On Feb 21 16:09:18, Alexandre Ratchov wrote: > 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? > > > > this could be caused by other sources (cd, pc-speaker, > etc). Try muting as much mixer sources as possible.
Everything besides the 'mic' that does the recording is muted. Please see the output of mixerctl attached to the OP. > this could also be caused by the way the codec is wired to > the preamp and/or the power supply. Is there a way I can find out whether this is the case? > Is this a laptop? If so > you could check whether the DC bias is still there when the > A/C adapter is not plugged. It's a MSI Wind PC, which is a 'mini' PC powered by an A/C adapter. It cannot run without it ...
