10/14-bit midi discussion etc.

[lordmortis]

Hi - I'm relatively new to this MIDI stuff but I had a few questions about 10/14/whatever-bit precision midi controls

1) I'm wanting to build a midi controller for a VJ'ing application and I desire extra precision controllers because if I want to control an object's position on screen via midi - 800/127 = 6 pixels per midi unit, which isn't precise enough. with 14-bit midi i'd be able to go up to a resolution of 16384 before having a problem. (yes. a possible solution is to use rotary encoders.)

2) For DJ'ing apps, putting your pitch slider on a 7-bit midi slider is... non optimal. Again a 14-bit slider would be useful. Admittedly Traktor (my DJ program of choice) doesn't yet support this and i'm guessing the response will be "use a rotary encoder".

I realize that using rotary encoders solves a lot of these problems but they are no where near as "nice" to use as sliders/knobs etc. I'm also  aware there are jitter / etc problems when you try to use higher precision controllers but I was wanting to get some feedback/pick people's brains on their thoughts about 10/14/21/28 bit precision controllers (the last two being VERY non standard, but doable if you are writing the software on the other end. Though anything beyond 14 bit is overkill, and getting pots/sliders with that kind of precision would be quite difficult)

[stryd_one]

Well You've basically got 3 choices as far as how to send the message:

CC's - 7 bit. Fixed. It's in the spec.

(N)RPN's - 14 bit. Again, fixed, in the spec. Slightly slower, of course.

SysEx - Whatever you want. SLOW. Would defeat the purpose of fine bit depth by reducing frequency of changes to an unacceptable level.

Trick is that the PIC has 10 bit converters onboard, so you'd have to use external AD if you wanted to use an analog pot/slider at full 14 bit resolution. You could always just drop the 4 least significant bits, 1024 steps ain't so bad... Maybe you could emulate the effect on your PC, take a few bars of your favourite song, and reduce the volume to say 90%, and then 89.9%, see if you can tell the difference ;) OK now put it behind a compressor and some fx and a PA style brickwall limiter and see if you can spot the difference...

But if you just gotta gotta go digi, you've hinted that you don't want rotary controls but sliders. There are linear encoders, but you'd have to develop your own driver and I think they're hard to come by in the type you're after...

You could write code to use two sliders as a coarse and fine control, which would probably be OK or maybe even better for onscreen positioning, but would be sucky for xfades.

Or you could try a little gadget I've been working on if you want... You know what tank tracks look like (You know, those things that armoured vehicles have instead of tyres)?

/------------------------------\

|o                                        E|

\------------------------------/

Basically you take a length of rubber, and you make a little conveyor belt, wrap it around a pin and an encoder, voila... Takes some creativity and tools and a lot of patience. Some hints: The axles, including (the one attached to) the encoder, need to be fixed at both ends. Bearings are your friends. If you used to skateboard grab an old set and reoil them. Cogs with teeth and matching teeth on the belt are best, otherwise the encoder will slip in an unpredictable manner. Or else you could employ a method similar to a belt drive turntable where the spindles have a lip which grips the belt.

Another idea... some of us might remember a few weeks/months back talking about the position sensing LED matrix

Which one of these ideas is best will depend upon the situation... Personally, I'd go 10 bit and use a slider.

Anyone have any other ideas?

[moebius]

I'm interested how improved resolution would be used in the application side? This seems to be the MOST overlooked thing by "Laptop DJ"^tm generation of Midiboxers.

Moebius

[stryd_one]

"Laptop DJ"^tm generation

LOL

Yeh Moebius may make a very good point... I have absolutely no clue as I am doing my very best to rid myself of the PC for anything other than multitrack recording and sysex librarian duties.

So tell us, does your software support control methods other than CC's?

[Wild_Weasel]

Hi!

As far is I know traktor can only handle 7bit singnals.

It works ok for setting the pitch in a +/- 8% range (typical sl 1210 range).

This setup gives you 64 steps in each direction which equals 0.125 % pitch

0 + 0.125 * 64 = 8 (%)

0 - 0.125 * 64 = -8 (%)

This might not be as exact as for example Numark TTX-1 (which feature a display so I can tell) and are able so in/de-crease the

pitch in a 0.1% grid. [in my opinion technics suck in this aspect, but hey they are 25 years old]

I can't tell if there is a second digit internally but I guess not.

For finetuning I included a set of two pushbuttons on my traktor controller to increase or decrease the pitch in even smaller steps.

Rotary encoders will work for setting the pitch but you need to write a C programm which translates the encoder movements to up/ down midi singnals (you midibox needs to emulate push button hits for positive encoder rotation and negative and you need to assign two functions in traktor). Otherwise you would end with an 0-127 value which is not worse or better than the analog values coming from a pot.

See this thread for the code of my traktor box.

http://www.midibox.org/forum/index.php?topic=3852.0      ->page 2

I used the encoder trick for pitch bending in my box but this should also work for setting the pitch as well.

Regards WW

[lordmortis]

Well - for my VJ'ing app I can control how it inputs the data - so I was thinking of the original midi spec of MSB, LSB (though i'm guessing that's not going to be any faster than using NPRN?)

What sort of ADCs would you guys reccomend for 14-bit sampling?

As for Traktor - NI haven't responded to our queries about 14-bit midi support (or midi feedback support)....

[drin]

As for Traktor - NI haven't responded to our queries about 14-bit midi support (or midi feedback support)....

Based on the people I know inside NI the answers are 'no' and 'no'.

-drin

[stryd_one]

Take a hint dude ;)

[lordmortis]

<shrugs> it'd be nice for traktor but it's not critical.

If i wanted 14-bit sampling for my own app (either via Dual CC's or NPRNs) how would i go about getting the input end working?