Audio mixer settings for recording with a microphone
freebsd at edvax.de
Sun Nov 24 17:41:57 UTC 2019
Currently I have the following problem: I'd like to record
something to a file using a microphone. I have the following
sound hardware in my el-cheapo home PC:
% dmesg | grep pcm
pcm0: <HDA VIA VT1708_8 PCM #0 Analog> at cad 0 nid 1 on hdac0
pcm1: <HDA VIA VT1708_8 PCM #1 Analog> at cad 0 nid 1 on hdac0
pcm2: <HDA VIA VT1708_8 PCM #2 Digital> at cad 0 nid 1 on hdac0
That is a built-in sound system (located on the mainboard).
% cat /dev/sndstat
FreeBSD Audio Driver (newpcm: 32bit 2009061500/i386)
pcm0: <HDA VIA VT1708_8 PCM #0 Analog> (play/rec) default
pcm1: <HDA VIA VT1708_8 PCM #1 Analog> (rec)
pcm2: <HDA VIA VT1708_8 PCM #2 Digital> (play)
I have one 3.5mm mic input on the rear and one on the front
of the system. The rear one doesn't seem to work at all. The
front one seems to work, but there is more "background noise"
(ca. 1 kHz sawtooth shape + 1 octave higher "beeeeeeeeeeeeep"
kind of sound, which I can hear on the headphones). If I do
record something (I use audacity), the signal level is very
low, and there is more "interference" beep than "used signal".
I can control the noise with the last 5% of the levels using
the "mic", "igain" and "monitor" control, but the anticipated
signal level doesn't really change.
My suspicion: I'm doing something wrong with the mixer, but
I cannot see what it is...
On my old system, I never had such problems - I would simply
attach the microphone, increase "mic" as needed, and I could
use sox's "rec" command to obtain the audio needed. I put a
CMI soundcard (PCI-based) into that system, which FreeBSD did
For testing, I set the mixer as follows (important settings
marked with an arrow):
% mixer -f /dev/mixer0
Mixer vol is currently set to 100:100
Mixer pcm is currently set to 100:100
Mixer line is currently set to 0:0
Mixer mic is currently set to 100:100 <---
Mixer cd is currently set to 0:0
Mixer rec is currently set to 0:0
Mixer igain is currently set to 100:100 <---
Mixer monitor is currently set to 100:100 <---
Recording source: mic <---
% mixer -f /dev/mixer1
Mixer rec is currently set to 100:100
Mixer monitor is currently set to 100:100
Recording source: monitor
% mixer -f /dev/mixer2
Mixer vol is currently set to 0:0
Mixer pcm is currently set to 0:0
It does not work, as described above.
I tried several microphones. Electret microphones don't work
at all. Dynamic microphones do work, but far too low level.
I've checked them with a semi-pro mixer system - the mikes
work just fine, sufficient level. I chose the one with the
"best" signal, RFT DM-2413M.
Do "modern" PCs (this one is older than 10 years!) require
a pre-amplifier for a microphone?
I assume, if I try to connect the mike to the mixer, and the
mixer to the line-in of the PC, it won't work as well... but
that's the next thing I will try, as I can select "line" as
recording inout as well.
Never touch a running system. ;-)
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...
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