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Analog and digital flanger: differences….

December 8, 2012 | 11:51 am

Hi list,
working on a Max digital flanger, I realized that changing the modulation rate
affects also the modulation amplitude.

Example: changing the modulation rate from 1Hz to 2Hz I get an increasing of
the modulation amplitude, which will be 2 times wider.

This wouldn’t happens with an analog flanger…

Does someone knows how it happens and how we could solve the problem?

Thanks
fv


December 8, 2012 | 6:17 pm

It’s hard to say anything too concrete without seeing your patch. If I had to guess, I’d wager that you’re using tri~ or one of the other band-limited oscillators as your mod source. These are band limited, which include DC blocking, so that amplitude falls off with frequency when run at lower than audio rates. I posted this on another thread to illustrate the difference—

– Pasted Max Patch, click to expand. –

December 9, 2012 | 9:33 am

Hi Chris,
thanks for the post. Please take a look at the patch here included.
It is just the "wet" part of a flanger in which I used a cosine wave
as input signal.

In the sonogram is plotted the frequency articulation produced by
the variable delay line. Changing the Rate produces a wider Depth…

In an analog flanger, Rate and Depth are two distinct parameters,
so here there is a "unwanted" connection.

fv

– Pasted Max Patch, click to expand. –

December 9, 2012 | 12:52 pm

Hi Federico

The change of pitch depending on the speed of the modulation is the reality of an interpolating delay line. The speed relationship of tap point and the material in the delay line changed, in a way comparable to doppler. It is possible to correct for this effect, by multiplying with the reciprocal of the modulation speed.

– Pasted Max Patch, click to expand. –

December 9, 2012 | 4:12 pm

Thank you very much Jvkr!
I think the problem could be solved also using two sfplay, one of them
has a control oscillator of the frequency. The result could be similar to a
flanger.


December 9, 2012 | 6:52 pm

I don’t understand all the use of multiplies in your control structure. Here’s a simplified version:

– Pasted Max Patch, click to expand. –

December 9, 2012 | 8:08 pm

Chris,
your simplified version is not the one of the conventional flangers.
Normally we need to get a depth as percentage of the basic delay time.

My use of multiplications is similar to the one of the Max tutorials:
http://cycling74.com/docs/max5/tutorials/msp-tut/mspchapter29.html

Best
fv


December 9, 2012 | 9:53 pm

This tries to mimic the control structure of the MXR flanger:

– Pasted Max Patch, click to expand. –

December 9, 2012 | 10:51 pm

Thank you very much Chris,
it sounds very close to a traditional flanger!
Do you have a flow diagram of MXR flanger?
Could you sent it please?
Thanks
fv


December 10, 2012 | 7:19 pm

There’s a comment in the patch with a link to the site where I found the MXR schematic.


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