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ModDelayModule
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lppier
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January 27, 2016 - 9:09 am
Member Since: December 21, 2014
Forum Posts: 23
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Hi Will,

I'm reading your ModDelayModule, and I understand how the pitch shifting works for chorus.
Is there any way to know/calculate how much pitch shift I am doing with respect to the original signal when using ModDelayModule?
Thank you.

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JD Young
Leiden, The Netherlands
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January 27, 2016 - 2:39 pm
Member Since: November 5, 2014
Forum Posts: 80
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Hi Ippier,

Interesting question. Never looked into it before, but I've tried to come up with the answer. In one of my dsp books it’s said that a max modulated delay variation – with a sinusoidal LFO! - of 0.265 ms (in either direction), produces a 1% frequency variation (up ánd down). Now, I’m not sure how they calculated or measured this, but let’s say for now it’s correct to use this as a linear scaling variable (@Will & Tom, is this in fact correct?). Then we could calculate the pitchshift the following way in pseudocode:

Find out max modulated delay variation in ms, and calculate frequency variation in percentage:
Variation_pct = variation_ms / 0.265

Convert frequency variation in percentage, to scaling factor:
Variation_fctr = 1 + Variation_pct / 100

Calculate pitchshift in semitones:
Pitchshift_st = Log2(Variation_fctr) * 12

Example: say we have a max delay variation of 0.5 ms.
Variation_pct = 0.5 / 0.265 = 1.887 %
Variation_fctr = 1 + 1.887 / 100 = 1.0187
Pitchshift_st = Log2(1.0187) * 12 = 0.32 semitones

As I said, I’m not sure if we can use the 0.265 ms = 1% frequency variation the way I did. But if this is not to be used in a linear fashion, it shouldn’t be that hard to adjust the calculation. Hope this at least helps you on your way!

Cheers, JD

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W Pirkle
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January 27, 2016 - 8:06 pm
Member Since: January 28, 2017
Forum Posts: 391
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You can study this paper for more information (as well as abundant references):

https://ccrma.stanford.edu/~dattorro/EffectDesignPart2.pdf

In addition, any simple pitch shifting calculation would only apply to a triangle LFO. Using any other LFO would result in nonlinear shifting as the speed of the pitch change would depend on the LFO shape.

- Will

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