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implementing frequency modulation in a delay path?

May 18, 2010 | 2:04 pm

hello everyone

im pretty new to all this stuff but i thought i’d give it a go as i have always wanted to build my own VSTs, etc. Anyway, i’m trying my hand at emulating (or trying to) a tape delay and am having difficulty in implementing frequency modulation into the feedback loop and i have tried and tried and all that happens is the audio drops out and everything is unhappy until i disconnect it.

has anyone tried this or know what it is im doing wrong?

thanks

Hugo


May 18, 2010 | 2:31 pm

Sounds like you have an "illegal" feedback loop. Try using tapin~ to tapout~ or send~ and receive~ in your feedback loop. Send~ and receive~ introduces a delay of one signal vector which allows the audio signal to be fed back to itself.


May 18, 2010 | 2:48 pm

its really odd – i am only using send~ and receive~ and all other effects (dist; amp mod; filt) work fine. it is just the freq mod that makes it bad. in all honesty, i am not entirely sure that i have connected the patch into the loop correctly which is why i think it is giving me problems. it is also odd that when i directly connect the freq mod patch to the tapout~ inlet, the feedback loop is modulated but i obviously loose control of the delay parameters which i don’t want to do. i am confused about the freq mod because i have never had to do it like this, i have implemented it into synthesisers but i don’t really know how to use it here. sorry – i am, like i have said, very new to this…


May 18, 2010 | 2:54 pm

Can you post your patch so we can give you some concrete feedback? ;)


May 18, 2010 | 2:58 pm

aha-let me just have a tidy up and i’ll sort something out. any other pointers would be welcome too ;)


May 18, 2010 | 3:23 pm

right – here is the delay line

[attachment=132763,559]

Attachments:
  1. delay.bmp

May 18, 2010 | 3:24 pm

as you can see i have left the freqmod disconnected


May 18, 2010 | 3:25 pm

and here is the freq mod patch


May 18, 2010 | 3:27 pm

this is definitely wrong… i know it is. i just don’t really understand how it needs to be implemented. to be fair – i used to do a bit of MSP a few years ago but am rusty as they come.


May 18, 2010 | 3:28 pm

woops, need to actually post the damn thing.

[attachment=132767,560]

Attachments:
  1. freqmod.bmp

May 18, 2010 | 4:26 pm

You probably mixed up frequency modulation and ring modulation.
For FM you modulate an oscillator’s frequency (or it’s phase aka phase modulation).

For Ring-Modulation you simply multiply one signal with another (typically a sine).

In your patch you add "frequency" to your modulating signal and add that to the original signal. So "frequency" will end up as a nasty DC-Offset.


May 20, 2010 | 9:11 am

 
he invented DC modulation^^
 

btw, you could use a signal to cotrol tapout (try putting a [line~] before it) that
gives you more options.
and with tapout, always make sure, you do not feed too short arguments for the
buffer (<10 ms or whatever it is at your samplingrate and vectorsize settings), that
can crash or crackle.


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