How to record audio

1 Article purpose[edit]

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]

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]

3.1 Audio record from headset microphone input[edit]

3.1.1 Record from ALSA device[edit]

Start audio record from 'record_codec' ALSA device:

Info.png 'record_codec' is an alias defined in /etc/asound.conf, for headset microphone input device.
Board $> arecord -D record_codec -f S16_LE -d 10 /tmp/rec.wav

3.1.2 Record via PulseAudio[edit]

3.1.2.1 For ecosystem release ≥ v1.2.0 More info.png[edit]
  • Configure Pulseaudio :

Change Pulseaudio default input source to 'analog_input':

Info.png The Pulseaudio analog_input is defined in /etc/pulse/system.pa configuration file.
Board $> pacmd set-default-source analog_input
  • Start audio record :
Info.png The Pulseaudio device is the default one, so "-D pulse" option can be omitted in the record command.
Board $> arecord -d 10 /tmp/rec.wav
3.1.2.2 For ecosystem release ≤ v1.1.0 More info.png[edit]
  • Configure Pulseaudio :

Change Pulseaudio active profile of the sound card, to 'analog-stereo' profile:

Info.png Example below is given for sound card index 0. Check sound cards index with "pactl list cards short" command.
Board $> pacmd set-card-profile 0 output:analog-stereo+input:analog-stereo
  • Start audio record :
Info.png The Pulseaudio device is the default one, so "-D pulse" option can be omitted in the record command.
Board $> arecord -d 10 /tmp/rec.wav

3.2 Audio record from digital microphone input[edit]

Warning.png The support of digital microphone input is board dependent. Please, check available inputs with "arecord -l" command.

3.2.1 Record from ALSA device[edit]

Start mono audio record from 'record_dfsdm0' ALSA device:

Info.png 'record_dfsdm0' is an alias defined in /etc/asound.conf, for digital microphone U1 input device.
Board $> 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]

Start stereo audio record from 'multi' ALSA device:

Info.png 'multi' device, based on ALSA multi plugin[1], has to be defined in /etc/asound.conf file.
Board $> arecord -D multi -r 16000 -f S32_LE -c 2 -d 10 /tmp/rec.wav

3.2.3 Record via PulseAudio[edit]

The record via Pulseaudio is only available for ecosystem release ≥ v1.2.0 More info.png.

  • Configure Pulseaudio

Change Pulseaudio default input source to 'dmic1_input':

Info.png The Pulseaudio dmic1_input is defined in /etc/pulse/system.pa configuration file.
Board $> pacmd set-default-source dmic1_input
  • Start audio record :
Info.png The Pulseaudio device is the default one, so "-D pulse" option can be omitted in the record command.
Board $> arecord -r 48000 -f S32_LE -c 2 -d 10 /tmp/rec.wav

3.3 Audio record from S/PDIF input[edit]

Warning.png The support of S/PDIF input is board dependent. Please, check available inputs with "arecord -l" command.

3.3.1 Record from ALSA device[edit]

Start audio record from 'record_spdif' ALSA device:

Info.png 'record_spdif' is an alias defined in /etc/asound.conf, for S/PDIF input device.
Info.png A S/PDIF signal must be available on S/PDIF RCA input connector before starting the record command. The record rate must be set according to S/PDIF signal sampling rate.
Board $> arecord -D record_spdif -f S32_LE -c 2 -r 48000 -d 10 /tmp/rec.wav

3.3.2 Record via PulseAudio[edit]

The record via Pulseaudio is only available for ecosystem release ≥ v1.2.0 More info.png.

  • Configure Pulseaudio

Change Pulseaudio default input source to 'iec958_input':

Info.png The Pulseaudio iec958_input is defined in /etc/pulse/system.pa configuration file.
Board $> pacmd set-default-source iec958_input
  • Start audio record :
Info.png The Pulseaudio device is the default one, so "-D pulse" option can be omitted in the record command.
Board $> arecord -r 48000 -f S32_LE -c 2 -d 10 /tmp/rec.wav

4 References[edit]



Attachments

Discussions