Audio cards

[Andre Kesteloot]

-------- Original Message --------
Subject: LF: Re: Audio problem
Date: Tue, 24 Dec 2002 09:10:41 +1300
From: "Vernall" <vernall@xtra.co.nz>
Reply-To: rsgb_lf_group@blacksheep.org
To: <rsgb_lf_group@blacksheep.org>
References: <5.1.0.14.0.20021223135158.00aaf7f0@POP3.freeler.nl>



Dick PA0SE,

It was not until recently that I found out about the extent of "mixer
control" placement(s) in a sound card.  There are analogue and digital
mixers.  The MIC-IN, LINE-IN and CD-IN have inputs split to feed an A/D
converter as well as an anlogue mixer going to the master volume control
and LINE-OUT (also an internal power amplifier and speaker out on some
sound cards, newer types have speaker matters external to the PC).

The A/D converted data has a source selector switch (A/D or WAVE data)
before reaching the PC bus.  On newer sound cards the bus has an AC97
compliant interface.  The DSP "number crunching" is done by the PC CPU
and processed data then comes back to the sound card (delayed a little),
where a digital mixer selects the source, it then goes through a stereo
D/A converter, and further to the same analogue mixer that handles the
MIC-IN, LINE-IN and CD-IN (the analogue input signals can bypass the
digital processing).

Sound card drivers do not seem to provide user access to all mixers and
switches on a card.  Different application software may include user
input to selections of analogue and digital mixers, or pre-programme
selections.  There is at least one FFT filter programme I have used that
does apply the digitally filtered sound to the analogue output.  On the
other hand, there are other programmes that do just as you
describe, with only analogue going to audio out, presumably because the
digital output is intended to go to the screen.

Some sound cards also have access to tone controls but I have yet to
experience one.  I'm not sure whether tone control is on the input or
output side, as I have seen some "spectrum displays" that seem to have
minor frequency tilt, which it would be nice to correct to "flat" with
tone controls.

I trust my text explanations are useful.  I do not have a block diagram
at hand of a sound card, but if another reader does, and can scan it,
then I'm sure it would be a good way to add to the information.

73, Bob ZL2CA

     ----- Original Message -----
     From: Dick Rollema <mailto:d.w.rollema@freeler.nl>
     To: LF-Group <mailto:rsgb_lf_group@blacksheep.org>
     Cc: Jan Harte <mailto:jan.harte@hccnet.nl> ; Gerrit Jan Huijsman
     <mailto:gj.huijsman@planet.nl>
     Sent: Tuesday, December 24, 2002 2:03 AM
     Subject: LF: Audio problem

     To All from PA0SE

     Some programs, like Spectran, have the possibility to make the
     processed signal heard via the PC speakers.
     But my problem is that the use of  filters provided by the program
     does not make any difference to the audio at all. The spectrum is
     nicely displayed, so there is no problem on that side.

     The same problem exists with other programs that are supposed to
     provide audio filtering via the computer.  What comes out of the PC
     speakers is the signal at the input of the sound card.
     Jan Harte, PA0HRT, experiences the same problem.

     Whatever is done with the volume controls, nothing helps.

     Any suggestions?

     73, Dick, PA0SE