I would want to initially leave the sequencer out, because that isn't really the "magic" part of this machine. Converting this project into a full-fledged SP1200 replacement wouldn't be a very difficult task (compared to the rest of the project). Add a GPIO expander or two off of the main microcontroller, and replace the MIDI input code with sequencer code. Leave the sample engine code the same. Booya.
Living sounds, the thing about the sampling part is that you would have to have 8 output channels for accurate output, even if you're only interested in playing one sound at a time. You'd probably also be limited in how far you could raise the sampling rate, as well. The reason is that all 8 channels were fed by a single multiplexed DAC. The short version is:
- One channel's 12 bits of sample data is fed to the DAC
- DAC feeds another 8-bit DAC to set sample level (first DAC's output is used as voltage reference, 8-bit sample data sets level)
- A capacitor holds the analog output of the level DAC for its channel (my apologies for bad terminology... electronics is not my forte)
- Capacitor feeds output stage
- Switch to next channel, repeat
If each channel's sampling rate was 26.04 khz, then the DAC would have to run at 8 x 26.04 = 208.32 khz
The sample clock seems to be several steps removed from the crystal, as well. It goes through a bunch of TI counter ICs and through a PAL IC. The clock would probably be difficult to reproduce without knowledge of how the PAL was programmed by E-mu.
I wish I never sold my SP12.
