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From: omalley.ronan@gmail.com on 15 Feb 2006 11:28
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

From: twain on 20 Feb 2006 01:35
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(a)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
>
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