We have an issue regarding HW-driven max output level of the A5..A7-mic vs max input sensitivity of Wolfson 8753. Anyway this is about some 20dB missmatch, and regarding the amount of noise/distortion the mic introduces by itself this won't spoil our overall signal quality balance. (you might get sth like a 10..14 bit resolution) 8753 has such a low noise floor even at A/D conversion (see datasheet) you won't recognize or notice the problem, as you still get much better than 60dB S/N. Just boost the digital signal to 0dB and everything will be fine. (I apologize for this botch, but it's not really a problem. Builtin mic isn't HiFi anyway, for bootleg record purposes please use a decent stereo mic connected via USB)
And yes, of course you can record from mic by sw. What do you think we designed this device for ;-) ? cheers jOERG Am Mi 14. Januar 2009 schrieb Erland Lewin: > 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. > > Regards, > > Erland > > 2009/1/13 Werner Almesberger <[email protected]> > > > 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 > > > > _______________________________________________ > > hardware mailing list > > [email protected] > > http://lists.openmoko.org/mailman/listinfo/hardware > > >
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