Jean-Michel DARRÉMONT wrote:
> 
> Hi,
> 
> Does any one knows how to simulate a spectral enhancer(Aphex type) in CSound.
> Are there orc&sco on this subject around there or, more generally, is there
> any documentation on the subject (books,web, usenet,lists etc...).

Your best bet is to search http://www.patents.ibm.com for the keyword
Aphex, and see what turns up.  The different spectral enhancement
methods are usually not discussed by the companies in question, but a
little creative patent searching should uncover some good stuff.  

The original Aphex patent is

http://www.patents.ibm.com/details?&patent_number=4150253

>From what I understand of the Aphex-type boxes, they work through a
combination of filtering and nonlinear distortion.  One variant uses a
highpass filter, followed by 2-quadrant modulation of the signal with
itself (thus doubling frequencies, and adding more high-frequency
energy).  Other versions simply use a highpass filter followed by diode
clipping; this could be simulated in Csound with a highpass filter,
followed by table lookup into the distortion function of your choice. 
You might want to try running a signal through a filter, then using this
filtered signal to modulate a deltapi delay line that the signal is
going through.

The big problem with trying to do this sort of spectral enhancement in
Csound would be aliasing.  The process depends on generating new
high-frequency harmonics of the signal, which could very easy alias and
end up sounding lousy.