Recording with SB16?

I have a SB16 (non Vibra) card that I yesterday attempted to record with, both through the mike and line input, using wavrec/wavplay and sox (with the rec and play frontends).

I could get some faint recording through the mike input, but I wasn't able to get anything properly through the line input, even though the sound from there would go clearly to the speakers connected to the speaker output.

Running sox with the 'stat' option sowed that there was no input and that volume would have to be set to 'inf'. Putting the line signal I had through the mike (disconnecting the speakers first :-) gave a very faint, but also very distorted recording. Using sox with 'stat' this time said the volume would have to be set to 14, which I did. A lot of distortion as I would have expected.

It therefore looks like something is not right, but I can't figure out what? I just want something as simple as possible to record from the mike and line inputs, preferably being able to mix the two.

I'm using linux-2.3.99-pre3, but also tried it with 2.3.33 that was at hand, with the same result. Otherwise it is an almost stock Slackware 7.0 on a P133.

Thanks for any input,

Peter

[quoted lines by Peter Leif Rasmussen on April 3, 2000, at 10:49]

You need to configure your mixdr properly. To do this, use the "aumix" command. Do "aumix -q" to see what your current settings are. It should look something like this:

aumix -q
vol 78, 80
bass 50, 50
treble 50, 50
synth 75, 75, P
pcm 75, 75
speaker 0, 0
line 75, 75, R
mic 0, 0, R
cd 85, 85, P
mix 0, 0
igain 75, 75
ogain 75, 75

These happen to be my mixer settings at this very moment. You'll notice that each line has either three or four columns. The first column is the name of the setting which its line describes. You may have a different set of names than I do, as "aumix" only shows those settings which your sound card actually supports.

The second column is the left channel percentage, and the third column is the right channel percentage. You can see from the above, for example, that my main output volume is ever-so-slightly balanced toward the right because its left channel percentage is 78 whereas its right channel percentage is 80. To change the volume to 90%, for example, issue the command "aumix -v 90".

Some of the lines have a fourth column which is either P (play) or R (record). These are the mixer inputs, and the ones without this column are the mixer outputs. If a mixer input is set to P, then you'll be able to hear it through your speakers, but you'll be unable to record from it by reading from either /dev/dsp or /dev/audio. If you would like to record from it, then you'll have to change its setting to R. To change the CD mixer input from play to record, for example, issue the command "aumix -c R" (note that the R is uppercase). To change it back to play, issue the command "aumix -c P".

To summarize: Make sure that the mixer inputs from which you would like to record are not only set to a high enough percentage, but also set to R (record). If you would like to listen to a mixer input while you're recording, but would not like it to get recorded, then make sure that it's set to P (play).

The default setting for sound card I/O is 8-bits, and, since this does not offer very much granularity, this usually results in a very noticeable amount of background distortion. When the mixer input level is very low, the sound that you're trying to record tends to get burried in the distortion. Increasing the mixer input level will go a long way to overcoming this probem, but it will not eliminate it. The way to get rid of all of the distortion is to tell your recording application to use 16-bit samples.

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sox rec and play seem to introduce lots of noise under the best of circumstances; without changing any wiring or mixer settings I get much better quality from brec/bplay (which uses sys V ipc and multiple processes do simultaneous write between audio device and memory and between memory and disk). brec/bplay is old, apparently unmaintained, and buggy (not all the options work as expected, or indeed at all, for raw sound data for example) but quite functional. In addition, there is a relatively new package call yarec (yet another recorder) which seems to be trying to pick up where brec left off, though it omits some (theoreticly useful) bplay options. I myselft will soon be putting out an alpha release of a program I intend to call rawrec, which will only deal in raw audio, but with many options to control recording, if by any chance you would like to take a look at it I could send it to you.

Britton Kerin
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