esp-sr/acoustic_algorithm

Acoustic Algorithm Introduction

Acoustic algorithms provided in esp-sr include voice activity detection (VAD), adaptive gain control (AGC), acoustic echo cancellation (AEC), noise suppression (NS), and mic-array speech enhancement (MASE). VAD, AGC, AEC, and NS are supported with either single-mic and multi-mic development board, MASE is supported with multi-mic board only.

VAD

Overview

VAD takes an audio stream as input, and outputs the prediction that a frame of the stream contains audio or not.

API Reference

Header

• esp_vad.h

Function

• vad_handle_t vad_create(vad_mode_t vad_mode, int sample_rate_hz, int one_frame_ms)

  Definition

  Initialization of VAD handle.

  Parameter

  • vad_mode: operating mode of VAD, integer ranging from 1 to 5, larger value indicates more aggressive VAD.
  • sample_rate_hz: audio sampling rate in Hz.
  • one_frame_ms: frame length in ms.

  Return

  Handle to VAD.

• vad_state_t vad_process(vad_handle_t inst, int16_t *data)

  Definition

  Processing of VAD for one frame.

  Parameter

  • inst: VAD handle.
  • data: buffer to save both input and output audio stream.

  Return

  VAD handle.

• void vad_destroy(vad_handle_t inst)

  Definition

  Destruction of a VAD handle.

  Parameter

  • inst: the VAD handle to be destroyed.

AGC

Overview

AGC keeps the volume of audio signal at a stable level to avoid the situation that the signal is so loud that gets clipped or too quiet to trigger the speech recognizer.

API Reference

• void *esp_agc_open(int agc_mode, int sample_rate)

  Definition

  Initialization of AGC handle.

  Parameter

  • agc_mode: operating mode of AGC, 3 to enable AGC and 0 to disable it.
  • sample_rate: sampling rate of audio signal.

  Return

  • AGC handle.

• int esp_agc_process(void *agc_handle, short *in_pcm, short *out_pcm, int frame_size, int sample_rate)

  Definition

  Pocessing of AGC for one frame.

  Parameter

  • agc_handle: AGC handle.
  • in_pcm: input audio stream.
  • out_pcm: output audio stream.
  • frame_size: signal frame length in ms.
  • sample_rate: signal sampling rate in Hz.

  Return

  Return 0 if AGC processing succeeds, -1 if fails; -2 and -3 indicate invalid input of sample_rate and frame_size, respectively.

• void esp_agc_clse(void *agc_handle)

  Definition

  Destruction of an AGC handle.

  Parameter

  • agc_handle: the AGC handle to be destroyed.

AEC

Overview

AEC suppresses echo of the sound played by the speaker of the board.

API Reference

• aec_handle_t aec_create(int sample_rate, int frame_length, int filter_length)

  Definition

  Initialization of AEC handle.

  Parameter

  • sample_rate: audio signal sampling rate.
  • frame_length: audio frame length in ms.
  • filter_length: the length of adaptive filter in AEC.

  Return

  Handle to AEC.

• aec_create_t aec_create_multimic(int sample_rate, int frame_length, int filter_length, int nch)

  Definition

  Initialization of AEC handle.

  Parameter

  • sample_rate: audio signal sampling rate.
  • frame_length: audio frame length in ms.
  • filter_length: the length of adaptive filter in AEC.
  • nch: number of channels of the signal to be processed.

  Return

  Handle to AEC.

• void aec_process(aec_handle_t inst, int16_t *indata, int16_t *refdata, int16_t *outdata)

  Definition

  Processing of AEC for one frame.

  Parameter

  • inst: AEC handle.
  • indata: input audio stream, which could be single- or multi-channel, depending on the channel number defined on initialization.
  • refdata: reference signal to be cancelled from the input.
  • outdata: output audio stream, the number of channels is the same as indata.

• void aec_destroy(aec_handle_t inst)

  Definition

  Destruction of an AEC handle.

  Parameter

  • inst: the AEC handle to be destroyed.

NS

Overview

Single-channel speech enhancement. If multiple mics are available with the board, MASE is recommened for noise suppression.

API Reference

• ns_handle_t ns_create(int frame_length_ms)

  Definition

  Initialization of NS handle.

  Parameter

  • frame_length_ms: audio frame length in ms.

  Return

  Handle to NS.

• void ns_process(ns_handle_t inst, int16_t *indata, int16_t *outdata)

  Definition

  Prodessing of NS for one frame.

  Parameter

  • inst: NS handle.
  • indata: input audio stream.
  • outdata: output audio stream.

• void ns_destroy(ns_handle_t inst)

  Definition

  Destruction of a NS handle.

  Parameter

  • inst: the NS handle to be destroyed.

MASE

Overview

Multi-channel speech enhancement. Currently, 2-mic linear array and 3-mic circular array are supported.

API Reference

• mase_handle_t mase_create(int sample_rate, int frame_size, int array_type, float mic_distance, int operating_mode, int filter_strength)

  Definition

  Initialization of MASE handle.

  Parameter

  • sample_rate: signal sampling rate in Hz.
  • frame_size: signal frame length in ms.
  • array_type: 0 for 2-mic linear array and 1 for 3-mic circular array.
  • mic_distance: distance between two microphones in mm.
  • operating_mode: 0 for normal mode and 1 for wake-up enhanced mode.
  • filter_strength: strength of the mic-array speech enhancement, must be 0, 1, 2 or 3 (smaller number indicates better performance and larger hardware cost).
  • aec_on: true to enable and false to disable AEC.
  • filter_length: the length of adaptive filter in AEC.

  Return

  Handle to MASE.

• void mase_process(mase_handle_t st, int16_t *in, int16_t *dsp_out)

  Definition

  Processing of MASE for one frame.

  Parameter

  • st: MASE handle.
  • in: input multi-channel audio stream.
  • dsp_out: output single-channel audio stream.

• void mase_destory(mase_handle_t st)

  Definition

  Destruction of a MASE handle.

  Parameter

  • inst: the MASE handle to be destroyed.