MICBIAS buzz injection

Erland Lewin erland at lewin.nu
Wed Jan 14 10:47:43 CET 2009

If you could record from the microphone by software on the Freerunner, that
would be great.

I would like to see confirmation that speaking at a conversational level to
the microphone will give a nice signal level that fully uses the 16 bit
range, and also show to some extent the degree of noise at the microphone. I
did some recording tests a few months ago, and was never able to get a good
signal level.

Because of the degree of complexity of the audio path (both hardware &
software), I think it would be nice if OpenMoko had such test software to
verify that microphone recording works well, and that the level is ok as
part of your test suite.



2009/1/13 Werner Almesberger <werner at openmoko.org>

> Joerg and I discussed today how to verify that the MICBIAS buzz rework
> was done properly. Joerg had a very interesting idea: by toggling the
> codec's MICBIAS output, we should be able to create noise that would
> vary depending on whether the rework has been done. He asked me to
> adapt one of my I2C-tweaking programs for this purpose.
> Here's a little program that hammers the Wolfson as fast as it can,
> making MICBIAS oscillate at about 50Hz:
> http://svn.openmoko.org/developers/werner/wolfhammer/
> The result looks like this, on a non-reworked A6, measured on the
> codec side of R4305:
> http://people.openmoko.org/werner/a6-nrw.png
> The amplitude seems pretty small (and I have plenty of ambiental
> noise), so I'm not sure if this is good enough. To verify that
> MICBIAS was indeed being toggled, I added a 1k resistor between the
> measurement point to ground (i.e., parallel to R4305 and C4302),
> which yielded this:
> http://people.openmoko.org/werner/a6-nrw-1k.png
> Joerg, I hope this is useful.
> - Werner
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