Message-ID: <3A48E4C7.1BD37753@virgin.net>
Date: Tue, 26 Dec 2000 18:34:48 +0000
From: "Stewart Bryant" <stewart.bryant@virgin.net>
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To: rsgb_lf_group@blacksheep.org
Subject: LF: Off topic - Soundblaster programming
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I know that it is off topic, and I apologies, but there is a good
chance that the expertise will be on this list, and its always
best to ask friends first.

I am trying to measure the absolute value of an audio signal
using the sound (microphone) input on my PC. (For a radio
application, but not LF).

Having beat my head against various brick walls until 2am the last
few nights I now have a program that can get the samples from
the sound card. After further beating of head, I discovered that
the reason that I was not seeing the linear change with amplitude that
I was expecting was because there is some sort of vogad action
in the microphone audio input. Does anyone know:

1) How to turn this off
2) If the same applies to the line input

If anyone has an example program for simple audio input via Vbasic
that would be even better.

There is a Vbasic code example that shows the use of the volume
feature of the SB card to measure amplitude, but when I tried
it (before I realised that vogad was going on) it seemed
to have some strange semi log characteristic (ie it stayed constant
and then suddenly increased as I varied the amplitude through the
mixer control). Has anyone else had any experience making linear
measurements through this feature?

Thanks in advance to anyone that can help

73

Stewart G3YSX