[sdiy] Mathematics of flanging

[Pete Hartman]

Thanks for that Michael.

I've tweaked the image so that the contrast is a bit more readable, I
figured I'm not the only one whose vision needed such assistance, so here
it is :)

Pete


On Sat, Mar 5, 2022 at 12:57 PM Michael E Caloroso via Synth-diy <
synth-diy at synth-diy.org> wrote:

> Nice.
>
> 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.
>
> MC
>
> 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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