On Sun, Feb 21, 2010 at 09:16:39AM +0100, Jan Stary wrote: > I am recording on a MSI Wind PC running -recent, > using the integrated azalia > > azalia0 at pci0 dev 27 function 0 "Intel 82801GB HD Audio" rev 0x01: apic 1 > int 16 (irq 10) > azalia0: codecs: Realtek ALC888 > audio0 at azalia0 > > Everything I record has a small negative DC offset: > http://stare.cz/~hans/.tmp/mike.wav > > I have tried using both the front and the rear mic-in plug, > carefully muting the one I was not using. No difference. > > I have tried using three different mikes. No difference. > > I have tried using _no_ mike, and recording the "silence" > (with the mic input _not_ muted) - the result is a wave > with an almost constant negative DC ofset, sounding like > white noise: http://stare.cz/~hans/.tmp/nomike.wav > > I have tried recording silence when the mic input is muted. > In this case, silence is recorded, with no DC offset. > > This leads me to think that the problem is not with the mikes, > let alone aucat (which I use to record the sound), but is in > the hardware. Is this right? Is this a problem with voltages? > A problem with my audio chip?
> record.adc-0:1_mute=off > record.adc-0:1=224,224 that is amplifying the input to the ADC considerably. the 0..255 mixer values represet -16.5..+30dB *for this codec*. it would be nice if mixer values corresponded to decibles somehow, but that is not the case currently. > inputs.mic=85,85 this is the mic pre-amp. *for this codec*, the values are 0, 10, 20, 30 dB. you'll probably have better results using more mic preamp and not amplifying the ADC input signal. > outputs.mic_dir=input-vr100 here you have the mic jack using 100% AVDD (5.0V). unlikely to change anything, but you might want to try input-vr50 and input-vr80. -- [email protected] SDF Public Access UNIX System - http://sdf.lonestar.org
