[music-dsp]

[Theo]

No your right, the DX7 was implemented in a gate array, 
not in a DSP or CPU.
When working in hardware multiplications are _very_ expensive,
while a adder is not. 
And lookups while expensive are the fastest way to generate 
a waveform or do a log <> lin conversion in the hardware world.

Theo



From: piter pasma ..ritz <ritz_rvl at yahoo.com>

> just to be sure... this sounds like a cool optimization, usable
> for a lot of things, not only ampmod..
> 
> but i just want to know:
> this isn't much use when you do DSP on the pentium FPU, right?
> [because both fmul and fadd cost 3 clockticks, and lookup-tables
> are probably a bad idea due to cache and all that]
> 
> i just wanted to know, if i could use the trick, when coding for
> a pentium FPU.. guess not :)
> 
> > Hi Richard. 
> > 
> > I think the first question is what do you want to achieve- e.g.
> > is it Yamaha-style FM synthesis? As far as I know, Yamaha
> > implemented
> > piecewise linear envelopes in their DX-series. Moreover, in order
> > to
> > avoid multiplications, the sine wave generators were based on table
> > lookup with log(sin(x)) stored instead of sin(x). Thus, it was easy
> > to implement amplitude modulation simply by adding logarithms and
> > come back to the linear realm by performing a second table lookup 
> > with exp(x) stored within.
> > 
> > MB
> > 
> > dupswapdrop -- the music-dsp mailing list and website: subscription
> > info,
> > FAQ, source code archive, list archive, book reviews, dsp links
> > http://shoko.calarts.edu/musicdsp/
> > 
> 
> 
> =====
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> ... ritz_rvl(at)yahoo(dot)com     ..
> .... http://www.ritz.nd-44-zh.net  .
> 
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