Smart Voltage controlled Amps

[Mosaic]

In another thread I was interested in auto gain control circuits.
Well this page:
http://www.idea2ic.com/LM13600/UsingOTAs2.pdf

Tells me that a uC with a DAC out or even a PWM equivalent can control analog amplification.

Does anyone have any experiences doing this?
Using a uC can enable creating matrix tables to map nonlinear analog inputs into linear analog results for metering etc.

 

[ronsimpson]

For a while I played with using a THAT4301 and a micro controller to make a audio compressor/limiter. The THAT4301 has some smart parts but I wanted to dynamically adjust the "attack and decay time" and add squelch using "software". By using "soft" time constants it is easy to program audio circuits on the fly.

It may be wiser to do the whole project with a DSP.

 

[MrAl]

Hi,

Back in the 80's i had designed a solar array max power tracking circuit using a CA3080E but those are obsolete now i think. Shows how much people liked using them

I always wanted to try one of those "audio" gain control devices which are made from an LED and photo resistor and they were made for audio compressors and the like. Never got a hold of one yet though. From what i gather they are simply an LED and photo resistor in a sealed up package so no light get get in, and the photo resistor is of course electrically isolated from the LED so it can be used any way you want in the feedback of an op amp for example (or whatever) to very the gain with a DC signal to the LED. They should make a nice linear gain control (linear with respect to the audio as well as the LED current control).

You could also look into PWM gain control too i guess, where you vary the on/off time of the audio signal to vary the gain. The switching frequency would have to be much higher than the audio. This would only require an analog switch and a uC chip (and simple passive band limiting filter).

 

[audioguru]

The audio digital compressor/limiters used by most TV stations today sound awful. During a pause in speech, they seem to increase the gain quickly so that background noises are heard. But when the speech continues or even when the person takes a breath they cut the gain slowly down to normal. The result is that the first syllable of almost every word or taking a breath starts too loud then as the gain is slowly reduced the last part of each word sounds normal. The beginning of each word or a breath sounds like a hammer or a hurricane (monsoon?).

In "the good old days" the compressor/limiter was analog and its gain control was the opposite of the new digital ones. During a pause in speech or between words the gain changed very little because it has a slow release. But when a louder than normal sound occurred then it reduced the gain quickly because it had a fast attack. It sounded natural.