[Jack-Devel] Fwd: Variable delay line problem

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DateSat, 14 Apr 2012 14:56:12 +0400
From Stéphane VAXELAIRE <[hidden] at free dot fr>
To[hidden] at lists dot jackaudio dot org
Follow-UpMatthew Robbetts Re: [Jack-Devel] Variable delay line problem
Maybe I could reset it to 0 each time the sine cross the axis thus having only cos values between 0 and 1 or -1 and 0... Can't try right now...

Début du message transféré :

> Expéditeur: Stéphane VAXELAIRE <[hidden]>
> Date: 14 avril 2012 14:51:41 UTC+04:00
> Destinataire: Friedrich Ewaldt <[hidden]>
> Cc: "[hidden]" <[hidden]>
> Objet: Rép : [Jack-Devel] Variable delay line problem
> 
> Thanks for the Matlab example that's the most explicit I've seen.
> 
> I guess I have the algo right (not 100% sure though) thanks to you and Chris.
> Now my problem seems to be with the 'n' variable.
> 
> I understood from the Matlab example that it is simply a counter from delay buffer length to size of the audio file.
> Now, I'm operating on jack buffer that are 512 samples long. So I can't simply rely on that.
> 
> How an I maintain such an increasing global var if my sound source is my computer line in for instance ?
> Can I modulo it to something ?
> 
> Thank again
> 
> Le 14 avr. 2012 à 13:32, Friedrich Ewaldt <[hidden]> a écrit :
> 
>> Chris Caudle schrieb am 13.04.2012 23:29:
>>> On Fri, April 13, 2012 11:52 am, Stéphane VAXELAIRE wrote:
>>>> Thanks, I did try that, but when I do, the sine does not seem to evolve.
>>> 
>>> Maybe I suggested the division in the incorrect location.
>>> I tried the equivalent in Octave, and it seems to work with:
>>> cos(n/Fs*2*pi*freq)
>>> 
>>> I don't remember how operator order of precedence works in Octave, so I
>>> also tried:
>>> cos(2*pi*n*(freq/sample_rate))
>>> 
>>> and that also seemed to work like expected.
>>> 
>>> By work as expected, I just mean it generated cosine values of the
>>> expected period.  I did not try to actually implement a variable delay so
>>> that I could make a flanger in Octave code.
>>> 
>> 
>> If you are looking for a flanger implemented in Matlab (most probably works with litte or no changes also in Octave) you may take a look at e.g.
>> http://www.mathworks.com/matlabcentral/fileexchange/6656-flange-effect
>> 
>> or this nice presentation containing flanger Matlab code as well:
>> 
>> http://www.cs.cf.ac.uk/Dave/CM0268/PDF/10_CM0268_Audio_FX.pdf
>> 
>> or in general:
>> 
>> http://www.google.com/search?q=flanger+octave+OR+matlab
>> 
>>> Are you doing any prototype code in Octave, or is everything in C?
>>> 
>>> Also, I didn't really pay attention to how you were implementing the
>>> delay.  I had assumed you would do an interpolated delay so you can make
>>> smooth phase adjustments.  If you are just grabbing samples from the delay
>>> buffer, you are going to have discontinuous jumps between samples, and
>>> that is going to sound really bad, just like having lots of under-runs
>>> (same effect, you are just skipping over some samples and not playing
>>> them).
>>> 
>> 
>> 
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