[sdiy] The Owl: ARM fx pedal

[Eric Brombaugh]

On 04/24/2013 11:57 AM, Martin Klang wrote:
> I've come across this presentation paper just now:
> http://www.arm.com/files/pdf/dspconceptsm4presentation.pdf
>
> It uses an example of a 7-band EQ (designed in Audio Weaver!).
> As compared to the M3 requiring 1291 cycles, the M4 performs this in 299 cycles.
>
> Perhaps as an illustration of chip capabilities, this would be more useful.
> We really just want to communicate an idea of what the chip is capable of, in terms of DSP, rather than give any exact benchmarks.
>
> In the paper they also show optimised FIR code which computes in 1.6 cycles/sample, as opposed to 12 unoptimised, but I think it would be misleading to present that as an achievable result in the general case.

I think that paper speaks for itself and not in the way that the authors 
intended - the complexity of hand-optimizing the ARM DSP code vs the 
simplicity of the traditional DSP code to which they are comparing 
themselves.

That said, I'm by no means denigrating the capabilities of the STM32F405 
MCU - I've used it in a number of audio projects so far and it is by far 
the best trade-off of cost, ease of use and features that I've come 
across to date. It is quite capable of handling a wide variety of audio 
processing tasks without requiring laborious optimization, and with 
optimization you could likely take it somewhat further. Just be aware 
that you're not likely to get the same sort of performance from the 
Cortex M4F that you would from something like a Blackfin or TMS320-C64x.

Eric