EchoCancellation< T > Class Template Reference

Echo cancellation with adaptive LMS filtering for microcontrollers. More...

#include <EchoCancellation.h>

Inheritance diagram for EchoCancellation< T >:

Public Member Functions
	EchoCancellation (Stream &in, size_t lag_samples=0, size_t buffer_size=512, size_t filter_len=32, float mu=0.001f)
	Constructor.
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 ()
virtual void	clearNotifyAudioChange ()
	Deletes all change notify subscriptions.
virtual void	end ()
virtual void	flush () override
bool	isNotifyActive ()
	Checks if the automatic AudioInfo update is active.
virtual	operator bool ()
size_t	readBytes (uint8_t *buf, size_t len) override
	Read input and remove echo (subtract output signal with lag)
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 ()
	Reset the internal buffer and lag state.
virtual void	setAudioInfo (AudioInfo newInfo) override
	Defines the input AudioInfo.
void	setFilterLen (size_t len)
	Set the filter length for the adaptive filter.
void	setLag (size_t lag_samples)
	Set the lag (delay) in samples for echo cancellation.
void	setMu (float mu)
	Set the adaptation rate (mu) for the LMS algorithm.
void	setNotifyActive (bool flag)
	Deactivate/Reactivate automatic AudioInfo updates: (default is active)
void	setWriteBufferSize (int size)
size_t	write (const uint8_t *buf, size_t len) override
	Store the output signal (sent to speaker)
virtual size_t	write (uint8_t ch) override
virtual void	writeSilence (size_t len)
	Writes len bytes of silence (=0).

Protected Member Functions
virtual int	not_supported (int out, const char *msg="")
void	notifyAudioChange (AudioInfo info)
void	refillReadBuffer ()

Protected Attributes
int	_timeout = 10
float	adaptation_rate = 0.01f
size_t	buffer_size
Vector< float >	filter
size_t	filter_len
AudioInfo	info
bool	is_notify_active = true
size_t	lag
Vector< AudioInfoSupport * >	notify_vector
Stream *	p_io = nullptr
RingBuffer< T >	ring_buffer {0}
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>
class audio_tools::EchoCancellation< T >

Echo cancellation with adaptive LMS filtering for microcontrollers.

This class implements echo cancellation using an adaptive FIR filter (LMS algorithm). It estimates the echo path and subtracts the estimated echo from the microphone input.

Constructor & Destructor Documentation

EchoCancellation()

template<typename T = int16_t>

EchoCancellation ( Stream &  in, size_t  lag_samples = 0, size_t  buffer_size = 512, size_t  filter_len = 32, float  mu = 0.001f  )

inline

Constructor.

Parameters

in	Reference to the input stream (microphone or audio input)
lag_samples	Number of samples to delay the echo subtraction (default: 0)
buffer_size	Size of the internal ring buffer (default: 512)

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, AudioFFTBase, I2SCodecStream, TfLiteAudioStream, A2DPStream, HLSStreamT< URLStream >, ICYStreamT< T >, BufferedTaskStream, UDPStream, Equalizer3Bands, Equalizer3BandsPerChannel, I2SStream, TimedStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, BufferedStream, ConverterStream< T >, InputMerge< T >, FrequencyDetectorAutoCorrelation, FrequencyDetectorZeroCrossing, Pipeline::ModifyingStreamAdapter, and VolumeStream.

availableForWrite()

virtual int availableForWrite ( )

inlineoverridevirtualinherited

Reimplemented from Print.

Reimplemented in UDPStream, AudioFFTBase, I2SCodecStream, A2DPStream, AbstractURLStream, URLStreamESP32, Equalizer3Bands, Equalizer3BandsPerChannel, I2SStream, MeasuringStream, ProgressStream, FrequencyDetectorAutoCorrelation, FrequencyDetectorZeroCrossing, and VolumeStream.

begin()

virtual bool begin ( )

inlinevirtualinherited

Reimplemented in AudioOutputWithCallback, SPDIFOutput, VS1053Stream, WM8960Stream, AdaptiveResamplingStream, ESPNowStream, Equalizer3BandsPerChannel, TimerCallbackAudioStream, FrequencyDetectorAutoCorrelation, GoertzelStream, AudioFFTBase, HLSStreamT< URLStream >, AnalogAudioArduino, AnalogAudioStream, MemoryStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, AudioInputMonitor, FormatConverterStream, QueueStream< T >, QueueStream< uint8_t >, DynamicMemoryStream, and Pipeline.

clearNotifyAudioChange()

virtual void clearNotifyAudioChange ( )

inlinevirtualinherited

Deletes all change notify subscriptions.

Reimplemented in RTSPClient< TcpClient, UdpSocket >.

end()

virtual void end ( )

inlinevirtualinherited

Reimplemented in FaustStream< DSP >, I2SCodecStream, VS1053Stream, WM8960Stream, AdaptiveResamplingStream, ESPNowStream, I2SStream, TimerCallbackAudioStream, GoertzelStream, AudioFFTBase, AudioKitStream, HLSStreamT< URLStream >, HttpRequest, ICYStreamT< T >, AnalogAudioStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, InputMixer< T >, InputMerge< T >, QueueStream< T >, QueueStream< uint8_t >, and Pipeline.

flush()

virtual void flush ( )

inlineoverridevirtualinherited

Reimplemented from Print.

Reimplemented in ResampleStream, BufferedTaskStream, and BufferedStream.

operator bool()

virtual operator bool ( )

inlinevirtualinherited

Reimplemented in A2DPStream, ICYStreamT< T >, I2SStream, MemoryStream, and Pipeline.

readBytes()

template<typename T = int16_t>

size_t readBytes ( uint8_t *  buf, size_t  len  )

inlineoverridevirtual

Read input and remove echo (subtract output signal with lag)

Parameters

buf	Pointer to buffer to store processed input (T*)
len	Number of bytes to read

Returns

Number of bytes read from input

Reimplemented from AudioStream.

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, EncodedAudioStream, PureDataStream, GeneratedSoundStream< T >, GeneratedSoundStream< int16_t >, NumberFormatConverterStreamT< TFrom, TTo >, NumberFormatConverterStream, Pipeline, ResampleStream, and ResampleStreamT< TInterpolator >.

setFilterLen()

template<typename T = int16_t>

void setFilterLen ( size_t  len )

inline

Set the filter length for the adaptive filter.

Parameters

len	Length of the adaptive filter

setLag()

template<typename T = int16_t>

void setLag ( size_t  lag_samples )

inline

Set the lag (delay) in samples for echo cancellation.

Parameters

lag_samples

Number of samples to delay the echo subtraction

setMu()

template<typename T = int16_t>

void setMu ( float  mu )

inline

Set the adaptation rate (mu) for the LMS algorithm.

Parameters

mu	Adaptation rate

write() [1/2]

template<typename T = int16_t>

size_t write ( const uint8_t *  buf, size_t  len  )

inlineoverridevirtual

Store the output signal (sent to speaker)

Parameters

buf	Pointer to PCM data sent to the speaker (T*)
len	Number of bytes in buf

Returns

Number of bytes processed

Reimplemented from AudioStream.

write() [2/2]

virtual size_t write ( uint8_t  ch )

inlineoverridevirtualinherited

Reimplemented in BufferedTaskStream, and BufferedStream.

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

• src/AudioTools/STT/EchoCancellation.h