I thought that all of the effects boxes used DSP chips (and not uC or phone SoC chips)? Do you know what they use? Why aren’t you using that?
I don’t know about DSP chips - I’ve read some chip names in the past Sharc,Sharc2,Blackfin) but never paid any attention - they are more for bulk purchase and assmembly than diy home brew stuff - but I guess they have high speed floating point multiple and add and maybe some trancendentals (sin,cos,atan.tanh,pow e.t.c). But my initial tests with the PI Zero puts it’s 64bit floating point performance around 160million instructions per second. Which is bags of power for a £4.50 device - I suspect nothing else could compete with that power at that price point.
What do all of the nearly free clip-on tuners use for processing?
No idea! - I don’t have one, I do have a Zoom G1on - which has a tuner - which is terribly slow, a few seconds to lock onto the pitch. I suspect the cheap tuners use the naive approach - boost the signal and clip into a square wave then count the zero crossings and average over time to get rid of any harmonics e.t.c Probably using a simple PIC and Distortion circuit.
Why are you using C#/Unity vs. C?
C# for testing algos - It took me 1hr to knock up a simple unity app to test that arduino code. I can port to C/C++ very quickly (these algos are tiny so it’s a matter of a min or two). The turn around time from editing code to running it is super quick - about 2 secs. The turnaround time for a PI Zero is compile,copy to sd card - sd card in device - power it up (you can setup the pi to use a usb uart - but I’ve not done that yet). Turnaround time for arduino- I don’t know because mine has not arrived yet - it’s in the post - but it looks like - compile code - flash arduino chip with usb cable and power it up.
Why do you need a sound card, don’t the common audio DSP chips come with A/D and D/A?
Pi Zero only has HDMI audio output and no ADC’s. I’m bare metal coding using the awesome Circle libs (https://github.com/rsta2/circle) and not using HDMI, just I2C and SPI for oled/lcd display. So I found a simple audio board that does 96khz audio out and in for £16.50.
So many questions but I like your project, very cool!
I’m having serious fun developing it all
Oh, and what algorithm does a TC PolyTune use?
No idea - I did see a youtube vid with one of the developers/marketing guys at TC saying the Polytune had the longest R&D cycle in the history of TC products I do plan to do polyphonic tracking later - for various things(EHX Mel9 !!!). But honestly I don’t know how to do it robustly. My Guess would be FFT->Spectrogram->Auto-correlation to find the harmonic matches! I will research that at a later date.