The Cortex Ms are very tempting due to the modern support and low cost tools, but if you need serious filtering the DSPs will be a better option. Actually, depending on what you need, the options above may not be even enough to get the job done. However, we have to make the best with what we have.
So what kind of DSP do I need if I want to do serious filtering? At what sample rate and word size you are talking about?
For regular stereo 14 or 16-bit audio from 22 to 44.1kHz, the fixed point options you are considering where quite enough for a number of filters and effects. I can't precisely recall all the nitty gritty details, but IIRC I was able to add five-six band equalizer with room for echo, chorus and reverb, but there was a tradeoff between the equalizer bands, the effects depth and the auxiliary functions (USB, SD card, etc.). The BIOS RTOS helped a lot balancing these tradeoffs - adding or removing functions (threads) was easy.
BTW, I found some of the libraries for this device -
hereOne additional detail I forgot to mention is that there is a version of the C6748 DSP I mentioned before with an ARM9 core in it - useful to run full Linux (not uCLinux). The benefit is they are pin to pin compatible.
I have found that - part of OMAP line. I am not yet ready to design my own boards with big BGA packages like that now though.
Yeah, I forgot that. The BGA is the Achilles' heal of these more advanced processors.
For audio I'm sure the CM4/CM7 will do perfectly fine with their fixed-point SIMD instructions - and he gets a competent application processor with many excellent sources and varieties to boot. Unless it's going to be doing something unusually complex.
bson, talking "For Audio" is too generic of a statement - the level of complexity can increase quickly depending on what you want to achieve, from a simple lowpass filter to an adaptive echo cancellation, plethora of effects, multichannel, high sample rate...
I've considered this path for DSP effect, interpolation and sigma delta modulation for my from-scratch sigma delta DAC project, and the result is DSP is better.
CM7 is great, but not as good as BlackFin+, even when processing 32-bit values. CM7 is better than classic BlackFin DSPs when dealing with 32-bit MACs since the old chips don't have single cycle 32*32+72 support.
Most CM7 don't run at 400MHz frequency like those BlackFin chips (spare iMXRT and 416MHz STM32), and they don't have modulus addressing mode, which is a big set back for FIT filters. Also, they don't have bit reversal addressing mode, which is offered in BlackFin DAG.
My experience with Cortex cores is very similar. Although Cortex cores can scale much better (a Cortex A can go much higher in speed), much of the raw performance gained in MAC speed is reduced when trying to resolve the more complex addressing modes.
I've also evaluated TI parts, but TI single chip DSP parts (not those needing an external RAM) don't have high speed USB, which is crucial to me.
Did you evaluate C2000 DSPs? They would be quite slower in performance.