SpeexEchoState: Acoustic echo canceller

Classes
class	SpeexEchoState
Defines
#define	SPEEX_ECHO_GET_FRAME_SIZE   3
#define	SPEEX_ECHO_SET_SAMPLING_RATE   24
#define	SPEEX_ECHO_GET_SAMPLING_RATE   25
Typedefs
typedef SpeexEchoState_	SpeexEchoState
Functions
SpeexEchoState *	speex_echo_state_init (int frame_size, int filter_length)
void	speex_echo_state_destroy (SpeexEchoState *st)
void	speex_echo_cancellation (SpeexEchoState *st, const spx_int16_t *rec, const spx_int16_t *play, spx_int16_t *out)
void	speex_echo_cancel (SpeexEchoState *st, const spx_int16_t *rec, const spx_int16_t *play, spx_int16_t *out, spx_int32_t *Yout)
void	speex_echo_capture (SpeexEchoState *st, const spx_int16_t *rec, spx_int16_t *out)
void	speex_echo_playback (SpeexEchoState *st, const spx_int16_t *play)
void	speex_echo_state_reset (SpeexEchoState *st)
int	speex_echo_ctl (SpeexEchoState *st, int request, void *ptr)

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Detailed Description

This is the acoustic echo canceller module.

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Define Documentation

#define SPEEX_ECHO_GET_FRAME_SIZE   3

Obtain frame size used by the AEC

#define SPEEX_ECHO_GET_SAMPLING_RATE   25

Get sampling rate

#define SPEEX_ECHO_SET_SAMPLING_RATE   24

Set sampling rate

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Typedef Documentation

typedef struct SpeexEchoState_ SpeexEchoState

Internal echo canceller state. Should never be accessed directly.

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Function Documentation

void speex_echo_cancel	(	SpeexEchoState *	st,
		const spx_int16_t *	rec,
		const spx_int16_t *	play,
		spx_int16_t *	out,
		spx_int32_t *	Yout
	)

Performs echo cancellation a frame (deprecated)

void speex_echo_cancellation	(	SpeexEchoState *	st,
		const spx_int16_t *	rec,
		const spx_int16_t *	play,
		spx_int16_t *	out
	)

Performs echo cancellation a frame, based on the audio sent to the speaker (no delay is added to playback ni this form)

Parameters:

	st	Echo canceller state
	rec	signal from the microphone (near end + far end echo)
	play	Signal played to the speaker (received from far end)
	out	Returns near-end signal with echo removed

void speex_echo_capture	(	SpeexEchoState *	st,
		const spx_int16_t *	rec,
		spx_int16_t *	out
	)

Perform echo cancellation using internal playback buffer, which is delayed by two frames to account for the delay introduced by most soundcards (but it could be off!)

Parameters:

	st	Echo canceller state
	rec	signal from the microphone (near end + far end echo)
	out	Returns near-end signal with echo removed

int speex_echo_ctl	(	SpeexEchoState *	st,
		int	request,
		void *	ptr
	)

Used like the ioctl function to control the echo canceller parameters

Parameters:

	st	Echo canceller state
	request	ioctl-type request (one of the SPEEX_ECHO_* macros)
	ptr	Data exchanged to-from function

Returns:

0 if no error, -1 if request in unknown

void speex_echo_playback	(	SpeexEchoState *	st,
		const spx_int16_t *	play
	)

Let the echo canceller know that a frame was just queued to the soundcard

Parameters:

	st	Echo canceller state
	play	Signal played to the speaker (received from far end)

void speex_echo_state_destroy

(

SpeexEchoState *

st

)

Destroys an echo canceller state

Parameters:

st

Echo canceller state

SpeexEchoState* speex_echo_state_init	(	int	frame_size,
		int	filter_length
	)

Creates a new echo canceller state

Parameters:

	frame_size	Number of samples to process at one time (should correspond to 10-20 ms)
	filter_length	Number of samples of echo to cancel (should generally correspond to 100-500 ms)

Returns:

Newly-created echo canceller state

void speex_echo_state_reset

(

SpeexEchoState *

st

)

Reset the echo canceller to its original state

Parameters:

st

Echo canceller state

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