An idea I've toyed with involves making another audio adaptor board, specifically for people building Eurorack modules. If this ever happens, which is a pretty big "if", a realistic time frame would likely be early 2017. After the 180 MHz Teensy is released, and after the audio lib gets a granular synthesis engine and wavetables and more effects and more signal-modulated features, this sort of thing might make more sense (where "sense" means maybe enough of market... maybe?)
Such a module would have two SGTL5000 chips, with 4 DC coupled inputs and 4 DC coupled outputs. All 8 would be capable of +/- 10V signal range, or 8V or 5V, software configurable using the adjustable line-level in/out of the SGTL5000. Lower ranges like +/- 2.5V would need to be done in software, using only a portion of the hardware's analog range. Unipolar CV would just use the positive half. Of course, all 8 signals would have the full 16 bit, 44.1 kHz audio sampling and integrate with the audio library data flows.
I'd probably put a tiny EEPROM chip on the board. During testing here at PJRC, we'd do a room temperature characterization of the DC offsets and maybe also the exact signal gain. These would take into account both SGTL5000 level and resistors & offset voltages/currents in the opamp circuits. For applications that need to get very low DC offset voltage and precise signal levels, that info could be read and used for software-based correction.
It would probably also have a place to solder a 10 pin Eurorack power header, and it'd have a 12V to 3.3V step-down power supply to power the Teensy and codec chips. Filtered, reverse polarity protected +/- 12V would be passed through the pins to allow the rest of the module to get its power.
This wouldn't be a complete Eurorack module board. The idea is it's be a component used in one. It'd be the same 0.7 inch wide as Teensy, and probably 1.2 to 1.5 inches long. It and a Teensy would fit onto the back side of another board or stack of boards that provide the user interface, plus any other signal inputs or outputs.
Realistically, such an audio board would retail around $20 to $25. Together with a Teensy, that's about $40 to $50 for the DSP analog I/O infrastructure on the back layer of a module. By the time another board, pots, buttons, front panel and other stuff are added, it's not such a cheap way to make a Eurorack module. But maybe it'd be worthwhile, for the many DIY possibilities it might open up?
I know several Eurorack module builders are here, and please feel free to link to this thread from forums like MuffWiggler. I'm curious to hear any feedback. But please remember, this is only hypothetical so far, and if it does ever happen, the earliest likely timeframe would be in 2017.
