[sdiy] Mathematics of flanging

Michael E Caloroso mec.forumreader at gmail.com
Sat Mar 5 19:52:40 CET 2022


The key to extreme flanging sounds is inversion in place of the summing
node.  Many delay units do not include inversion.  The inversion produces a
radically different frequency response.

But a real "jet flanging" effect - same as the classic technique using
analog tape players - needs a minimum of TWO delay elements.  The concept
of the flanging effect heard by a listener in a fixed position relative to
a jet airplane in motion was laid out in Electronotes #56 pg 12, so I
attempted to implement it with my Korg SDD-3300, a very flexible triple
digital delay.  See attached.

The result was flanging but the effect was mild.  In Device Magazine volume
1:10:79 pg 10, Stephen St Croix - inventor of the CCD-based Marshall Time
Modulator effect processor - lays out the crucial criteria for effective
jet flanging effects.

Digital delays aren't ideal because you can't get deep enough modulation,
the modulation LFO in digital domain is often too discrete at low sweep
rates, and you need ~0.3ms delay (few digital delays offer short delay
times).  BBDs aren't ideal because the amplitude of the direct and delayed
signals must be matched within 0.1dB for widest notch bandwidth in the comb
filter effect.  Also the bandwidth of delayed output must be as wide as
possible for deepest nulls in the comb filter effect.  The deep nulls and
wide bandwidth of the notches result in more extreme flanging effects.

Granted, from the Electronotes concept the two delays will need some
filtering to emulate the two delay paths between listener and jet airplane,
especially the reflected path.  Also the Electronotes concept does not take
into account other indirect reflections.

The Marshall unit used CCD based delay elements to meet these criteria -
dual independent delays, smooth/deep LFO modulation, wide bandwidth, and
precise output matching.  CCD and BBD elements are bucket related, but
operate differently.  Each sample charges the storage capacitor of each BBD
element, while each sample DRAINS the charge of an initially fully charged
CCD element.  CCDs are also much quieter.

Effect connoisseurs report that the Marshall Time Modulator delivers the
best "jet flanging" effect.


On Sat, Mar 5, 2022 at 1:36 AM Lanterman, Aaron D via Synth-diy <
synth-diy at synth-diy.org> wrote:

> I just put together a lecture on that, if you’re into that kind of thing:
> https://youtu.be/LRZW31_aAnE
> Aaron Lanterman, Prof. of ECE, Georgia Tech
> My blog on Education and Innovation: https://edupocalypsenow.wordpress.com
> My blog on Electronics and Programming: https://lantertronics.blogspot.com
> My YouTube channel on Electronics and Programming:
> https://www.youtube.com/c/lantertronics
> _______________________________________________
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