Audio CD issue -- most everything but noise ASUS M4A89TD mobo

Gary Aitken freebsd at
Fri Jun 1 19:51:43 UTC 2012

On 05/31/12 16:16, Polytropon wrote:

> Impedance and level mismatch would be the typical reason
> for this. But basically, it's not _much_ worse than using
> an internal analog connection.

Probably ok if you soldered it up so you didn't have the mismatch from crappy high impedance plug-in connections. You don't happen to know if the analog out (back of drive plug, not the headphone jack) impedance and signal level on a cd is close to matching the line-in on a card, do you?  I'm guessing not.  Most likely would smoke the card/mobo.

>>> Okay, this means the mixer doesn't even have a CD audio
>>> mixer channel. If I remember correctly, this channel is
>>> directly associated to the internal audio connector which
>>> is _not_ present in your system.
>> You mean a cd mixer channel for digital audio only shows up
>> if there is a physical analog audio input???
> Oh god, I hope not!

It looks to me like a digital audio channel won't show up under any circumstances;
it will take a second bridge driver designed to eat cd digital audio,
and the overarching sound driver could pick that up.

> I really have no idea how digital audio output is actually
> represented in the mixer. The "mixer" program will allow
> you to manipulate the levels of channels that are reported
> by the mixer driver (which in turn accesses the sound
> hardware); if the "sound card" doesn't report to have
> CD audio, the corresponding item won't be available.
> Additionally, I'm not sure if "forcing" a CD audio
> output (no idea how, maybe by changing the driver's
> source code?) could affect digital CD audio because
> even though they serve the same purpose, they are
> not related "in wires".

>From my (limited) understanding as a result of this discussion, 
it looks to me like freebsd doesn't work with digital cd audio at all.
If there's no general device to pick up digital audio from the cd,
the only way the sound driver could get it would be for a bridge driver,
or the sound driver itself, to pick up the cd digital audio and present it.
It's difficult to believe that a normal sound bridge driver would be reaching out to a different device and doing that.  

As it stands, cd audio seems to work by picking up the analog audio output and converting it.  Which is what you told me in the first place in less detail :-).

Correct me if I'm wrong...

> A possible way would be to use cdparanoia or something
> like that to extract the data digitally, and then play
> it; "then" also means "in a pipe". No real solution,
> I admit.

Thanks, may look into that.

>> %cat /dev/sndstat
>> FreeBSD Audio Driver (newpcm: 64bit 2009061500/amd64)
>> Installed devices:
>> pcm0:<HDA ATI R6xx HDMI PCM #0 HDMI>  (play)
>> pcm1:<HDA Realtek ALC892 PCM #0 Analog>  (play/rec) default
>> pcm2:<HDA Realtek ALC892 PCM #1 Analog>  (play/rec)
>> pcm3:<HDA Realtek ALC892 PCM #2 Digital>  (play)
>> pcm4:<HDA Realtek ALC892 PCM #3 Digital>  (play)
> Do you maybe also have multiple mixer devices associated?
> Check
> 	% ls /dev/mixer*

boatloads... mixer0 thru mixer4
Reading snd_hda I see now where they are coming from.

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