[sdiy] harmonic generator

[Scott Gravenhorst]

media.nai at rcn.com wrote:
>
>>Can anyone recommend a harmonic generator circuit - I need about the
>>first 10 harmonics of a given fundamental.
>
>I've been trying to do this for awhile.  If anyone has schematics for the
>Buchla 185/285 -- you let me know!!  Serge had one in their catalog, but I
>do not know if they ever made one.
>
>>1. Phase Lock Loops
>
>I tried that.  You need to run the input through comparator, then through a
>pulse divider into the PLL, then put another divider in the feedback loop
>of the PLL, then shape it into sine.  You need one of these circuits for
>each harmonic, although you can use logic to change the divider values.
>Besides shaping the sine, 


>the trouble is the lag of the PLL, which is quite audible.

The filter you are using might not be optimized.  I used an 
RC filter with a *pot* for the damping resistor.  It makes
a difference.  The portamento can be almost eliminated.  I
found a very short portamento to be interesting as part of
the attack.  In other words, no, it is not *perfect*, but
it is quite useful.

Also, you don't need one for *each* harmonic.  Eg, 1, 2, 3, 4, 6 
& 12 are easily done with one PLL, 5 & 10 with another, etc.  
There are many ways to approach this, but you can do it with less
than 10.  I have a circuit at:

http://home1.gte.net/res0658s/FatMan/4046pll.html

This generates 1, 1.5, 2, 3, 4, 6, and 12 times the input
frequency with one PLL.

>>2. Walsh function to sine
>
>What's a Walsh function??

Binary counter driven by an oscillator, divider outputs
are combined with XOR networks to provided different wave
forms.

>>3. Divider chains
>>4. Look up tables
>>5. Rate multipliers
>
>How does a rate multiplier work??

these are devices that actually divide a clock by some
integer value.  The output is a train of (not necessarily
evenly spaced) pulses that over time represent a rate
lower than the clock input.

MC14527B is one example.  This one is CMOS, I believe there
are TTL ones too.  See the data sheet for wave forms of
output.  I've not sure they're musically useful.

[snip]
>
>Wouldn't full wave rectification simply result in octaves??

Yes.

>>What you'd need is the electronic analog of a big
>>gearbox that has output shafts at 1, 2, 3, 4, etc
>>times the input RPMs...
>
>LOL!!  Is there a transmission-diy list?? :)

I was hoping one of the trig heads here would pop up...

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