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Amp signal to swing between set values
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laejf:
Hi. I'm wondering if there is any way of automatically amplifying an audio signal to vary between +-3.3V. I'm working on a signal sampling circuit and would like to increase the signal to noise ratio as much as i can. The problem is that i'm only able to use the circuit with an oscilloscope since the signal vary with the volume set on my computer and i need to adjust the resistance connected to an OP amp to keep it in the wanted interval. I'm guessing some sort of feedback could be involved by i cant come up with any and i dont know what to google for.

The set interval of +-3.3V is the lowest voltage my sampling signal can go, it's a sawtooth-wave that a comparator compares against my audiosignal.

How does a consumer level sampling circuit work? Does it sample the low level audio signal that can be as low as 10mV in my case? That has to introduce a lot of noise.

Would be very glad for ideas! Thanks
Ian.M:
A keyword you may want to look up is: compander
https://en.wikipedia.org/wiki/Companding

EmmanuelFaure:
Yes : https://en.wikipedia.org/wiki/Automatic_gain_control
David Hess:
An AGC (automatic gain control) loop comprising a detector, comparator, and gain control element can do that.  This is a pretty common function.

In your case the detector should measure the peak-to-peak value which is easy enough.  The gain control element could be an operational transconductance amplifier or Gilbert cell multiplier.
SilverSolder:
The circuit you are looking for might be called either an "Audio Compressor" or "Automatic Gain Control" (AGC) - you can google that and find tons of circuits on the Internet.
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