For more context, dsp chips historically were how you could get better better performance than was typical in the embedded space. At a time when you had sub 100Mhz typically in a chip that would be used in musical equipment dsp chips were super useful because they had many op codes that could be done in one cycle that might take many multiples of that in a general purpose chip. One prime example is add and accumulate. This meant that effectively, if you had an 80Mhz dsp doing calculations for you, you effectively had a 160-240mhz equivalent in your hotpath. This bump up in processing is necessary to meet hard realtime deadlines in audio processing at 48khz stereo processing.
Now, processors are so fast and cheap, that the need for dsp is way down. I personally ported the firmware for a popular pedal where the chip used was no longer available at quantity, and while it was tricky to get the same performance on a dual core 240mhz processor with floating point coprocessor, as the 96Mhz processor it was replacing, I just had so much compute, that I was able to port all but the gnarliest simultaneous effects on a chip that cost $6 cheaper but also came with enough ram to not need that $3 component either. And I can tell you, saving $9 dollars off a BOM means the product can retail at least $50 cheaper in an industry where volume matters a lot (no pun intended).
We have passed the inflection point where dsp chips are generally not worth the cost in most audio equipment. I’m not sure I’d use a raspberry pi, their reliability is not what I’d want in my products, but a similar single board computer? maybe. I’m not sure where linux realtime kernals are at the moment, ignoring the added complexity of a full linux running to process audio, audio requires hard deadlines. You will hear pops and other artifacts if you miss these deadlines, and buffering audio is also not something you can do for long, artists can feel delays in the ms. But, a single board computer running at ghz speed, gives an awful lot of compute so long as the OS can gaurantee your audio thread won’t get starved.