[sdiy] Shepard Function Gen's

[Chris Crosskey]

One way to do it would be with something like the circuit that Digisound
used for the saw-tooth multiplier....it was designed as a sort of chorus
unit that added whatsounded like six slightly detuned sawteeth waves to a
saw input.....basically it was shifting the sawtooth waves by using
different turnover points, then moving the turnover points with six slightly
different LFO's, hence the phases all shifted around wrt each other wihtout
ever locking into out of phase cancelling....WHat you want to do is to use
the trick with fixed turnover points all 45 degrees apart, then use your new
sawteeth to create a set of triangles to form the VCA controllers (heck you
might as well build in the VCA's too)....it's a good idea to put an LPF on
the sawtooth itself, it'll kill the switch glitch that might otherwise be
very hard to get rid of, and you don't have to worry too much about it
causing a slew rather than a straight cut at the turnover point as it'll be
inaudible at that point anyway....you might as well build a dedicated LFO to
power it limited to useful Shephard frequencies....I doubt it needs to go
audio, I doubt it needs to be that slow either.....

chrisc 

> -----Original Message-----
> From: Lewis Bupp [mailto:lbuppii at hotmail.com]
> Sent: 11 March 2002 02:55
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] Shepard Function Gen's
> 
> 
> Many years ago, Paia sold a Sheppard (SP??) Function 
> Generator kit or IC. 
> They no longer sell the chip. IS the chip still manufactured? 
> If not, does 
> anyone know of a circuit that will approximate the same effect?
> 
> Lew
> 
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