Message-ID: <002c01c06f8d$6f923aa0$288701d4@g4jnt>
From: "Andrew Talbot" <G4JNT@thersgb.net>
To: rsgb_lf_group@blacksheep.org
Subject: LF: Re: Off topic - Soundblaster programming
Date: Tue, 26 Dec 2000 22:44:40 -0000
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

I don't know about the mic input, I woulf have thought an ALC action on this
input was rather dependant on the particular machine / soundcard in use, but
it certainly does not apply to the line input  - at least I've never seen it
on a wide range of soundcards over the years.

Do you ned to make your measurements in real time ?   If you can save to a
.WAV file using a prog like sound recorder, or even Spectrogram, you'll have
a lot more flexibility in what can be measured.   The .WAV file has quite a
straightforward file structure if you want to write your own software.

I have made considerable use of this technique for comms signal analysis and
synthesis and never had any non-linear effects other than those caused by
genuine analogue side problems !

Andy  G4JNT


>
>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
>
>
>
>