamT< T >, URLStream, BufferedTaskStream, ReedSolomonFEC< bytecount, additional_bytes >, UDPStream, AnalogAudioArduino, AnalogAudioStream, AudioEffectStreamT< T >, Equalizer3Bands, Equalizer3BandsPerChannel, I2SStream, ReformatBaseStream, TimedStream, MemoryStream, RingBufferStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, BufferedStream, ConverterStream< T >, MeasuringStream, ProgressStream, Throttle, InputMerge< T >, CallbackStream, FilteredStream< T, TF >, FilteredStream< int16_t, int16_t >, ChannelFormatConverterStreamT< T >, ChannelFormatConverterStream, NumberFormatConverterStreamT< TFrom, TTo >, NumberFormatConverterStream, CatStream, QueueStream< T >, QueueStream< uint8_t >, DynamicMemoryStream, FadeStream, FrequencyDetectorAutoCorrelation, FrequencyDetectorZeroCrossing, Pipeline, Pipeline::ModifyingStreamAdapter, VolumeStream, FileLoopT< FileType >, FileLoopT< File >, AudioBLEClient, AudioBLEClient, AudioBLEServer, and AudioBLEServer.

◆ availableForWrite()

virtual int availableForWrite ( )

inlineoverridevirtualinherited

Reimplemented from Print.

Reimplemented in AudioLoRa, UDPStream, VBANStream, AudioStreamWrapper, ConverterStream< T >, LoRaStream, EncodedAudioStream, FaustStream< DSP >, AudioFFTBase, I2SCodecStream, MiniAudioStream, StdioStream, A2DPStream, ESPNowStream, HammingFEC< bytecount, block_t >, AbstractURLStream, URLStreamESP32, ReedSolomonFEC< bytecount, additional_bytes >, AnalogAudioArduino, AnalogAudioStream, AudioEffectStreamT< T >, Equalizer3Bands, Equalizer3BandsPerChannel, I2SStream, ReformatBaseStream, TimedStream, MemoryStream, RingBufferStream, MeasuringStream, ProgressStream, Throttle, FilteredStream< T, TF >, FilteredStream< int16_t, int16_t >, ChannelFormatConverterStreamT< T >, ChannelFormatConverterStream, NumberFormatConverterStreamT< TFrom, TTo >, NumberFormatConverterStream, QueueStream< T >, QueueStream< uint8_t >, DynamicMemoryStream, FadeStream, FrequencyDetectorAutoCorrelation, FrequencyDetectorZeroCrossing, Pipeline, VolumeStream, AudioBLEClient, AudioBLEClient, AudioBLEServer, and AudioBLEServer.

◆ begin()

virtual bool begin ( )

inlinevirtualinherited

Reimplemented in AudioOutputWithCallback, AudioMP34DT05, I2SCodecStream, MozziStream, PureDataStream, SPDIFOutput, VS1053Stream, WM8960Stream, AdaptiveResamplingStream, AudioLoRa, ESPNowStream, VBANStream, AudioEffectStreamT< T >, Equalizer3Bands, Equalizer3BandsPerChannel, I2SStream, AudioStreamWrapper, TimerCallbackAudioStream, FrequencyDetectorAutoCorrelation, GoertzelStream, ResampleStreamT< TInterpolator >, FileLoopT< FileType >, FileLoopT< File >, LoRaStream, EncodedAudioStream, AudioBoardStream, AudioFFTBase, AudioKitStream, MiniAudioStream, PortAudioStream, StdioStream, HLSStreamT< URLStream >, AnalogAudioArduino, AnalogAudioStream, AdapterAudioOutputToAudioStream, TimedStream, MemoryStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, MeasuringStream, ProgressStream, Throttle, InputMerge< T >, CallbackStream, FilteredStream< T, TF >, FilteredStream< int16_t, int16_t >, VolumeMeter, AudioInputMonitor, ChannelFormatConverterStreamT< T >, ChannelFormatConverterStream, NumberFormatConverterStreamT< TFrom, TTo >, NumberFormatConverterStream, FormatConverterStream, CatStream, QueueStream< T >, QueueStream< uint8_t >, DynamicMemoryStream, Pipeline, Pipeline::ModifyingStreamAdapter, ResampleStream, VolumeStream, and EqualizerNBands< SampleT, AccT, NUM_TAPS, NUM_BANDS >.

◆ clearNotifyAudioChange()

virtual void clearNotifyAudioChange ( )

inlinevirtualinherited

Deletes all change notify subscriptions.

Reimplemented in RTSPClient< TcpClient, UdpSocket >.

◆ end()

virtual void end ( )

inlinevirtualinherited

Reimplemented in FaustStream< DSP >, AudioMP34DT05, I2SCodecStream, MozziStream, PureDataStream, SPDIFOutput, VS1053Stream, WM8960Stream, AdaptiveResamplingStream, AudioLoRa, ESPNowStream, BufferedTaskStream, URLStreamBufferedT< T >, URLStreamBufferedT< ICYStream >, Equalizer3Bands, I2SStream, AudioStreamWrapper, TimerCallbackAudioStream, FormatConverterStream, GoertzelStream, FileLoopT< FileType >, FileLoopT< File >, EqualizerNBands< SampleT, AccT, NUM_TAPS, NUM_BANDS >, LoRaStream, EncodedAudioStream, AudioFFTBase, AudioKitStream, MiniAudioStream, PortAudioStream, StdioStream, A2DPStream, HLSStreamT< URLStream >, HttpRequest, ICYStreamT< T >, URLStream, URLStreamESP32, AnalogAudioArduino, AnalogAudioStream, AudioEffectStreamT< T >, Equalizer3BandsPerChannel, ReformatBaseStream, AdapterAudioOutputToAudioStream, MemoryStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, InputMixer< T >, InputMerge< T >, CallbackStream, FilteredStream< T, TF >, FilteredStream< int16_t, int16_t >, ChannelFormatConverterStream, NumberFormatConverterStream, CatStream, QueueStream< T >, QueueStream< uint8_t >, DynamicMemoryStream, Pipeline, Pipeline::ModifyingStreamAdapter, VolumeStream, AudioBLEClient, AudioBLEClient, AudioBLEServer, AudioBLEServer, AbstractURLStream, and AudioBLEStream.

◆ flush()

virtual void flush ( )

inlineoverridevirtualinherited

Reimplemented from Print.

Reimplemented in PureDataStream, URLStreamBufferedT< T >, URLStreamBufferedT< ICYStream >, AudioStreamWrapper, ResampleStream, URLStream, BufferedTaskStream, I2SStream, MemoryStream, RingBufferStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, and BufferedStream.

◆ isNotifyActive()

bool isNotifyActive ( )

inlineinherited

Checks if the automatic AudioInfo update is active.

◆ not_supported()

virtual int not_supported	(	int	out,
		const char *	msg = `""`
	)

inlineprotectedvirtualinherited

◆ notifyAudioChange()

void notifyAudioChange ( AudioInfo info )

inlineprotectedinherited

◆ operator bool()

virtual operator bool ( )

inlinevirtualinherited

Reimplemented in A2DPStream, ICYStreamT< T >, AudioBLEStream, AudioFFTBase, PortAudioStream, URLStream, I2SStream, AdapterAudioOutputToAudioStream, TimedStream, MemoryStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, and Pipeline.

◆ readBytes()

virtual size_t readBytes	(	uint8_t *	data,
		size_t	len
	)

inlineoverridevirtualinherited

Implements BaseStream.

Reimplemented in LMSEchoCancellationStream< T >, MDFEchoCancellationStream< Allocator >, MozziStream, PureDataStream, AudioLoRa, URLStreamBufferedT< T >, URLStreamBufferedT< ICYStream >, AudioStreamWrapper, LoRaStream, EncodedAudioStream, FaustStream< DSP >, AudioFFTBase, AudioKitStream, AudioMP34DT05, I2SCodecStream, MiniAudioStream, PortAudioStream, TfLiteAudioStream, A2DPStream, AdaptiveResamplingStream, HLSStreamT< URLStream >, ICYStreamT< T >, URLStream, BufferedTaskStream, URLStreamESP32, VBANStream, AnalogAudioArduino, AnalogAudioStream, AudioEffectStreamT< T >, Equalizer3Bands, Equalizer3BandsPerChannel, I2SStream, ReformatBaseStream, TimedStream, MemoryStream, RingBufferStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, BufferedStream, ConverterStream< T >, MeasuringStream, ProgressStream, Throttle, InputMixer< T >, InputMerge< T >, CallbackStream, FilteredStream< T, TF >, FilteredStream< int16_t, int16_t >, VolumeMeter, AudioInputMonitor, ChannelFormatConverterStreamT< T >, ChannelFormatConverterStream, NumberFormatConverterStreamT< TFrom, TTo >, NumberFormatConverterStream, FadeStream, FrequencyDetectorAutoCorrelation, FrequencyDetectorZeroCrossing, GoertzelStream, Pipeline, VolumeStream, AudioBLEClient, AudioBLEClient, AudioBLEServer, AudioBLEServer, EqualizerNBands< SampleT, AccT, NUM_TAPS, NUM_BANDS >, WM8960Stream, AnalogDriverESP32V1::IO16Bit, and AnalogDriverESP32V2::IO16Bit.

◆ readSilence()

virtual size_t readSilence	(	uint8_t *	buffer,
		size_t	length
	)

inlinevirtualinherited

Source to generate silence: just sets the buffer to 0.

◆ refillReadBuffer()

void refillReadBuffer ( )

inlineprotectedinherited

Refill small read buffer (e.g. 8 bytes) to avoid single byte reads when calling read()

◆ removeNotifyAudioChange()

virtual bool removeNotifyAudioChange ( AudioInfoSupport & bi )

inlinevirtualinherited

Removes a target in order not to be notified about audio changes.

Reimplemented in RTSPClient< TcpClient, UdpSocket >.

◆ setAudioInfo()

virtual void setAudioInfo ( AudioInfo info )

inlineoverridevirtualinherited

Defines the input AudioInfo.

Implements AudioInfoSupport.

Reimplemented in VS1053Stream, WM8960Stream, ChannelFormatConverterStreamT< T >, ChannelFormatConverterStream, VolumeStream, MiniAudioStream, PortAudioStream, I2SCodecStream, MozziStream, SPDIFOutput, AudioLoRa, AnalogAudioStream, I2SStream, TimerCallbackAudioStream, AudioBLEStream, LoRaStream, AudioFFTBase, AudioKitStream, VBANStream, AnalogAudioArduino, Equalizer3Bands, Equalizer3BandsPerChannel, AdapterAudioOutputToAudioStream, TimedStream, MeasuringStream, ProgressStream, CallbackStream, VolumeMeter, AudioInputMonitor, FormatConverterStream, FadeStream, GoertzelStream, Pipeline::ModifyingStreamAdapter, MDFEchoCancellationStream< Allocator >, EncodedAudioStream, PureDataStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, NumberFormatConverterStreamT< TFrom, TTo >, NumberFormatConverterStream, Pipeline, ResampleStream, and ResampleStreamT< TInterpolator >.

◆ setNotifyActive()

void setNotifyActive ( bool flag )

inlineinherited

Deactivate/Reactivate automatic AudioInfo updates: (default is active)

◆ setWriteBufferSize()

void setWriteBufferSize ( int size )

inlineinherited

◆ write() [1/2]

virtual size_t write	(	const uint8_t *	data,
		size_t	len
	)

inlineoverridevirtualinherited

Implements BaseStream.

Reimplemented in URLStream, LMSEchoCancellationStream< T >, MDFEchoCancellationStream< Allocator >, AudioBLEServer, ESP3288AudioOutput, I2SCodecStream, MozziStream, PureDataStream, SPDIFOutput, AudioLoRa, I2SStream, AudioStreamWrapper, ConverterStream< T >, LoRaStream, EncodedAudioStream, FaustStream< DSP >, AudioFFTBase, AudioKitStream, MiniAudioStream, PortAudioStream, TfLiteAudioStream, VS1053Stream, A2DPStream, AdaptiveResamplingStream, BufferedTaskStream, URLStreamESP32, VBANStream, AnalogAudioArduino, AnalogAudioStream, AudioEffectStreamT< T >, Equalizer3Bands, Equalizer3BandsPerChannel, AdapterAudioOutputToAudioStream, TimedStream, MemoryStream, RingBufferStream, BufferedStream, MeasuringStream, ProgressStream, Throttle, CallbackStream, FilteredStream< T, TF >, FilteredStream< int16_t, int16_t >, VolumeMeter, AudioInputMonitor, ChannelFormatConverterStreamT< T >, ChannelFormatConverterStream, NumberFormatConverterStreamT< TFrom, TTo >, NumberFormatConverterStream, FormatConverterStream, FadeStream, FrequencyDetectorAutoCorrelation, FrequencyDetectorZeroCrossing, GoertzelStream, Pipeline, Pipeline::ModifyingStreamAdapter, ResampleStream, ResampleStreamT< TInterpolator >, VolumeStream, AudioBLEClient, AudioBLEClient, AudioBLEServer, EqualizerNBands< SampleT, AccT, NUM_TAPS, NUM_BANDS >, TfLiteAudioStreamBase, WM8960Stream, AnalogDriverESP32V1::IO16Bit, and AnalogDriverESP32V2::IO16Bit.

◆ write() [2/2]

virtual size_t write ( uint8_t ch )

inlineoverridevirtualinherited

Reimplemented in MemoryStream, AudioStreamWrapper, BufferedTaskStream, RingBufferStream, BufferedStream, and URLStream.

◆ writeSilence()

virtual void writeSilence ( size_t len )

inlinevirtualinherited

Writes len bytes of silence (=0).

Member Data Documentation

◆ _timeout

int _timeout = 10

protectedinherited

◆ info

AudioInfo info

protectedinherited

◆ is_notify_active

bool is_notify_active = true

protectedinherited

◆ notify_vector

Vector<AudioInfoSupport*> notify_vector

protectedinherited

◆ tmp_in

RingBuffer<uint8_t> tmp_in {0}

protectedinherited

◆ tmp_out

RingBuffer<uint8_t> tmp_out {0}

protectedinherited

◆ write_buffer_size

int write_buffer_size = MAX_SINGLE_CHARS

protectedinherited

The documentation for this class was generated from the following file:

src/AudioTools/Sandbox/STT/MDFEchoCancellation.h

Public Member Functions

Protected Member Functions

Protected Attributes

Detailed Description

Member Function Documentation

◆ addNotifyAudioChange()

◆ audioInfo()

◆ audioInfoOut()

◆ available()

◆ availableForWrite()

◆ begin()

◆ clearNotifyAudioChange()

◆ end()

◆ flush()

◆ isNotifyActive()

◆ not_supported()

◆ notifyAudioChange()

◆ operator bool()

◆ readBytes()

◆ readSilence()

◆ refillReadBuffer()

◆ removeNotifyAudioChange()

◆ setAudioInfo()

◆ setNotifyActive()

◆ setWriteBufferSize()

◆ write() [1/2]

◆ write() [2/2]

◆ writeSilence()

Member Data Documentation

◆ _timeout

◆ info

◆ is_notify_active

◆ notify_vector

◆ tmp_in

◆ tmp_out

◆ write_buffer_size