I'm doing this simply out of curiosity and my interest in old synthesizers....
Question one:I recently put together a yellow LED and an LDR from a dollar store light to make a simple little Resistive opto-isolator (Vactrol) that in turn controls the frequency of an oscillator.
I'm using the audio output of my computer to control it. I just used a plain old 2N2222 to make the LED blink with the sound like anyone would when first starting to mess with transistors and LEDs.
What would be the best way do this and make sure I get the full range of the LED from all the way bright to fully off?
I used a square wave from a software synth and adjusted the PWM to make the LED get brighter and dimmer (as you'd expect) and I found that even simply changing the volume of the softsynth fades the LED better than I was expecting. It's more finicky than PWM because it only works over a very small range of volumes but at least it's not flickery. I found that an LDR will pick up even the fastest flickering when you're in the relatively low frequency world of audio. A lowpass filter smooths out the flicker but it also changes how fast it reacts.
Question 2:Is there a better way to make a controllable resistance with an audio signal without using a vactrol type device? LDRs are very slow