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Buzzer Trio

Posted by Trapper Zoid, 09 August 2012 · 452 views

While implementing the tone generators in software I figured there's little reason not to simulate the actual clock speed of the hardware, at least to begin with. It means doing about six times as many calculations, averaging out the half a dozen sound values to the single one at 44100Hz rate sent to PortAudio. But when we're talking about a few odd million calculations per second with today's processors it won't hurt to add in a few million more. I really doubt any CPU bottlenecks of the future will be in the audio subsystem.

The three tone generators and noise generator are up and running. I'll need to play around more with the noise generator to learn how to properly use it, but the tone generators seem straightforward enough. I hand-coded in a short music demo to test how it sounds:

Three Square Wave Moonlight Sonata (no voltage drop-off):
Attached File  moonlight_10000.mp3 (1.07MB)
downloads: 100
(I'm going to have to find or figure out a good way to represent sound data as commands, as hard cording everything in a big ol' integer array isn't the best solution.)

I've been playing around with simple ways of moving the sound beyond pure square waves to give the sound a bit of a more hardware generated sounding feel. So far all I've tried is a simple voltage drop-off, a method suggested in the Sega emulator page from the last entry. In hardware, the voltage when held will drift back towards zero. If you're using a float based internal representation for your sound data, it's pretty simple to mock that up by storing the output and multiplying by a fraction close to one (0.99...) every cycle.

In terms of effect, the multiplier morphs the square waves more towards being sawtooth, affecting lower tones more than higher ones (they have longer wave periods so the voltage is held away longer). And it also dampens the overall volume too, more noticeable for the stronger values:

Three Square Wave Moonlight Sonata (0.999 multiplier per cycle):
Attached File  moonlight_09990.mp3 (1.04MB)
downloads: 106

Three Square Wave Moonlight Sonata (0.99 multiplier per cycle):
Attached File  moonlight_09900.mp3 (1.03MB)
downloads: 99

Three Square Wave Moonlight Sonata (0.9 multiplier per cycle):
Attached File  moonlight_09000.mp3 (1.03MB)
downloads: 95

I think I like the sound somwhere between three or four nines: it's close to the original but with some more interesting edge to it. But two nines has an interesting hardware sound too, and the crappy hardware sound of one nine is a nice effect.




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