Hey, guys.  The NXP (Philips) UCB1400 audio codec the gumstix uses will normally route the mic preamp to BOTH left and right ADC channels if the mic input is selected in software.  This might explain why you are getting the same audio on both channels.  I would guess that you can use the regular audio mixer application in linux to tell the codec to use line-in instead of mic-in.  For more detail see section 9 of the datasheet at http://www.nxp.com/acrobat_download/datasheets/UCB1400-02.pdf


Remember, if you select line-in you will probably get two channels, but the codec’s analog microphone pre-amplification circuitry will be switched out of the signal path, so you will likely get EXTREMELY low level, possibly distorted sound (or quite likely nothing at all) from a microphone, unless you use an external preamp.  This has nothing to do with gumstix, but would be the same for any PC sound card.


Good luck,

Christopher Whitt

Project Engineer


JASCO Research Limited

Halifax NS Canada B3A 3J6

(902)405-3336 x1008

(902)405-3337 fax

From: gumstix-users-bounces@lists.sourceforge.net [mailto:gumstix-users-bounces@lists.sourceforge.net] On Behalf Of Joey Degges
Sent: Wednesday, March 14, 2007 22:14
To: General mailing list for gumstix users.
Subject: Re: [Gumstix-users] Audio Application



I have actually been testing stereo recording more in depth lately and I have noticed something similar to what you are describing. I have 3 different stereo splitters, but I only know the sepcs on one of them.

Two of the three get no data when either both left and right mics are plugged in, or when just the left or the right is plugged in. But with the third splitter I get two channels, both with the exact same data. I think it may be able to record in stereo but maybe the wiring of the splitter/mics is faulty. >From what I gather it merges all data from the left channel with all data from the right channel resulting in two channels, each filled with both left AND right data.

Sorry if that is a little confusing.

For example I said "testing one two three" into the left mic, and "testing 10 9 8" into the right mic. When I put the resulting file through audacity I found that there are two channels, but each contains "testing one two three testing 10 9 8".

Again this phenomena only happens with one of the three splitters I have, with the other two I get no data whatsoever. Maybe the port is not supplying enough power to power both mics? Maybe the wiring of my mics is bad? Maybe the wiring inside the splitter is bad? Maybe the gumstix audio in jack does something weird with the channels? Maybe it even has to do with the way brec records audio?

That configuration you have does look similar to what I have except I don't use the python package.