[pulseaudio-discuss] PulseAudio and AX25 Soundmodem

Gary Huntress gary.huntress at gmail.com
Sat Sep 26 17:37:51 PDT 2009

I have been trying for some time to get one sound-based application
running.   The application is soundmodem
http://www.baycom.org/~tom/ham/soundmodem/ and is foundational to
linux ax25 and ham radio applications.   Its simplest configuration is
to connect the audio from a ham radio to the mic input.   Soundmodem
will demodulate the binary data from the audio stream.

Soundmodem has been around for many years and is mature and is known
to work on older linux distributions.   I have tried 3 different
laptops with Ubuntu 8 and 9, and Fedora 10 and 11.   I have the same
difficulty on all attempts.   I can hear the audio, I can mix/change
the audio level, and I can display the audio waveform using the built
in oscilloscope.  Occasionally it will detect the carrier but
soundmodem will not decode any audio data.

I have saved a screenshot here http://www.freesql.org/soundmodem.png
and you can see evidence of some kind of digital pulse train that is
corrupting the audio stream.  Could this be a configuration problem
relating to sampling?  I do know that soundmodem uses /dev/dsp and I
start the app using padsp, also it reports that its sampling rate is

Thx for any help or info, I'm really interested in getting this working.

Gary H.

More information about the pulseaudio-discuss mailing list