1# Audio Processing Module (APM) 2 3<?% config.freshness.owner = 'peah' %?> 4<?% config.freshness.reviewed = '2021-04-13' %?> 5 6## Overview 7 8The APM is responsible for applying speech enhancements effects to the 9microphone signal. These effects are required for VoIP calling and some 10examples include echo cancellation (AEC), noise suppression (NS) and 11automatic gain control (AGC). 12 13The API for APM resides in [`/modules/audio_processing/include`][https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/modules/audio_processing/include]. 14APM is created using the [`AudioProcessingBuilder`][https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/modules/audio_processing/include/audio_processing.h] 15builder that allows it to be customized and configured. 16 17Some specific aspects of APM include that: 18* APM is fully thread-safe in that it can be accessed concurrently from 19 different threads. 20* APM handles for any input sample rates < 384 kHz and achieves this by 21 automatic reconfiguration whenever a new sample format is observed. 22* APM handles any number of microphone channels and loudspeaker channels, with 23 the same automatic reconfiguration as for the sample rates. 24 25 26APM can either be used as part of the WebRTC native pipeline, or standalone. 27