[pulseaudio-discuss] PulseAudio and AX25 Soundmodem

Lennart Poettering lennart at poettering.net
Tue Sep 29 00:55:23 PDT 2009

On Sat, 26.09.09 20:37, Gary Huntress (gary.huntress at gmail.com) wrote:

> 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.

Uh, generally I'd suggest using the low-evel ALSA-devices directly for
low-level applications such as soft modems, i.e. bypassing PA.

> 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
> 9600.

I am sorry, but I fear I cannot help you much here. Running a softmoem
via padsp sounds very messy to me though. The software really should be
updated to use the ALSA API. /dev/dsp is not supported anymore in
Fedora 11 and newer, and the interface has been deprecated for 10
years now or so. If your app still uses /dev/dsp someone should coming
out of the rock he has been living under.


Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net
http://0pointer.net/lennart/           GnuPG 0x1A015CC4

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