Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!jarthur!nntp-server.caltech.edu!nyet
From: nyet@nntp-server.caltech.edu (n liu)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Question about digitizing sound on SoundBlaster
Message-ID: <1991May17.143321.14985@nntp-server.caltech.edu>
Date: 17 May 91 14:33:21 GMT
References: <1991May16.203132.5771@leland.Stanford.EDU>
Distribution: usa
Organization: California Institute of Technology, Pasadena
Lines: 43

tchuang@leland.Stanford.EDU ( Chuang) writes:

>Hi,

>   I was wondering if anyone knew of an easy way to record
>sound directly from a source (eg. CD player, etc...) instead
>of recording it through a microphone.  I tried to do this once
>(ie. running a patch cord from the CD line out to the
>SoundBlaster's mic input) but the recorded sound was pretty
>muffled (maybe due to impedence matching problems or something).
>Any ideas?

Actually, the impedance doesn't seem to be much of a problem..
The input is just WAY to sensitive for conventional line level signals.
What you're hearing is an excessive amount of clipping. You just need
to turn down the output level a tad.

If you have variable line outs anywhere, turn it down. If you don't, 
a bit more work is required.

Ideally, you could just make a little op-amp circuit with variable gain
(probably .3 is plenty). A simple resistor divider is fine, but the op-amp
method is good for another reason - making it a low pass filter is a
snap, which is perfect for the 11000 kHz max sampling rate. So far i've just
got a simple resistor divider with a 50 kohm pot:

signal ___________
		  \
		  /
		  \<---------------- out
		  /
		  \
__________________/_________________ ground

Use the intro to the parrot program to check the sound level, or ftp dp25.zip
from your favorite site and use its little real time scope thingy.

The op-amp circuit is good for another use too - you can mix channels easily.

Eventually i'll get it built, and if it works ok i'll send you the plans.
But hey, if somebody has come up with something better, let me know..

nye