Hi everyone:

Has anyone here implemented a phaser in Csound?  By phaser, I mean a
device that uses several allpass filters in series, with sweepable
coefficients, and variable feedback around the allpass chain.  The
output is the original signal combined with the output of the allpass
series, resulting in several notches throughout the frequency spectrum. 
I have tried a few different implementations, that all blow up in
annoying yet amazingly uninteresting ways - no good noises, just a
sudden leap in amplitude (i.e. the signal's amplitude goes from the
normal range to 4 million to infinity).  The stable versions I have
tried are pretty boring sounding.  

If anyone has done this before, or has any pointers, please let me know.
I'd love to see your .orc files, or even C code that implements this.
(I'm not going to post my orchestras, simply because they seem
fundamentally flawed).

Thanks,

Sean Costello

P.S.  The only relevant literature I have found is an article by Mike
Beigel, "A Digital 'Phase Shifter' for Musical Applications, Using the
Bell Labs (Alles-Fischer) Digital Filter Module" in the September 1979
issue of the Journal of the Audio Engineering Society. Semi-interesting
trivia: Beigel was one of the founder of Musitronics Corporation, the