MDFEchoCancellation< T, SampleType > Class Template Reference

Acoustic echo canceller using MDF algorithm. More...

#include <MDFEchoCancellation.h>

Inheritance diagram for MDFEchoCancellation< T, SampleType >:

Public Types
using	Mem = Word32
using	Num = typename SampleType::float_t
using	State = EchoState< T, SampleType >
using	Word16 = typename SampleType::word16_t
using	Word32 = typename SampleType::word32_t

Public Member Functions
	MDFEchoCancellation (int filterLength, AudioFFTBase &fftDriver, Allocator &alloc=DefaultAllocator)
	MDFEchoCancellation (int filterLength, int nbMic, int nbSpeakers, AudioFFTBase &fftDriver, Allocator &alloc=DefaultAllocator)
	~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 T *rec, const T *play, T *out)
void	capture (const T *rec, 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 ()
State *	getState ()
bool	isNotifyActive ()
	Checks if the automatic AudioInfo update is active.
virtual	operator bool ()
void	playback (const 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 A >
A *	echoAlloc (size_t count)
	Allocate a zero-initialized array of type A using the configured Allocator (see AudioTools/CoreAudio/AudioBasic/Collections/Allocator.h)
void	echoCancellationImpl (State *st, const T *in, const T *far_end, T *out)
	Core echo cancellation implementation.
void	echoFatal (const char *str)
template<typename A >
void	echoFree (A *ptr, size_t count)
	Deallocate an array previously returned by echoAlloc()
State *	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 T *in, Word16 radius, Word16 *out, int len, Mem *mem, int stride)
	Apply DC notch filter to remove DC offset.
void	mdfAdjustProp (const Word32 *W, int N, int M, int P, Word16 *prop)
	Adjust proportional adaptation weights.
Word32	mdfInnerProd (const Word16 *x, const Word16 *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 Word16 *X, Word32 *ps, int N)
	Compute power spectrum from FFT output.
void	powerSpectrumAccum (const Word16 *X, Word32 *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()
T	saturateToSample (Num x) const
	Rounds and saturates a de-emphasized output sample to T's representable range. Replaces the original fixed int16_t-only WORD2INT macro. Uses NumberConverter::minValueT<T>()/maxValueT<T>() (symmetric +-maxValue(bits) – a harmless 1-LSB narrower on the negative side than T's native asymmetric two's-complement minimum, e.g. -32767 vs -32768 for int16_t).
void	spectralMulAccum (const Word16 *X, const Word32 *Y, Word16 *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)
template<typename A >
A	spxSqrt (A x)
void	weightedSpectralMulConj (const Num *w, const Num p, const Word16 *X, const Word16 *Y, Word32 *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
State *	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 T = int16_t, typename SampleType = MDFFloat>
class audio_tools::MDFEchoCancellation< T, SampleType >

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. This is the underlying algorithm used by MDFEchoCancellationStream – use this class directly (via capture()/playback(), or the self-contained cancel()) if you don't want the Stream-based wrapper.

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 (see AudioTools/CoreAudio/AudioBasic/Collections/Allocator.h – e.g. AllocatorPSRAM/AllocatorESP32 to place the (fairly large) echo-state buffers off the default heap)
• Two-path filter for improved double-talk handling
• Multi-channel support (multiple microphones and speakers)

Note

This implementation requires an external FFT driver implementing the AudioFFTBase interface from AudioFFT.h (only AudioRealFFT has been verified – see the Weaknesses note below).

Example usage:

AudioRealFFT fftDriver;
auto cfg = fftDriver.defaultConfig(RXTX_MODE);
cfg.length = 256;           // frame size in samples
cfg.sample_rate = 16000;
fftDriver.begin(cfg);
 
int filterLength = 1024;  // in samples
MDFEchoCancellation<> echo(filterLength, fftDriver);  // MDFFloat, uses DefaultAllocator
echo.playback(speakerFrame);          // frame_size samples
echo.capture(micFrame, outputFrame);  // frame_size samples each

Strengths (see MDFEchoCancellationStream for the fuller writeup):

• Block-frequency-domain adaptation handles much longer echo tails than a time-domain LMS filter (e.g. LMSEchoCancellationStream) at a fraction of the per-tap cost, and the two-path filter gives real protection against double-talk.
• Multi-channel (nbMic x nbSpeakers) support built in.
• Verified to converge strongly on a synthetic attenuated-echo signal, for both numeric backends (see test_mdf_converges<MDFFloat> and test_mdf_converges<MDFFixedPoint> in tests-cmake/stt/stt_test.cpp).
• The numeric representation used for internal arrays/state is a template parameter (

  Template Parameters

  SampleType,MDFFloat

  by default) chosen when you construct the object, e.g. MDFEchoCancellation<int16_t, MDFFixedPoint> – see MDFFloat/MDFFixedPoint's docs above for the tradeoff.

  Weaknesses:
• Only verified with the AudioRealFFT driver; other AudioFFTBase drivers have their own bin-access implementations that have not been audited.
• capture()/playback() must be called with exactly frame_size samples each; ensureInitialized() re-begin()s the FFT driver you pass in at a different size (2x frame_size) on first use, so dedicate that driver instance to this canceller.
• The two-path thresholds/heuristics are unmodified speexdsp defaults, only exercised here against a single synthetic tone with no near-end noise – real acoustic echo is not yet validated.
• This file required extensive bug-fixing (missing forward declarations, word types hardcoded to int16_t/int32_t despite float-only arithmetic, a 0/0 = NaN in the leak estimate, a leftover fixed-point cast that zeroed the adaptive filter's gradient) to reach its current, tested state; treat further changes with real caution and re-run tests-cmake/stt afterwards.

Template Parameters

T	The PCM sample type used by capture()/playback() (e.g. int16_t, int32_t). Defaults to int16_t. Must match the sample type of the audio actually flowing through the canceller – see saturateToSample().
SampleType	MDFFloat (default) or MDFFixedPoint.

Member Typedef Documentation

Mem

template<typename T = int16_t, typename SampleType = MDFFloat>

using Mem = Word32

Num

template<typename T = int16_t, typename SampleType = MDFFloat>

using Num = typename SampleType::float_t

State

template<typename T = int16_t, typename SampleType = MDFFloat>

using State = EchoState<T, SampleType>

Word16

template<typename T = int16_t, typename SampleType = MDFFloat>

using Word16 = typename SampleType::word16_t

Word32

template<typename T = int16_t, typename SampleType = MDFFloat>

using Word32 = typename SampleType::word32_t

Constructor & Destructor Documentation

MDFEchoCancellation() [1/2]

template<typename T = int16_t, typename SampleType = MDFFloat>

MDFEchoCancellation ( int  filterLength, AudioFFTBase &  fftDriver, Allocator &  alloc = DefaultAllocator  )

inline

Initialize echo canceller with single channel (mono)

Parameters

filterLength	Length of echo cancellation filter in samples
fftDriver	FFT driver instance from AudioFFT
alloc	Allocator used for the echo-state buffers (optional, defaults to the shared DefaultAllocator)

MDFEchoCancellation() [2/2]

template<typename T = int16_t, typename SampleType = MDFFloat>

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

inline

Initialize echo canceller with multiple channels

Parameters

filterLength	Length of echo cancellation filter in samples
nbMic	Number of microphone channels
nbSpeakers	Number of speaker channels
fftDriver	FFT driver instance from AudioFFT
alloc	Allocator used for the echo-state buffers (optional, defaults to the shared DefaultAllocator)

~MDFEchoCancellation()

template<typename T = int16_t, typename SampleType = MDFFloat>

~MDFEchoCancellation ( )

inline

Destructor

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 MP3EncoderShine, PureDataStream, PWMAudioOutput< PWMDriverT >, 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, FaustStream< DSP >, AudioMP34DT05, I2SCodecStream, MiniAudioStream, StdioStream, TfLiteAudioStream, A2DPStream, ESPNowStream, HammingFEC< bytecount, block_t >, HLSStreamT< URLStream >, HttpRequest, ICYStreamT< T >, URLStream, BufferedTaskStream, NRF24Stream, ReedSolomonFEC< bytecount, additional_bytes >, SPIAudioSlave, UDPStream, USBAudioDeviceBase, AnalogAudioStream, AudioEffectStreamT< T >, AudioEffectStream, 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, QualityAnalysisStream, VolumeStream, FileLoopT< FileType >, FileLoopT< File >, AudioFFTBase, AudioBLEClient, AudioBLEClient, AudioBLEServer, and AudioBLEServer.

availableForWrite()

virtual int availableForWrite ( )

inlineoverridevirtualinherited

Reimplemented from Print.

Reimplemented in AudioLoRa, UDPStream, VBANStream, AudioStreamWrapper, ConverterStream< T >, EncodedAudioStream, FaustStream< DSP >, I2SCodecStream, MiniAudioStream, StdioStream, A2DPStream, ESPNowStream, HammingFEC< bytecount, block_t >, AbstractURLStream, URLStreamESP32, NRF24Stream, ReedSolomonFEC< bytecount, additional_bytes >, SPIAudioSlave, USBAudioDeviceBase, AnalogAudioStream, AudioEffectStreamT< T >, AudioEffectStream, 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, QualityAnalysisStream, VolumeStream, AudioFFTBase, AudioBLEClient, AudioBLEClient, AudioBLEServer, and AudioBLEServer.

begin()

virtual bool begin ( )

inlinevirtualinherited

Reimplemented in AudioOutputWithCallback, AudioMP34DT05, I2SCodecStream, MozziStream, PureDataStream, SPDIFOutput, VS1053Stream, WM8960Stream, AdaptiveResamplingStream, AudioLoRa, ESPNowStream, USBAudioDeviceBase, VBANStream, AudioEffectStreamT< T >, AudioEffectStream, Equalizer3Bands, Equalizer3BandsPerChannel, I2SStream, AudioStreamWrapper, TimerCallbackAudioStream, FrequencyDetectorAutoCorrelation, GoertzelStream, ResampleStreamT< TInterpolator >, FileLoopT< FileType >, FileLoopT< File >, EncodedAudioStream, AudioBoardStream, AudioKitStream, MiniAudioStream, PortAudioStream, StdioStream, HLSStreamT< URLStream >, NRF24Stream, 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, QualityAnalysisStream, ResampleStream, VolumeStream, AudioFFTBase, and EqualizerNBands< SampleT, AccT, NUM_TAPS, NUM_BANDS >.

cancel()

template<typename T = int16_t, typename SampleType = MDFFloat>

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

inline

Perform echo cancellation

Parameters

rec	Recorded signal (with echo)
play	Playback signal (reference)
out	Output signal (echo removed)

capture()

template<typename T = int16_t, typename SampleType = MDFFloat>

void capture ( const T *  rec, T *  out  )

inline

Process captured audio with buffered playback

Parameters

rec	Recorded signal
out	Output signal (echo removed)

clearNotifyAudioChange()

virtual void clearNotifyAudioChange ( )

inlinevirtualinherited

Deletes all change notify subscriptions.

Reimplemented in RTSPClient< TcpClient, UdpSocket >.

control()

template<typename T = int16_t, typename SampleType = MDFFloat>

int control ( int  request, void *  ptr  )

inline

Control/query echo canceller parameters

Parameters

request	Request type (ECHO_GET_FRAME_SIZE, etc.)
ptr	Pointer to parameter value

Returns

0 on success, -1 on error

echoAlloc()

template<typename T = int16_t, typename SampleType = MDFFloat>

template<typename A >

A * echoAlloc ( size_t  count )

inlineprotected

Allocate a zero-initialized array of type A using the configured Allocator (see AudioTools/CoreAudio/AudioBasic/Collections/Allocator.h)

Template Parameters

A	Type of objects to allocate

Parameters

count

Number of objects to allocate

Returns

Pointer to allocated and zero-initialized memory

echoCancellationImpl()

template<typename T = int16_t, typename SampleType = MDFFloat>

void echoCancellationImpl ( State *  st, const T *  in, const T *  far_end, T *  out  )

inlineprotected

Core echo cancellation implementation.

Implements the complete MDF echo cancellation algorithm including:

• Pre-processing (DC notch filter, pre-emphasis)
• FFT transformation of input signals
• Adaptive filter update in frequency domain
• Echo prediction and subtraction
• Two-path filter switching for double-talk handling
• Post-processing (de-emphasis)

Parameters

st	Echo state structure containing all internal state
in	Input signal from microphones (interleaved if multi-channel)
far_end	Reference signal from speakers (interleaved if multi-channel)
out	Output signal with echo removed (interleaved if multi-channel)

echoFatal()

template<typename T = int16_t, typename SampleType = MDFFloat>

void echoFatal ( const char *  str )

inlineprotected

echoFree()

template<typename T = int16_t, typename SampleType = MDFFloat>

template<typename A >

void echoFree ( A *  ptr, size_t  count  )

inlineprotected

Deallocate an array previously returned by echoAlloc()

Template Parameters

A	Type of objects to deallocate

Parameters

ptr	Pointer to memory to deallocate
count	Number of objects originally allocated (must match the echoAlloc() call that produced ptr)

echoStateInitMc()

template<typename T = int16_t, typename SampleType = MDFFloat>

State * echoStateInitMc ( int  frame_size, int  filter_length, int  nb_mic, int  nb_speakers  )

inlineprotected

Initialize multi-channel echo canceller state.

Parameters

frame_size	Number of samples per frame
filter_length	Total filter length in samples
nb_mic	Number of microphone channels
nb_speakers	Number of speaker channels

Returns

Pointer to initialized echo state, or nullptr on failure

echoWarning()

template<typename T = int16_t, typename SampleType = MDFFloat>

void echoWarning ( const char *  str )

inlineprotected

end()

virtual void end ( )

inlinevirtualinherited

Reimplemented in FaustStream< DSP >, AudioMP34DT05, I2SCodecStream, MozziStream, PureDataStream, SPDIFOutput, VS1053Stream, WM8960Stream, AdaptiveResamplingStream, AudioLoRa, ESPNowStream, BufferedTaskStream, URLStreamBufferedT< T >, URLStreamBufferedT< ICYStream >, USBAudioDeviceBase, Equalizer3Bands, I2SStream, AudioStreamWrapper, TimerCallbackAudioStream, FormatConverterStream, GoertzelStream, FileLoopT< FileType >, FileLoopT< File >, EqualizerNBands< SampleT, AccT, NUM_TAPS, NUM_BANDS >, EncodedAudioStream, AudioKitStream, MiniAudioStream, PortAudioStream, StdioStream, A2DPStream, HLSStreamT< URLStream >, HttpRequest, ICYStreamT< T >, URLStream, URLStreamESP32, NRF24Stream, SPIAudioSlave, AnalogAudioStream, AudioEffectStreamT< T >, AudioEffectStream, Equalizer3BandsPerChannel, ReformatBaseStream, AdapterAudioOutputToAudioStream, MemoryStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, InputMixer< T, SumT >, InputMerge< T >, CallbackStream, FilteredStream< T, TF >, FilteredStream< int16_t, int16_t >, ChannelFormatConverterStream, NumberFormatConverterStream, CatStream, QueueStream< T >, QueueStream< uint8_t >, DynamicMemoryStream, Pipeline, Pipeline::ModifyingStreamAdapter, VolumeStream, AudioFFTBase, AudioBLEClient, AudioBLEClient, AudioBLEServer, AudioBLEServer, AbstractURLStream, and AudioBLEStream.

ensureInitialized()

template<typename T = int16_t, typename SampleType = MDFFloat>

void ensureInitialized ( )

inlineprotected

Ensure echo canceller is initialized (lazy initialization)

filterDcNotch16()

template<typename T = int16_t, typename SampleType = MDFFloat>

void filterDcNotch16 ( const T *  in, Word16  radius, Word16 *  out, int  len, Mem *  mem, int  stride  )

inlineprotected

Apply DC notch filter to remove DC offset.

Parameters

in	Input signal
radius	Filter radius parameter
out	Output filtered signal
len	Length of signal
mem	Filter memory state (2 values)
stride	Stride for accessing input array

flush()

virtual void flush ( )

inlineoverridevirtualinherited

Reimplemented from Print.

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

getFilterLength()

template<typename T = int16_t, typename SampleType = MDFFloat>

int getFilterLength ( )

inline

Get filter length

getFrameSize()

template<typename T = int16_t, typename SampleType = MDFFloat>

int getFrameSize ( )

inline

Get frame size

getImpulseResponse()

template<typename T = int16_t, typename SampleType = MDFFloat>

void getImpulseResponse ( echo_int32_t *  response )

inline

Get impulse response

Parameters

response

Buffer to store impulse response (must be pre-allocated)

getImpulseResponseSize()

template<typename T = int16_t, typename SampleType = MDFFloat>

int getImpulseResponseSize ( )

inline

Get impulse response size

getMicChannels()

template<typename T = int16_t, typename SampleType = MDFFloat>

int getMicChannels ( )

inline

Get number of microphone channels

getSamplingRate()

template<typename T = int16_t, typename SampleType = MDFFloat>

int getSamplingRate ( )

inline

Get sampling rate

getSpeakerChannels()

template<typename T = int16_t, typename SampleType = MDFFloat>

int getSpeakerChannels ( )

inline

Get number of speaker channels

getState()

template<typename T = int16_t, typename SampleType = MDFFloat>

State * getState ( )

inline

Get underlying state (for advanced usage)

isNotifyActive()

bool isNotifyActive ( )

inlineinherited

Checks if the automatic AudioInfo update is active.

mdfAdjustProp()

template<typename T = int16_t, typename SampleType = MDFFloat>

void mdfAdjustProp ( const Word32 *  W, int  N, int  M, int  P, Word16 *  prop  )

inlineprotected

Adjust proportional adaptation weights.

Parameters

W	Filter weights in frequency domain
N	FFT size
M	Number of filter blocks
P	Number of channels
prop	Output proportional weights (normalized)

mdfInnerProd()

template<typename T = int16_t, typename SampleType = MDFFloat>

Word32 mdfInnerProd ( const Word16 *  x, const Word16 *  y, int  len  )

inlineprotected

Compute inner product of two vectors.

Parameters

x	First input vector
y	Second input vector
len	Length of vectors

Returns

Sum of element-wise products

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, PortAudioStream, URLStream, USBAudioDeviceBase, I2SStream, AdapterAudioOutputToAudioStream, TimedStream, MemoryStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, Pipeline, and AudioFFTBase.

playback()

template<typename T = int16_t, typename SampleType = MDFFloat>

void playback ( const T *  play )

inline

Buffer playback signal for later processing

Parameters

play	Playback signal to buffer

powerSpectrum()

template<typename T = int16_t, typename SampleType = MDFFloat>

void powerSpectrum ( const Word16 *  X, Word32 *  ps, int  N  )

inlineprotected

Compute power spectrum from FFT output.

Parameters

X	FFT output in packed format
ps	Output power spectrum
N	FFT size

powerSpectrumAccum()

template<typename T = int16_t, typename SampleType = MDFFloat>

void powerSpectrumAccum ( const Word16 *  X, Word32 *  ps, int  N  )

inlineprotected

Accumulate power spectrum from FFT output.

Parameters

X	FFT output in packed format
ps	Accumulated power spectrum (updated in place)
N	FFT size

readBytes()

virtual size_t readBytes ( uint8_t *  data, size_t  len  )

inlineoverridevirtualinherited

Implements BaseStream.

Reimplemented in LMSEchoCancellationStream< T >, MDFEchoCancellationStream< T, SampleType >, USBAudioDeviceBase, MozziStream, PureDataStream, AudioLoRa, URLStreamBufferedT< T >, URLStreamBufferedT< ICYStream >, AudioStreamWrapper, EncodedAudioStream, FaustStream< DSP >, AudioKitStream, AudioMP34DT05, I2SCodecStream, MiniAudioStream, PortAudioStream, TfLiteAudioStream, A2DPStream, AdaptiveResamplingStream, HLSStreamT< URLStream >, ICYStreamT< T >, URLStream, BufferedTaskStream, URLStreamESP32, NRF24Stream, SPIAudioSlave, VBANStream, AnalogAudioStream, AudioEffectStreamT< T >, AudioEffectStream, Equalizer3Bands, Equalizer3BandsPerChannel, I2SStream, ReformatBaseStream, TimedStream, MemoryStream, RingBufferStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, BufferedStream, ConverterStream< T >, MeasuringStream, ProgressStream, Throttle, InputMixer< T, SumT >, 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, QualityAnalysisStream, VolumeStream, AudioFFTBase, 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 >.

reset()

template<typename T = int16_t, typename SampleType = MDFFloat>

void reset ( )

inline

Reset echo canceller state

saturateToSample()

template<typename T = int16_t, typename SampleType = MDFFloat>

T saturateToSample ( Num  x ) const

inlineprotected

Rounds and saturates a de-emphasized output sample to T's representable range. Replaces the original fixed int16_t-only WORD2INT macro. Uses NumberConverter::minValueT<T>()/maxValueT<T>() (symmetric +-maxValue(bits) – a harmless 1-LSB narrower on the negative side than T's native asymmetric two's-complement minimum, e.g. -32767 vs -32768 for int16_t).

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, MDFEchoCancellationStream< T, SampleType >, AudioKitStream, NRF24Stream, SPIAudioSlave, USBAudioDeviceBase, VBANStream, Equalizer3Bands, Equalizer3BandsPerChannel, AdapterAudioOutputToAudioStream, TimedStream, MeasuringStream, ProgressStream, CallbackStream, VolumeMeter, AudioInputMonitor, FormatConverterStream, FadeStream, GoertzelStream, Pipeline::ModifyingStreamAdapter, QualityAnalysisStream, AudioFFTBase, EncodedAudioStream, PureDataStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, NumberFormatConverterStreamT< TFrom, TTo >, NumberFormatConverterStream, Pipeline, ResampleStream, and ResampleStreamT< TInterpolator >.

setFFTDriver()

template<typename T = int16_t, typename SampleType = MDFFloat>

void setFFTDriver ( AudioFFTBase &  fftDriver )

inline

Set FFT driver (must be called before first use)

Parameters

fftDriver

Reference to FFT driver instance

setFilterLength()

template<typename T = int16_t, typename SampleType = MDFFloat>

void setFilterLength ( int  len )

inline

Set filter length (must be called before first use)

Parameters

len	Length of echo cancellation filter in samples

setMicChannels()

template<typename T = int16_t, typename SampleType = MDFFloat>

void setMicChannels ( int  num )

inline

Set number of microphone channels (must be called before first use)

Parameters

num	Number of microphone channels

setNotifyActive()

void setNotifyActive ( bool  flag )

inlineinherited

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

setSamplingRate()

template<typename T = int16_t, typename SampleType = MDFFloat>

void setSamplingRate ( int  rate )

inline

Set sampling rate

Parameters

rate	Sampling rate in Hz

setSpeakerChannels()

template<typename T = int16_t, typename SampleType = MDFFloat>

void setSpeakerChannels ( int  num )

inline

Set number of speaker channels (must be called before first use)

Parameters

num	Number of speaker channels

setWriteBufferSize()

void setWriteBufferSize ( int  size )

inlineinherited

spectralMulAccum()

template<typename T = int16_t, typename SampleType = MDFFloat>

void spectralMulAccum ( const Word16 *  X, const Word32 *  Y, Word16 *  acc, int  N, int  M  )

inlineprotected

Accumulate spectral multiplication across multiple frames.

Parameters

X	Input spectrum (M frames)
Y	Filter weights in frequency domain
acc	Output accumulated result
N	FFT size
M	Number of frames to accumulate

spxCos()

template<typename T = int16_t, typename SampleType = MDFFloat>

float spxCos ( float  x )

inlineprotected

Compute cosine function.

Parameters

x	Input angle in radians

Returns

Cosine of x

spxExp()

template<typename T = int16_t, typename SampleType = MDFFloat>

float spxExp ( float  x )

inlineprotected

Compute exponential function.

Parameters

x	Input value

Returns

e raised to the power of x

spxIlog2()

template<typename T = int16_t, typename SampleType = MDFFloat>

echo_int16_t spxIlog2 ( echo_uint32_t  x )

inlineprotected

spxSqrt()

template<typename T = int16_t, typename SampleType = MDFFloat>

template<typename A >

A spxSqrt ( A  x )

inlineprotected

weightedSpectralMulConj()

template<typename T = int16_t, typename SampleType = MDFFloat>

void weightedSpectralMulConj ( const Num *  w, const Num  p, const Word16 *  X, const Word16 *  Y, Word32 *  prod, int  N  )

inlineprotected

Compute weighted spectral multiplication with conjugate.

Parameters

w	Weight array for each frequency bin
p	Global scaling factor
X	First input spectrum
Y	Second input spectrum (conjugated)
prod	Output product
N	FFT size

write() [1/2]

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

inlineoverridevirtualinherited

Implements BaseStream.

Reimplemented in URLStream, LMSEchoCancellationStream< T >, MDFEchoCancellationStream< T, SampleType >, AudioBLEServer, ESP3288AudioOutput, I2SCodecStream, MozziStream, PureDataStream, SPDIFOutput, AudioLoRa, USBAudioDeviceBase, I2SStream, AudioStreamWrapper, ConverterStream< T >, EncodedAudioStream, FaustStream< DSP >, AudioKitStream, MiniAudioStream, PortAudioStream, TfLiteAudioStream, VS1053Stream, A2DPStream, AdaptiveResamplingStream, BufferedTaskStream, URLStreamESP32, NRF24Stream, SPIAudioSlave, VBANStream, AnalogAudioStream, AudioEffectStreamT< T >, AudioEffectStream, 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, QualityAnalysisStream, ResampleStream, ResampleStreamT< TInterpolator >, VolumeStream, AudioFFTBase, 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

allocator

template<typename T = int16_t, typename SampleType = MDFFloat>

Allocator& allocator

protected

Allocator used for the echo-state buffers

fft_driver

template<typename T = int16_t, typename SampleType = MDFFloat>

AudioFFTBase* fft_driver

protected

Pointer to FFT driver instance

filter_length

template<typename T = int16_t, typename SampleType = MDFFloat>

int filter_length

protected

Length of echo cancellation filter

info

AudioInfo info

protectedinherited

initialized

template<typename T = int16_t, typename SampleType = MDFFloat>

bool initialized = false

protected

Lazy initialization flag

is_notify_active

bool is_notify_active = true

protectedinherited

nb_mic

template<typename T = int16_t, typename SampleType = MDFFloat>

int nb_mic

protected

Number of microphone channels

nb_speakers

template<typename T = int16_t, typename SampleType = MDFFloat>

int nb_speakers

protected

Number of speaker channels

notify_vector

Vector<AudioInfoSupport*> notify_vector

protectedinherited

state

template<typename T = int16_t, typename SampleType = MDFFloat>

State* state = nullptr

protected

Pointer to internal echo canceller state

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

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

• src/AudioTools/AEC/MDFEchoCancellation.h