[sdiy] IR Reverb

rsdio at audiobanshee.com rsdio at audiobanshee.com
Fri Feb 16 22:48:46 CET 2018

You really need a DSP for this, and not a general-purpose CPU like ARM. Even though ARM has a DSP instruction or two, it's a far cry from a total system designed for signal processing. Families like the TMS320 have been evolving for decades - literally 35 years - to optimize this sort of thing. Literally every aspect of the chip has been tweaked to optimize signal processing.

Texas Instruments has cheap demo platforms with audio I/O and the tools come free with those $50 evaluation boards. There are a lot of open-source routines, so if you need FFT in TMS320 assembly then it's there. You can call that from C and keep your overall design simple.

Texas Instruments even has chips that are dual-processor inside - one TMS320 for DSP, plus and ARM for the higher level stuff and maybe even some audio processing. Look for OMAP chips. The C6000 series of DSP would be a good choice because it supports floating point (I've worked with the C5500 series that is fixed point, and that's a lot of tedium but worth it if you want to run off of batteries).

Another good option would be SHARC.

If you choose a non-DSP chip, everything will be less efficient. That either means loss of features or higher temperatures and shorter battery life.

Brian Willoughby
Sound Consulting

On Feb 16, 2018, at 11:47 AM, Tim Ressel <timr at circuitabbey.com> wrote:
> I wonder if it would be possible to do a parallel processor scheme where one proc handles the early stuff and another to handle the longer time stuff. each proc would output via a codec and those outputs would get summed. Hmm...
> On 2/16/2018 11:38 AM, Eric Brombaugh wrote:
>> I suspect that STM32 doesn't have the horsepower you'll need to do a useful IR reverb. There are several fairly efficient FFT in the CMSIS libraries from ARM but even using those the best you can do is about a 4096 FFT running at less than 48kHz with long latency and large overlaps.
>> On 02/16/2018 12:24 PM, Tim Ressel wrote:
>>> Still, even with all that jigery-pokery, we're going to need a bigger boat, er, processor. I'd like to avoid processor choices that needs pricey tools. STM32 would be nice. Of course some good ol' fashion assembly code, highly optimized, would help things. Its been a while since I went down that rabbit hole. I wonder if someone has an optimozed FFT library for Cortex Mn…

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