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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)``
**Definition**
Initialization of VAD handle.
**Parameter**
- vad_mode: operating mode of VAD, VAD_MODE_0 to VAD_MODE_4, larger value indicates more aggressive VAD.
**Return**
Handle to VAD.
- ``vad_state_t vad_process(vad_handle_t inst, int16_t *data, int sample_rate_hz, int one_frame_ms);``
**Definition**
Processing of VAD for one frame.
**Parameter**
- inst: VAD handle.
- data: buffer to save both input and output audio stream.
- sample_rate_hz: The Sampling frequency (Hz) can be 32000, 16000, 8000, default: 16000.
- one_frame_ms: The length of the audio processing can be 10ms, 20ms, 30ms, default: 30.
**Return**
- VAD_SILENCE if no voice
- VAD_SPEECH if voice is detected
- ``void vad_destroy(vad_handle_t inst)``
**Definition**
Destruction of a VAD handle.
**Parameter**
- inst: the VAD handle to be destroyed.
AGC
---
.. _overview-1:
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-1:
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-2:
Overview
~~~~~~~~
AEC suppresses echo of the sound played by the speaker of the board.
.. _api-reference-2:
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-3:
Overview
~~~~~~~~
Single-channel speech enhancement. If multiple mics are available with the board, MASE is recommened for noise suppression.
.. _api-reference-3:
API Reference
~~~~~~~~~~~~~
- ``ns_handle_t ns_pro_create(int frame_length, int mode)``
**Definition**
Creates an instance of the more powerful noise suppression algorithm.
**Parameter**
- frame_length_ms: audio frame length in ms.
- mode: 0: Mild, 1: Medium, 2: Aggressive
**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.