RE: [Gumstix-users] mono sound, microphone, speech recognition

[Seth C. <se...@ca...>]

Hi Frank,

1. Is there now mono sound available?
I did not find anything on that, except from several people in the
mailing list with the same question. Last time it was asked half a year
ago and not answered. Maybe something has happened since then...

>> I believe Gumstix Craig is working on adding the ALSA drivers to the next
buildroot update. These should have better support for mono and other
features.

2. If there is no mono available, then is there a work-around for
programs using mono sound?

>> A general work-around would require a few changes to the current OSS
drivers. If you just need brec to capture sound, then a couple of changes to
brec.c could fix the file format problem. Currently, brec "mono" recordings
have data repeated at each sample, so the first fix is to throw away every
other data point. The next problem is that it thinks the sampling rate is
double and puts this incorrect value into the .wav header, so playback with
bplay is at the wrong speed. Thus, the second fix is to divide the value
that brec writes to the header by two. Caveat: this is from memory of months
ago, so verify.

3. Is there a speech recognition program already in the gumstix world?
Did anybody work on that?

>> not sure

4. Getting the mic of a "standard" headset working was quite hard.
Finally I got it working with 5V external power and a 2.2 kOhm resistor.
Could someone confirm, that this is the way it should be done?
(Everybody is referring the to the microphone-powering-website, but
there are several wirings and the one exactly below "Other wirings",
leaving the middle line grounded or not connected, did not work.)

>> This is an excellent observation. Most "standard" soundblaster headsets
expect that the bias voltage go to the middle ring of the 3.5mm jack.
However, the Audiostix schematics show that bias voltage is going to the end
conductor, a la the less common "Other wirings" circuit.

>> I wonder is this is a design bug that could be corrected in the next rev
of the board???

>> What happens if you switch the Left and Right contacts of your headset,
say using
	3.5mm female to RCA male connectors --> reverse RCA female connectors to
3.5mm male?
I don't think this would harm anything electrically and may put AudioStix's
bias voltage to where the headset expects it. However, the audiostix VDD
might be noisy similar to your USB experiment. Please let me know if you try
this.

5. Is it normal, that I have to choose the line-in for recording? In the
mailinglist I have seen some people not using the 'aumix -lR' command.
Why does recording with 'aumix -mR' not work, if according to the
mailinglist, the only difference between the mic and line-in is that the
mic reads mono and copies the right channel to the left channel.
Recording from the line-in gives me perfect sound on both speakers.

>> aumix commands just set control bits on sound codecs. For the UCB1400,
the line in and mic in are the same physical plug, so switching from mic to
line doesn't do much other than expect a mono signal vs. stereo. You can
leave it at -lR and one of the channels would just record noise. The +20 dB
preamp can also be activated regardless of line vs. mic input. It's just
that it causes distortion and clipping at line level voltages.

- Seth