wow that’s awesome, would open up the possibility to use higher spec speakers and would sound amazing.
you must spend hours trawling though material to find this type of gold! (i tip my hat to you sir!)
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Most of the time I prefer to use chips which have been well tested by other people, so I always start by looking at what breakout boards are available at sparkfun, adafruit and friends. After that it gets harder…
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Could that be used for realtime pitch change and filtering?
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Filtering: yes
Pitch change: no
Pitch change has to be done before mixing the audio.
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IF you are going that route, may I ask to “bundle” common pins next to each other? Like all the OLED, BlueTooth, the three typical Data (blade, PCB and Plade Present), etc? And please make battery charge a built in thing. Or at least easy to put an USB-C to do it all. I find that cable soldering and routing is the most time consuming part of a build. Having htem easily next to each other and needing a single port for charging, programming and loading soundfonts is what makes it really flexible.
I group the pins when I can, but placing the pads where it makes the most sense sometimes makes routing the board impossible, so I often end up re-organizing the pads to make routing easier. (Sometimes several times.)
USB-C ends up being bigger, more expensive and makes extending the wires a lot harder. The only advantage I’m aware of is that most people have the cables already.
USB charging is already a part of the V3 board, and will almost certainly be a part of any board I design in the future.
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USB-C is also reversible.
The nice thing of USB-C (besides reversibility), is the total power and the possibility of separating the power signals to a different charging circuit, thus enabling a killswitch while charging. This is the old way to charge the batteries. But now that I think about it, I should have wished for actual deep sleep. 
The USB-C port should be easily solvable with an USB-C to USB 5 cable adapter.
Try ESP32-S2 or ESP32-S3. It cheap and have 2.4 GHz Wi-Fi / Bluetooth .
https://www.espressif.com/en/products/socs/esp32-s2
https://www.espressif.com/en/products/socs/esp32-s3
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Interesting 
Could this be the proffieboard v4? ( all things great in 1 small package!)
ESP32 might be interesting, I will have to look into it.
It’s a fairly different environment, both programming-wise and hardware-wise, so it might not be easy to make it work.
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Looks like the S3 is the only one that is really suitable, since it supports SDIO, meaning that it can match the Proffieboard V3 in sd card read speed. The size of the chip + the external flash is going to make routing interesting though… At least if I want to keep the same size as existing Proffieboards.
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I think a longer board would not be the end of the world. Width is really the killer for narrow ID’s.
The CFX for instance, is 0.85" wide, and can be hard to fit in smaller hilts.
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Yeah, narrow width is one of the major pluses compared to rivals. You can fit this bad boy in way smaller spaces. (Title of your sex tape)
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The Technical Reference Manual is no light read. 26 pages of table of contents, ~847 total.
The STM32L433CCU6 (proffieboard V2) has a 1600 page reference manual, so yes, 847 pages sounds fairly light to me.
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Try mpu6500 or MPU6050 instead of LSM6DS3H, but mpu6500 is more expensive.
https://www.digikey.com/en/products/detail/tdk-invensense/MPU-6500/4385412
The mpu6500 in China just USD 1.57. LSM6DS3H is USD 8.6,LSM6DSM is USD 3.4.
mpu6500 cheaper in china.
If at all possible, I think I would like the next proffieboard to (V4) use a Risc-V cpu.
It’s the only truly open-source CPU architecture. Right now there isn’t a good option for this, but I’m hopeful that there will be lots of options for Risc-V CPUs available soon.
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Stupid idea of the day:
Since it seems difficult to find a good replacement processor for the proffieboard…
Maybe the solution is to have more than one? Two processors connected by a serial port or SPI or something. Not sure if it should be two of the same kind of processor, or if should be two different ones though.
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