We're trying to use a gumstix/audiostix combo to record arbitrary analog
signals. We have a signal generator output terminated with a 3.5mm mono
jack plugged into the line in input of the audiostix. We were guessing that
the .wav file brec creates is basically the raw input signal; however, the
frequency seems to be off, and seems to be riding a square wave (I am
guessing that this is how it separates the two channels, which are identical
at this point). We have tried recording a sinusoid with brec and replaying
with bplay, and we do hear a tone. Unfortunately we don't know what range
of input voltages it accepts. The Philips UCB1400 datasheet indicates that
some DSP controls can be set. Is there a way to make sure all these DSP
features are off? Is there a way to separate the two channels and dump the
raw signals for each channel to a file?
Any other suggestions?
Using brec to record mono through audiostix has a few glitches. As Thanos
replied, for mono recordings the Right channel is simply copied to the Left,
but the brec code doesn't throw out the redundant samples and records for
half as long as requested. The audio will sound half speed if played back
using bplay because of the incorrect .wav header and redundant sampling.
Modifying brec to fix this would not be too difficult.
Here is a list of aumix controls and their effect with the UCB1400.
Command / UCB1400 Register / Value written
-i 100 -> 0x1c -> 0x0f0f = Max input gain (whether mic or line input) (+21.5
-i 0 -> 0x1c -> 0x8000 = Min input gain (all mute)
-m 100 -> 0x0e -> 0x0040 = Mic preamp enabled (+20 dB)
-m 0 -> 0x0e -> 0x0000 = Mic preamp disabled
-l R -> 0x1a -> 0x0404 = Select line in for recording
(Stereo recording, mic preamp bypassed)
-m R -> 0x1a -> 0x0000 = Select mic in for recording
(Left mono recording, Right channel copied from Left)
-v 0-100 -> Master volume control
I do not think that separate left volume/right volume control (balance) is
possible using aumix without the ncurses interface.
Good luck, Seth
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