[sdiy] Quality reverb on STM32's?

[Olivier Gillet]

To give concrete number, the built-in reverb in Clouds and Elements use
about 6% of the available CPU on an F4 clocked at 168MHz, and 32k and 64k
of RAM respectively.

For a while I played a lot with FV-1s (it's a very, very clever design) so
I wrote some code that emulates the FV-1 programming model, to easily adapt
algorithms originally written for FV1 to C++ (For example:
https://github.com/pichenettes/eurorack/blob/master/elements/dsp/fx/reverb.h
)

On Sat, Apr 14, 2018 at 12:23 AM, Tom Wiltshire <tom at electricdruid.net>
wrote:

> +1 agree.
>
> The FV-1 chip pulls off some decent reverb algorithms, with only 1 second
> of delay memory at 32KHz. The secret in that case is Keith Barr’s inside
> track knowledge of “good reverb for cheap” and how to get the best out of
> algorithms by using all pass filters and so forth to “smear” the reverb. As
> Eric says, a lot of it is in the “tuning”.
> In terms of MHz, the FV-1 uses 128 cycles per sample, so that’s 4MHz -
> yeah, seriously; you can do decent reverb at 4MHz. At least, Keith Barr
> could and the rest of us had better catch up! ;)
>
> Example from Mick on DIYStompboxes:
>
> https://www.youtube.com/watch?v=0k69GtDoin4
>
> Tom
>
> ==================
>        Electric Druid
> Synth & Stompbox DIY
> ==================
>
> > On 13 Apr 2018, at 20:38, Eric Brombaugh <ebrombaugh1 at cox.net> wrote:
> >
> > It really depends on your definition of "quality". I've been able to
> build reverbs on STM32F4 and STM32F7 that sound like reverb but probably
> wouldn't have the cognoscenti turning cartwheels, but then I was just
> spitballing to see if it'd work and didn't spend a lot of effort on tuning
> them up.
> >
> > It all comes down to what kind of compromises you're willing to make -
> choice of algorithms, tolerance for short RT60, metallic / resonant
> artifacts, etc. Tuning up a reverb that sounds great is definitely an art,
> not science and the folks who do that will spend a long time to get it just
> right.
> >
> > For reference, the Spin FV-1 reverb chip has just 32k samples (using
> their crazy reduced-precision floating point format) of on-chip memory
> that's used for delay buffers and allpass filters. Those reverbs are
> passable if not fantastic. I was able to port one of their demo algorithms
> to an STM32F405 using only on-chip memory and it worked fine. With off-chip
> memory I'm sure you could do even better.
> >
> > Eric
> >
> > On 04/13/2018 12:25 PM, KD KD wrote:
> >> So when we the unwashed public finally have access to 32bit and SAI/I2S
> >> with large on board SRAM's i wonder how many Mhz and Kbytes do one
> >> need to make "quality reverb" on STM32? I'm thinking of how much is
> >> "enough" to make quality reverb with the known principles excluding the
> >> large memory sampled ones?
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