Digutal output on the G2, for CV control

dorremifasol

I think this has been discussed before but I'm not sure.

I was wondering if it could be possible to pick up a signal from a G2 output in digital form, and transform it into a digital stream. But that not would only be for audio, it could be used to bring some CV outs using multiplexing (4 for example at 24khz or even more, using only one output). I know this would need an additional device, but to me it would well worth any price! The possibilities (and sound quality) if the G2 would be greatly enhanced with additional analog modules controlled from inside.

What do you think about that?

ZeeByeZon · Posted: Fri Mar 30, 2012 2:14 am Post subject:

Don't you think it would be simpler to use MIDI out from the G2 with a MIDI to CV converter?

dorremifasol · Posted: Fri Mar 30, 2012 2:24 am Post subject:

Not at all. MIDI output of the G2 is very slow (very few hertz, and lots of jitter), and far from good to control CV in real time. Besides, only 7 bit is poor resolution.

With the method I'm proposing you could have up to 24 bits of resolution and modulation at audio rate for the CVs!

It came to my mind after seeing this device:

http://www.expert-sleepers.co.uk/es4.html

ZeeByeZon · Posted: Fri Mar 30, 2012 3:16 am Post subject:

OK get it.
With MIDI you can reach up to 1562Hz @ 14bit resolution (using PB or PAT). Jitter will appear when using several controls simultaneously.

What is really missing on the G2 is digital outputs (like spdif or ADAT)...
Multiplexing on analog outputs will probably lead to serious synchronization issues, and the high frequencies would probably be filtered out in the analog path, resulting in data distortion...

dorremifasol · Posted: Fri Mar 30, 2012 3:31 am Post subject:

Maybe I didn't explain it correctly. I meant getting the digital output signal from the DAC input, not from the analog output. I think it should be possible!

jksuperstar · Posted: Fri Mar 30, 2012 9:47 am Post subject:

I had looked into this a long time ago, and it is very possible. IIRC, the Nord uses Cirrus Logic DACs. The interface into those chips is well documented.

There are some gotchas: The Nord runs at 96kHz. That means S/MUX mode if using ADAT. OR, downconverting to 48kHz/44.1kHz, and doing normal ADAT.

It would be possible also to throw in an FPGA or something, or maybe just a little processor, and make an algorithm to demux CV signals that are multiplexed over audio. Maybe it'd tap into the MIDI I/O and one can control these new G2 digital outs from within a patch (to indicate 96/48kHz operation, how many CVs are multiplexed, etc).

So if everything went over ADAT, you can get
4 audio outs @ 96kHz
4 audio outs @ 48kHz
3 audio outs @ 48kHz, plus 5 CV outs (upsampled to 48kHz from 24kHz).
2 audio outs @ 48kHz, plus 6 CV outs.
1 audio outs @ 48kHz, plus 7 CV outs.

It's also possible to run at 44.1kHz with the same # of outputs.

There could be a breakout box for more CV signals...so add a second ADAT out, or just drill into your G2 and put it all in one box.

or any combination from there.

it would require soldering directly on the G2 motherboard to access these signals. It would also require some form of daughter board, and probably a small power supply (with partial sharing ground with the nord). I have no idea what the space is like in a G2 engine, but it's very doable in the G2 keyboards.

Also, we'd have to assume the G2 doesn't smear any data between the patch and the outputs. If multiplexing was to work, it would be necessary for the nord NOT to mess with the data from the patch. Which can't be fully possible, since there are 4 slots that need to be mixed before the final outputs. If it's *just* a volume adjustment per slot, that's ok. But if there's any filtering done, that will smear one CV's data into the next mid-stream.

I agree with you..the outputs are the weakest link of the audio chain in that box. 24 bit/96kHz through single ended -10db outs?! They should at least be balanced outs, AKM converters would've been better, and ADAT outs the best.

drapdap · Posted: Fri Mar 30, 2012 1:33 pm Post subject:

jksuperstar · Posted: Fri Mar 30, 2012 2:55 pm Post subject:

This post doesn't have anything to do with the original question, but relevant to the whole idea:

Ignoring the inputs (trying to do ADAT into the G2) makes the job much easier. I think the master word clock for the G2 is internal to the Freescale microprocessor used (used to manage the DSPs, all I/O, USB, and MIDI). That means it would be impossible to lock to another clock. Sampling from ADAT would mean going through an asynchronous sample rate translator, which is probably more work than really worthwhile, since you can't handle the digital very ideally, and also makes thigns nearly impossible to multiplex multiple CV signals into 1 input to the Nord.

Just an FYI for the overall idea.