Problems recording sound in FreeBSD 5.1

[Stuart Barkley]

On Mon, 14 Jul 2003 at 22:52 +0200, Joachim Strömbergson wrote:

> Hardware wise, I've got an Asus A7V8X motherboard with built in AC97
> sound. I'm running FreeBSD 5.1 and KDE3.
>
> Is there ar simple way to directly verify that the mic input works?
> Has anybody experienced similar problems? Anybody knows what might
> be the problem?

You should be able to bring up the microphone volume in the mixer and
hear it in your speakers or headphones:

    % mixer mic 100
    Setting the mixer mic to 100:100.
    %

For recording from the microphone, I normally select the recording
source with mixer and set the record level with the rec device:

    % mixer =rec mic mic 100
    Setting the mixer mic to 100:100.
    Recording source: mic
    %

As a test you can copy from /dev/audio to a file and vice-versa for
playback:

    % cp /dev/audio test.au
    ^C [after several seconds of recording]
    % cp test.au /dev/audio
    %

Are you sure you are going into a microphone input and not a line-in
input?  If you have a line-in input, are you able to record from that
input when feeding it a signal from a cd player or something similar?

Are you sure you are going into an input and not an output?  I've seen
some newer motherboards replace the line-in and microphone in jacks
with output jacks for 5.1 sound systems.

Two other things come to mind for AC97 recording:

- AC97 specifies a control register bit which enables a 20dB
microphone input gain.  For the microphones I use, I seem to always
need the boost.  I apply the following patch (to 4.7, I'm not sure if
it applies to 5.1 at all).

--- ../src_dist/sys/dev/sound/pcm/ac97.c        Mon Aug 26 20:25:55 2002
+++ ./sys/dev/sound/pcm/ac97.c  Tue Jan  7 20:47:36 2003
@@ -332,6 +332,12 @@
                                int cur = rdcd(codec, e->reg);
                                val |= cur & ~(max << e->ofs);
                        }
+                       /* stuartb: Enable 20dB mic channel gain boost */
+                       /* TODO: Add ioctl or something else to control this */
+                       /* Do ALL AC97 chips support this? */
+                       if (channel == SOUND_MIXER_MIC)
+                               val |= 0x40;
+
                }
                if (left == 0 && right == 0 && e->mute == 1)
                        val = AC97_MUTE;

- The AC97 specification also has support for an alternate mic input.
I think this controls selection between a front panel and a rear panel
microphone jack.  You might need to set bit 0x0100 (MS) in the General
Purpose Register 0x20.  I have not created a patch for this function.

If you have Windows XP or similar running on your system you can see
these options as advanced setting on the microphone channel.