audio pain

[bscott at ntisys.com]

On Wed, 14 Aug 2002, at 4:06pm, Matthew S. Sacks wrote:
> The lspci command identifies the Multimedia audio controller as an Intel
> Corp. 82801BA/BAM AC'97 (rev 05) (This may make sense if ADI chip has been
> integrated onto a motherboard made by Intel....)

  FYI:  AC'97 = Audio Codec 1997.  It is an interface standard for cheap
onboard sound.  Basically, it builds part of the sound into the core chipset
of the motherboard, so that the actual sound chip(s) can be simpler/cheaper
to produce.  So, on your PCI bus, you see the AC97 interface of the Intel
chipset, which is then connected to the ADI chip.

> When I try to play audio with the gnome CD player, the player seems to
> think that it is playing - but I cannot hear anything.

  Do you actually get activity from the drive?  Does the light flash?

  You see, there are two general methods of getting audio off a CD using a 
CD-ROM drive.

  The "traditional" way uses the CD-ROM drive like a glorified Discman(TM).  
The laser reads the digital audio stream from the CD, and the drive's
built-in digital-to-analog converter (DAC) turns it into analog audio.  A
two-channel analog audio cable runs from the CD-ROM drive to the sound
card's amplifier/mixer circuitry, and to the speakers.  The CPU and Linux are
not involved (other than sending the "play" command).  In fact, if the
CD-ROM has front panel buttons, you don't even need a working computer --
just a power source.

  The other, newer way is called Digital Audio Extraction, or DAE.  DAE
reads the digital audio stream from the CD, but does not decode it in the
CD-ROM drive.  Instead, it is sent to the host computer as data, like a
software CD's files.  The host CPU is responsible for doing any processing,
and has to send it out a sound card for you to hear music.

  Each method has advantages.  Analog output from the CD-ROM leaves your
CPU, memory, and system bus free to do other things.  DAE lets the computer
add effects, analyze the audio stream for visualizations, and/or store the
audio for later playback without the CD.

  Many "CD player" programs can only handle the analog output method, and I
am pretty sure that is what your computer is using.  There are two likely 
causes of this problem.  One is that the analog audio cable from the CD-ROM 
drive to the sound card was simply never installed.  If that is the case, 
your best bet is likely to just switch to DAE -- more on that below.

  However, the other possibility is equally likely, and easy to check: The
CD audio channel on your sound card may be turned down (or off).  The sound
card has an onboard mixer that can combine digital audio with analog
sources, and each channel has its own volume control.  From the GNOME "foot"
menu, do Programs -> Multimedia -> Audio Mixer, and check the "CD" slider.

> Same thing happens with XMMS.  XMMS load files button does not see any
> files on the CD.

  XMMS's standard "CD Audio Player" plug-in is kind of funky.  It "fakes"  
having the CD mounted, as if the audio tracks were in the filesystem.  I
never really liked it, and have seen it do weird things.  I always use
instead the "AudioCD Reader" plug-in.  It does DAE, along with CDDB lookups,
and generally behaves in a saner fashion.  You can get it from:

	ftp://mud.stack.nl/pub/OuterSpace/willem/

  Yell if you need help installing it; it is pretty easy, but if you've
never built something from source before, it can appear daunting.

> The sndconfig utility identifies the audio card as the Intel 82801, and
> plays an audio clip of a man saying that he pronounces Unix as Linux.

  "Heeelo, my name is Lee-nus Torvahlds, and I pronounce Lee-nooks like
Lee-nooks."  ;-)

> The quality of that sound clip is very poor, but it is coming out of the
> speakers.

  The clip is, while "classic", not of terribly good quality.  See if you
can track down a sound sample you "know" is good (an MP3 or WAV file would
work), and play that.

-- 
Ben Scott <bscott at ntisys.com>
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