[sdiy] super cheap synthisizers

[Dominic Tarr]

how did you reply to my email arive faster than my email being selt back to me? weird. you guys are so fast you defy physics.

> there would be lots of ways around not having enough resolution in "sample" >time, like making the first period slightly higher and the next one slighty >shorter, so it works out even. I'd imagen that this would probably sound >quite interesting too. <<< also as I expect to be using it mainly for bass so >I don't think having only 20 steps to have a 4kHz note is much of an issue.

> oooh NOW you've got me started....   ;^P

I would NOT assume that you could make one pulse 'shorter' and one 'longer'...
if you did it evenly... it would sound like a pulse of 1/2 the frequency you intended...with a non 50% duty cycle...

>If it was a random 'short-long' it would sound like sh!t.  (well to be >fair... I am known for saying things sound like sh!t that some folks >like...).  This would be 'jitter' in the frequency and would not be a good >feature.. OK to add it if you want 'that' sound..but if you could not avoid >it... really bad.

wouldn't it be like really narrow bands of white noise?, still, it probably won't have to happen. I'm all for experimentation, like what would it sound like if you could set seprate filter levels for the on and off parts of the pluse? you could make all sorts of new wave forms -> 303 style exp decay style saws and pulse/saw waves and all sorts of stuff. 

>I'm with the 'one micro per voice' camp. I'm not a software expert... but I >would worry that if you had two voices from one micro with fractional >detuning... they would tend to have problems as they became nearly out of >phase with each other.

>Some sample players have this effect. Trigger two instances of the same snare >drum on the Alesis D4... and they will flange at discrete intervals... NOT a >continuous spectrum.

that sounds interiesting.

>OTOH I did say I'm not a software guy so there....

>Now a neat, really low cost VCA for a single micro symth would be to >synthesize the envelope with a PWM output... and then chop that voltage with >an analog switch controlled by the VCO 'pulse' output. This was done on some >monophonic early Casio mini keyboards.  You can vary tone with different >pulse widths... and the envelope using DC level from the PWM out (filtered >with a cap).

I've done this with a positive and and inverted envelope, and two analog switches... the result is a bipolar wave that does not need a blocking cap to get rid of DC offset.

>TTL level is probably 10x the level you will need for a line level out, so a >couple of resistors will work. You will need to use a series capacitor to >remove the DC level or it will thump a lot...

thanks - Dom

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haha! good one.