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: <1991May18.113449.11552@nntp-server.caltech.edu>
Date: 18 May 91 11:34:49 GMT
References: <1991May16.203132.5771@leland.Stanford.EDU> <1991May17.143321.14985@nntp-server.caltech.edu> <1991May17.191012.28047@agate.berkeley.edu>
Distribution: usa
Organization: California Institute of Technology, Pasadena
Lines: 35

jorourke@monsoon.Berkeley.EDU (Jason O'Rourke) writes:

>In article <1991May17.143321.14985@nntp-server.caltech.edu> nyet@nntp-server.caltech.edu (n liu) writes:
>>tchuang@leland.Stanford.EDU ( Chuang) writes:
>>>   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?
>>What you're hearing is an excessive amount of clipping. You just need
>>to turn down the output level a tad.
>The resistor would be the proper way, I think.  But a lot of work! (at
>least for me)  I asked someone about recording and he told me he hooked
>up his walkman with the volume VERY LOW, and it worked out great.  This
>might be a good starting point, while you try to get the other imputs going

Looking back on my post, i realized that i had just increased the S/N noise
ratio of this group significantly... Yes, i was dead wrong about the 
impedance bit. It DOES matter, and you do need an extra resistor in series
(on either/both ends) to make up for this. Most line level devices don't
do too well trying to drive a 600ohm mic input - they don't have the
current capabilities. I think most line input impedances are in the
high kohms. So, while the resistor network works ok, you have to be a bit
careful how you hook it up. So the best way seems to be the op-amp route,
although if you could find it, a quality audio matching transformer would
do just fine (I have no clue as to the proper winding ratios yet).

What bugs me is that the mic input is certainly a separate stage in the
input, since A/D converters don't generally boast such high gain/flexiblity
in mics. It would have been easy to provide an intermediate stage for 
line level. I believe several Mac digitizers provide for this, for example.

nye