1. Article purpose[edit | edit source]
This article explains how to record audio via the kernel ALSA audio framework in Linux® OS context. The examples below, show how to record audio from the different audio hardware interfaces of the STM32MPU boards.
2. Audio record overview[edit | edit source]
The ALSA framework exposes audio devices associated to the board audio hardware interfaces.
The application audio streams are routed by default through the PulseAudio sound server. PulseAudio exposes audio profiles, which are mapped on the ALSA sound card audio devices. The PulseAudio server provides a command line interface to list audio profiles and to select one, in order to record from a specific audio interface.
The audio record examples in following sections are based on ALSA utilities. Some input paths are configured through ALSA controls. These configurations are detailed in sound card configuration article. If an error is issued when running an example, please refer to Audio troubleshooting grid article for debug.
3. Examples[edit | edit source]
3.1. Audio record from headset microphone input[edit | edit source]
3.1.1. Record from ALSA device[edit | edit source]
Start audio record from 'record_codec' ALSA device:
arecord -D record_codec -f S16_LE -d 10 /tmp/rec.wav
3.1.2. Record via PulseAudio[edit | edit source]
- Configure Pulseaudio :
Change Pulseaudio default input source to 'analog_input':
pactl set-default-source analog_input
- Start audio record :
arecord -d 10 /tmp/rec.wav
3.2. Audio record from digital microphone input[edit | edit source]
3.2.1. Record from ALSA device[edit | edit source]
Start mono audio record from 'record_dfsdm0' ALSA device:
arecord -D record_dfsdm0 -r 16000 -f S32_LE -c 1 -d 10 /tmp/rec.wav
3.2.2. Record multiple digital microphones from a virtual ALSA device[edit | edit source]
Start stereo audio record from 'multi' ALSA device:
arecord -D multi -r 16000 -f S32_LE -c 2 -d 10 /tmp/rec.wav
3.2.3. Record via PulseAudio[edit | edit source]
- Configure Pulseaudio
Change Pulseaudio default input source to 'dmic1_input':
pactl set-default-source dmic1_input
- Start audio record :
arecord -r 48000 -f S32_LE -c 2 -d 10 /tmp/rec.wav
3.3. Audio record from S/PDIF input[edit | edit source]
3.3.1. Get IEC958 status bits[edit | edit source]
Some restrictions may apply to IEC958 control, depending on the SPDIFRX device configuration as it is explained in SPDIFRX device tree configuration and SPDIFRX Linux driver articles.
amixer -c STM32MP1EV cget iface=PCM,name='IEC958 Capture Default'
3.3.2. Record from ALSA device[edit | edit source]
Start audio record from 'record_spdif' ALSA device:
arecord -D record_spdif -f S32_LE -c 2 -r 48000 -d 10 /tmp/rec.wav
3.3.3. Record via PulseAudio[edit | edit source]
- Configure Pulseaudio
Change Pulseaudio default input source to 'iec958_input':
pactl set-default-source iec958_input
- Start audio record :
arecord -r 48000 -f S32_LE -c 2 -d 10 /tmp/rec.wav
4. References[edit | edit source]