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. this could also be caused by the way the codec is wired to the preamp and/or the power supply. Is this a laptop? If so you could check whether the DC bias is still there when the A/C adapter is not plugged. -- Alexandre
