I need a more precise sine wave than I have at the moment, with a larger range than I can get from the DCO.
That gave me an excuse to go ahead and create the wavetable/PCM oscillator I've been thinking about - there's a slot on the digital board exactly for this.
My colleague Alexander used a PCM5102A DAC for his project, and after taking a closer look it seems this was the ideal choice for my oscillator as well. Even better, I realised I had a breakout board with that DAC already, from Aliexpress, so I could go right ahead and test it!
Here is my layout:
CLK: GND
BCLK: Teensy pin 21
LRCLK: Teensy pin 20
DATA: Teensy pin 7
NB: All data/clock pins have a 22Ohm resistor on them to slightly slow down the edges. This is both suggested by the teensy communit (100Ohm) and the breakout board (22Ohm).
The rest of the configuration pins are already taken care of on the breakout board, but in any case they are:
DEMP: GND (Deemphasis off)
XSMT: +Vpp (Soft mute: un-muted)
FMT: GND (I2S)
FLT: GND (normal latency) - I've made this configurable in my circuit
For the rest of the pins, see my schematic:
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| I've added two inverting gain op amps that brings the output up to +/-5V. FLT (filter latency) is configurable and can also be disconnected from the control pin by cutting the solder jumper. |
I've already implemented wavetable morphing, through any number of wavetables. I've added the four basic waveforms (sine/tri/saw/square) and converted the Prophet VS wavetables into a format that I can use. It sounds amazing!
Right now the oscillators are routed through the ext pot. I originally intended wavetable oscillator duty to be performed by the DCO circuits, so there's a switch between DCO and waveform after the waveshaper on the analog board.
Now I'm not so sure anymore. It would be nice to not use the ext route. Instead, wavetable-osc could be routed directly to the mixer, and to have separate volume control per osc. Instead of having one channel per wavetable oscillator I could let one channel go to each of the busses. I can mix the oscillators digitally instead, and have digital volume control of them.
This is much more flexible. I can use both DCOs and WT at the same time, or I can make them mutually exclusive in software. The only issue is that DCO and WT have to share the same panel pot, meaning we no longer get knob-per-function if both DCO and WT are available at the same time. Then again, this could also be configurable...
