On 9/11/06, Damian Stewart damian@frey.co.nz wrote:

you know the way a Mac laptop power light kind of 'snores' when it's in sleep mode? normally to make a light fade in and out like this you adjust the voltage up and down. but since you only have two possible voltages on a digital device - on (+5V or +12V or something) and off (0V) - you have to create the inbetween voltages by flicking on for a portion of time then off for a portion of time. to generate a +5V signal on a +5V digital output, turn it on all the time. to generate a 0V signal, turn it off all the time. to generate +2.5V, turn it on for 10 microseconds, then off for 10 microseconds, repeatedly - and then low-pass filter the output (using a capacitor and a resistor). to generate +1.25V, turn it on for 5 microseconds, then off for 15 microseconds, repeatedly, and low-pass filter the output - you get the idea, hopefully.

this is how the snoring power light works - the light is actually flicking on and off thousands of times a second but your eye acts as a low-pass filter and mixes them all together into a continuous glow... and theoretically you can do the same thing to get a control voltage for your Moog.

This is awesome. I get it now. Though I'm not familiar with the sleep light on Mac laptops, unfortunately. Would it be any harder to use the DAC output, converting the voltage from that? It has a low-pass filter, albeit one I can't control. But then I don't have to look up all those serial port connection diagrams. I have to write music some time during all this!

...

I don't know exactly how a Moog's PWM works, but from his description I thought I might just as well generate sine, ramp, square, triangle and pulse waves in Pd and run them through the filters and envelopes on the synth. And where's the fun in that? But if no other possibilities work out, I can use that.

Since it's largely the filtering characteristics (and the hum, and the noise) that make analog gear sound 'analog', that's not actually such a bad idea.

It's sounding better and better. I like the idea of being able to use the FM possibilities of the oscillators, though, and I actually think the guy teaching me the Moog might be offended if I suggest using digital synthesis, lol.

Thanks. -Chuckk