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
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