Hi Tim -

I've been working a lot with audio on the gumstix boards lately with varying amounts of success. I have used three different board combinations:

1.) Overo + Summit -- In this combination the audio quality is terrible. I don't recommend using the summit board for any kind of significant audio interfacing.
2.) Verdex + GPSstix -- Fantastic audio quality. Measured -90dB noise floor with 0dB of onboard gain. The only prevelent noise seems to be from the RTC.
3.) Verdex + Audiostix II -- Same as GPSstix.

I use line-in to record. Increasing the gain also increases the noise, but the noise floor is still around -70dB. 

I don't have any experience with audio output on the board, since I am remotely recording files to view later. Are you sure most of your sound quality issues aren't from the output hardware?

-Eric



On Tue, Mar 3, 2009 at 1:12 PM, Tim Redfern <gumstix@eclectronics.org> wrote:
Hello,

I've been experimenting with the gumstix audio input with rather mixed results.

I have audiostix II and gpsstix cards on connex & verdex boards. (rev 1171 boards).

With a microphone input I'm getting a colossal buzzing sound. Definately not useable in any way.
If I use a line level input and use aumix to tweak the mic input gain, output level, and the level
of the signal going in, its better but it still seems to suffer from 'processor noise'.

I have read this suggestion from Arlen Raasch:
http://www.nabble.com/Audiostix-II-mic-audio-noisy-td13119577.html

which seems quite difficult: unsoldering the smt resistor between the audio jacks and connecting
3 components in its place, also to a pin on the ucb-1400 chip? (if I've understood it)

Can anyone confirm whether this should be necessary, if I can expect an improvement?

Or has anyone had success with the audio on the Overo? Does it seem more electrically insulated
from the rest of the computer than the audiostix?

I listen to the audio on the iphone and it seems perfect even though it is so near to antennae,
arm processor, rf transmitters.. I wonder how they manage this?

Thanks,

Tim

> Hi List,
>
> I'm working on a PCB for the Overo which will have a built-in microphone.
> Do I need to pre-amplify signals from an electret microphone (such as this
> one
> http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=668-1197-ND)
> or is that taken care of by the TPS65950?
>
> On the Summit schematic, I see the signals feed directly from the audio
> connector to the LINE_IN_LA and LINE_IN_RA pins on the 70-pin connectors.
> As the Overo schematics aren't available, am I safe to assume that the audio
> bias circuitry described in the datasheet is on the Overo itself?
>
> Also, as a side, I'm curious if there are any reasons why I shouldn't be
> able to connect a single cell LiPoly battery directly to the Overo to supply
> power.  The Summit board says explicitly "5.0V ONLY" on the silkscreen, but
> I see no reason why when examining the schematics and TPS65950.  Will this
> work OK?
>
> Thanks in advance!
> Brad


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