[sdiy] Using dual BBD chips for higher clock frequency

brianw brianw at audiobanshee.com
Sat Jun 25 07:28:13 CEST 2022

You don't even need the ARM processor.

Just wire up some address counters and simple digital logic to drive parallel memory R/W strobes from parallel ADC to parallel DAC. Granted, many converters these days are serial interface, but plenty of parallel interface converter chips still exist.

Vary the sample rate, instead of the memory size, in order to get different delay times. This mimics how the BBD works. A BBD always has a fixed amount of memory, but the clock rate varies. You can even change the address size of a digital delay to simulate swapping a SAD1024 with a SAD512 or SAD256.

You'll also only see a 1-sample latency (when desired) with the discrete DMA, whereas the ARM will almost surely need to buffer a number of samples before moving them around in memory (unless the ARM can literally address all of RAM with its DMA).

Lots of ways to skin this cat. Oops - wrong cliché ... I love cats!


On Jun 17, 2022, at 2:01 AM, Mike Bryant <mbryant at futurehorizons.com> wrote:
> BBD is only about 12 bits accuracy at best, and there's plenty of cheap ADC/DACs that can run 12 bits at many megahertz.    Pair one of these with a cheap ARM processor with lots of memory.
> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Jay Schwichtenberg via Synth-diy
> Sent: 17 June 2022 02:02
> To: synth-diy at synth-diy.org
> Subject: Re: [sdiy] Using dual BBD chips for higher clock frequency
> Isn't one of the advantages of using a BBD over a digital solution is the clocking can go to 500 KHz to 1MHz?
> So depending on the clock freq you can get the aliasing filters higher up and have better freq range.
> Jay S.

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