Bying a Freerunner with the "buzz"-fix on it

Joerg Reisenweber joerg at
Wed Apr 15 05:42:06 CEST 2009

Am Mi  15. April 2009 schrieb Rask Ingemann Lambertsen:
> On Sat, Apr 04, 2009 at 02:33:14PM -0700, Steve Mosher wrote:
> > Cédric Berger wrote:
> > > And if it is the buzz fix (by adding the cap) that causes potential
> > > problems... what about the SOP currently applied to freerunners ? They
> > > may be impacted by incorrect ALSA states ?
> >   Yes, that was a concern of mine as well, so this too had to be checked 
> > and verified. The complication being that a reworked A6 can only be 
> > distinguished AFAIK by visual inspection and not by checking a bit in 
> > the hardware.
>    Perhaps you could turn on MICBIAS and measure for how long the current is
> higher than normal as the capacitor charges. See "MICBIAS CURRENT DETECT" in
> the WM8753L manual.

Alas there's no way to read back the results of "MICBIAS CURRENT DETECT", so 
this won't help.
There's a way to detect buzzfix by rapidly switching on and off MICBIAS and 
testing if you "hear" some buzz when recording from builtin mic. Werner has 
created a small program to do the switching job.

Anyway I'm thinking about tackling this issue from a different more radical 
vector: implementing a autocalibration scheme for mic sensitivity. This would 
involve creating a known sound level (e.g. by playback via speaker) and 
checking (and adjusting) the sensitivity of mic according to the audio level 
fed back to the mic. Advantage: independent of device hw revision / hw patch 
level. No need for creation and maintenance of device specific statefiles or 
other config data. Problem: needs check whether it can be done at all.

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