Sound card doesn't support format requested using signalgen

Question

I want to generate a PWM signal on Ubuntu. My first try was to use siggen package. Upon launching signalgen I have the following error:

$ signalgen -v sin 120
signalgen  Ver. 2.3.10 (May 2008)   Digital Signal Generator
/dev/dsp : DAC Opened for output
22050 mono, signed 16 bit, little endian, samples/sec.
8192 bytes per DAC buffer.
[signalgen] Invalid argument : Sound card doesn't support format requested.
$ sudo signalgen -v sin 120
signalgen  Ver. 2.3.10 (May 2008)   Digital Signal Generator
[signalgen] Input/output error : /dev/dsp

What is wrong ?

Answer 1

The last Ubuntu release with /dev/dsp support was 10.04. After that support for /dev/dsp was removed.

To still be able to use older software that rely on /dev/dsp there is a compatibility wrapper padsp which redirects sound output meant for dsp to a running pulseaudio server. We may use this wrapper with the following terminology:

padsp [options] APPLICATION [arguments ...]
padsp signalgen -v sin 120

By this we may be able to also play the output of signalgen to our soundcard. The OSS complatibility layer will be installed as a dependency with siggen .

If we do not want to output the sound directly we can use signalgen to directly write a raw audio file to then play this file through ALSA using aplay

signalgen -w filename -t 5 sin 120 & aplay filename

Note that signalgen will exit if filename already existed.

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A better approach to generate waves without the need of a compatibility layer would be applications that are able to directly address ALSA or PuleAudio.

Sox .

Sox will install the command line utility play which will not only play sound files but can also generate audio waveforms and can add effects to them:

play -n synth sine 120.0 gain 0.0