[sdiy] Mathematics of flanging

Brian Willoughby brianw at audiobanshee.com
Sun Mar 6 21:56:43 CET 2022

I'm not talking about 24-bit audio CODEC chips with oversampling. I'm talking about 20-bit and 16-bit ADC and DAC chips without oversampling. Some of these can sample at 400 kHz or even 125 MHz. Many of the classic outboard delay effects were designed before 24-bit or oversampling existed.


On Mar 6, 2022, at 12:36, Mike Bryant <mbryant at futurehorizons.com> wrote:
> Careful with how you do that - some DACs (I won't name names :-) hate jittery clocks and lose sync for their oversampling clocks.
> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Brian Willoughby
> Sent: 06 March 2022 20:28
> To: Richie Burnett
> Cc: synth-diy at synth-diy.org
> Subject: Re: [sdiy] Mathematics of flanging
> A single sample delay can be reduced by increasing the sample rate. Also, with a dedicated sampling circuit, there is no limitation that the sample rate need to be fixed. Modulation can be applied to the sample rate rather than the delay offset. This technique isn't cheap on a computer with a fixed sample rate audio interface, but dedicated digital delay pedals do not have the same limitations as computer interfaces.
> Brian
> On Mar 6, 2022, at 11:56, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
>> Yes, it is true that digital delays are not limited to whole (integer) numbers of samples. There are many DSP processes that rely on being able to calculate the value of a signal "between the sample points" using various interpolation techniques.
>> Indeed Chorusing and Flanging are two effects that benefit hugely from 
>> properly implemented fractional-sample digital delays. (Hint: Linear 
>> interpolation usually doesn't cut it.)
>> -Richie,
>> ---- Gordonjcp wrote ----
>>> On Sat, Mar 05, 2022 at 01:52:40PM -0500, Michael E Caloroso via Synth-diy wrote:
>>>> 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).
>>> I think you're going to have to clarify that a little.  You can make digital delays that go right down to a single sample and up to many many hours, and modulate them with absolutely no apparent stepping over that entire range.
>>> --
>>> Gordonjcp
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