[sdiy] Digital Synth Module ideas ...

[Seb Francis]

jbv wrote:
> As for digital fx module, here's something I've had in mind
> for a while : a simple  AD -> uC -> DA structure, but the
> software would include all kinds of crazy math computations
> on samples, like average of the n last samples, log of sample
> value, etc.
> The software could even have some modularity, IOW it
> should be possible to put several math fonctions in serie...
> The result would probably be some ugly digital distortion,
> but who knows...
>
>   

Any other particular computations you had in mind?  My experience with 
playing around with arbitrary maths functions has generally been "ugly 
digital distortion", but this can't be true for all maths functions :)

The best way to try out these ideas would be on a PC .. I think on Linux 
in particular there are utils that will let you manipulate wav sample 
data using simple scripting languages, and hear the results.

Andre Majorel posted some samples recently of what it sounds like doing 
various bit-swap operations (link anyone?).  Unfortunately again mostly 
ugly digital distortion.

The "average of the n last samples" would be a low pass filter of some 
kind.  This is how you make a normal FIR digital filter - take the 
weighted average of the n last samples - the weighting coefficients 
define the filter response.  But personally I wouldn't implement this in 
digital unless I had to - I have many nice sounding analog filters in my 
modular already.

Log of sample value (or indeed any kind of mapping of single sample 
value to a mathematical function) would mostly produce strong digital 
distortion (but hopefully not ugly in all cases!).  I wonder about 
mapping to a sine function ... e.g. if you have a triangle wave input 
you would get a sine wave output.  Anyone try this with other audio inputs?

Seb

P.S. Andre, what software did you use to do the bit-swap stuff?  I have 
cygwin installed, so I'd like to try out some of these ideas before I 
bother coding them in assembler!