Do you have a sample program?
Perhaps you need to stabilize the comb filter, i.e. multiply the delayed 
value by some factor smaller than one?

omalley.ronan@gmail.com wrote:
> Hey,
> 
> I'm implementing a flanger effect as part of a guitar effects processor
> on an ADSP-21364 development board.  A Flanger effect is produced by
> adding a single delay to the current input sample, the length of the
> delay is dictated by a sin wave which i have in aa lookup table. This
> implements a comb filter.
> 
> My problem is that on top of the desired output I am also getting a
> 'police siren' like sound which is a sin wave produced by the
> imperfections involved when the sin wave calculates a non-integer
> delay.
> 
> I have tried to overcome this problem using linear interpolation which
> was an improvement but not a complete solution.  I then implemented a
> 4-point cubic  interpolation algorithm which didn't seem to improve
> things much more.
> 
> My question is, can anyone suggest a decent interpolation algorithm
> suitable for this audio application?
> 
> 
> Many thanks 
> 
> 
> Ronan
> 

Hey,

I'm implementing a flanger effect as part of a guitar effects processor
on an ADSP-21364 development board.  A Flanger effect is produced by
adding a single delay to the current input sample, the length of the
delay is dictated by a sin wave which i have in aa lookup table. This
implements a comb filter.

My problem is that on top of the desired output I am also getting a
'police siren' like sound which is a sin wave produced by the
imperfections involved when the sin wave calculates a non-integer
delay.

I have tried to overcome this problem using linear interpolation which
was an improvement but not a complete solution.  I then implemented a
4-point cubic  interpolation algorithm which didn't seem to improve
things much more.

My question is, can anyone suggest a decent interpolation algorithm
suitable for this audio application?


Many thanks 


Ronan