I'm still beavering away at this - having fun! I've upgraded to using the Teensy 3.6, which has more processing power, and a whopping 256k or ram, which gives me around 3 seconds of audio at 12-bit. I’m using the PCB board I designed for my AudioFreeze project which was designed for Teensy 3.2. The 3.6 is twice the length, but by crafting a tower block of female header (well 2), I was able to raise the Teensy over the height of the ribbon power connector!
With all the extra processing power the 3.6 provides I was able to create 3 separate play heads, all looping audio at different pitches which is mixed together. One plays at 1/2 speed (1 octave down), one at normal speed, and one at double speed (1 octave up). Currently the mix ratios of these are fixed as I’ve run out of knobs on my board!
Here’s a very simple demo, you can hear the acoustic sound of the guitar in this video, normally I’d want the effect to be totally wet, but it does serve to show you what the original audio is doing..
I think I'm definitely getting closer to @dspk 's video that I originally cited. Next step is to add more pots to control all the parameters, and potentially add CV control for them all. I'd like to move away from using the audio shield, as I'm not really taking advantage of the 16-bit DACs/ADCs. I'm really only using it so I can use the Teensy ADC to read the pots. I'm planning on designing a new PCB and using a PIC chip to handle all of the pots and CV interface stuff and then connect that to the Teensy via I2C, but I've no experience of that, so that's a whole new adventure!