I am about to start the design phase on 3 MIDI control surfaces, 2 decks and a mixer as part of my electrical engineering degree. The 2 decks will be built into the cases of turntables that I will get from ebay (can usually find some that have broken tonearms or no cartridge) maybe same deal with the mixer, although I will have to re-cut the front panel, basically there are a few technical bits I need to know.

First the dumb question: are all mixers a standard size, height wise? or depth for that matter? or are they all different sizes?

How many increments would one require around the circumfrence of a deck to be able to control the position of the track accuratly enough for accurate mixing, 1 degree? 0.1 degree?

What sample rate would be required for the deck? such is the nature of digital that the position of the deck has to be updated every time interval (be that whatever), it is unlikely that a high sample rate would be required for normal operation, but for scratching, how many times a second would the position of the platter need to be updated. (the sample rate of the platter does not affect the continuity of the track, the positions will be averaged.

What lag time between a movement of the platter, and the reponse of the track would become annoying? 100ms, 10ms?

Finally, how many increments of pitch control would be required? what do the high end CDJ's use? .01? Likewise with X-Fade, Gain, etc..

Sorry if these questions seem a little odd, but I'd rather hear it from the experts, before I build a deck that's inadaquet for anything more that a childrens toy.

http://homepage.ntlworld.com/p.sproson/decks.html

check this page for some info, its not the most technical but if you email him he has a degree in all that electronics stuff, plus hes a sound guy so he will help you

quote:

Originally posted by G`Dave First the dumb question: are all mixers a standard size, height wise? or depth for that matter?

not really, although 10" or 19" are standard widths but not all mixers comform to these!!

quote:

How many increments would one require around the circumfrence of a deck to be able to control the position of the track accuratly enough for accurate mixing, 1 degree? 0.1 degree?

not too sure on this one, when you mean control the track for accurate mixing do you mean cueing? If so then i guess it depends on the format of the music. I know CDs are split into mins:secs:frames and i think (someone correct me if im wrong) that you can only cue up to an accuracy of one frame. So in that case you would want 360/74 degree increments as there are 74 frames per second (or something along those lines)

EDIT: no you wouldnt, im talking rubbish. Id say 1 degree would be good, you dont want your increments to close together as cueing then becomes a reet pain in the arse. Is there going to be a dual CDJ/Vinyl type jobbie like the CDJ1000s?

quote:

What sample rate would be required for the deck? such is the nature of digital that the position of the deck has to be updated every time interval (be that whatever), it is unlikely that a high sample rate would be required for normal operation, but for scratching, how many times a second would the position of the platter need to be updated. (the sample rate of the platter does not affect the continuity of the track, the positions will be averaged.

this is another tricky one, i think it all depends on the limitations of your software. a freind of mine is doing a digital mixer for his project (im doing an electronics degree too ) and his DSP samples the crossfader at something ridiculous like 10KHz, which is possibly a little bit of overkill. What id advise is think how many times a second you could move your hand, then double it and thatd probs be your minimum sampling rate.

quote:

What lag time between a movement of the platter, and the reponse of the track would become annoying? 100ms, 10ms?

i dont know what the lag is on final scratch, cant find it on their website, but something similar to that.

quote:

Finally, how many increments of pitch control would be required? what do the high end CDJ's use? .01? Likewise with X-Fade, Gain, etc..

.01 is fine for the pitch control, although you'll definately need more accuracy for the gain and crossfader.

hope that answers some of your questions! wish id thought of summat like this to do for my project, sounds a lot more interesting that what im doing!!

Last edited by djdk on Mar-21-2005 at 12:14

No idea what kind of sample rate would be required but as for lag, you want to be in the <20 ms range (FS and SSL are ~10 ms). If scratching is not the main thing, then you will be able to get away with a much higher lag but I would try and stay below 100 ms.

___________________
"You can only drink 30 or 40 glasses of beer a day, no matter how rich you are." - Colonel Adolphus Busch

Major Johnson - February Progressive Mix

Download Other Mixes

quote:

Originally posted by djdk not too sure on this one, when you mean control the track for accurate mixing do you mean cueing?

Yeah sorry, that's what I meant to say, I'm not the best in the terminology department.

Well, if the track is cut into frames by the software.. then that makes the number of divisions around a platter easy to calculate. I'll just find out exactly how many frames there are, stands to reason.

Getting the pitch adjustment into .01 increments might be difficult, the MIDI interface supports a maximum resolution of 10bit, which translates to 1024 increments along the length of the slider, which is more like .02 if the range were to be +/- 10%

Lag won't be a problem, the software can scale the lag produced within itself, which must be taylored to the power of the computer running it, but within the interface itself, there is usually no more than 2ms of delay. And scratching is not a priority, just wanted the extra functionality.

quote:

Originally posted by djdk EDIT: no you wouldnt, im talking rubbish. Id say 1 degree would be good, you dont want your increments to close together as cueing then becomes a reet pain in the arse. Is there going to be a dual CDJ/Vinyl type jobbie like the CDJ1000s?

I can't see how increasing the resolution of the platter would make accurate cueing more difficult, I would have thought it easier to beat match that way were you able to have the time difference between the beats of the two tracks down to a smaller increment.

And on the last point, the project does not process any audio at all, its mearly a contol interface for Traktor, I want the interface to emulate a analogue vinyl turntable as closely as possible.

quote:

Originally posted by G`Dave I can't see how increasing the resolution of the platter would make accurate cueing more difficult, I would have thought it easier to beat match that way were you able to have the time difference between the beats of the two tracks down to a smaller increment. And on the last point, the project does not process any audio at all, its mearly a contol interface for Traktor, I want the interface to emulate a analogue vinyl turntable as closely as possible.

Im not sure I explained that very well. What I mean is if the resolution is too fine then when your cueing the track (finding your start point) then you have to be very very fine with your movements with the platter, which i find makes life more difficult.

And on the last point, I see what you mean, but i would suggest that you have a go on some CDJ1000s and see what im talking about, it might give you a better feel for what im rambling on about

Let us know how the project goes mate, sounds really interesting

quote:

Originally posted by djdk Let us know how the project goes mate, sounds really interesting

I agree,

Sounds like a real interesting (yet ambitious) project, would like to hear how you get on.

the best digital turntables out there have 0.02% pitch increments, so that should do you fine. i can mix quite well with 0.05%, but 0.02% increments do make it more pleasant.

make the mixer as "tall" as the decks and you'll be fine.

___________________
check out my guest mix for OndaSonora Podcast (aug.2009)

quote:

Originally posted by djdk Let us know how the project goes mate, sounds really interesting

quote:

Originally posted by CraSHer[UK] I agree, Sounds like a real interesting (yet ambitious) project, would like to hear how you get on.

Will do, I'll be documenting everything thoughly and plan to upload pictures of the finished product, and some from the construction phase (I could also send some technical shematics if anyone is game)

And djdk I think I know what you mean about the cueing now, but it couldn't be any harder than cueing with vinyl, technically a vinyl track has an infinite amount of increments.
(Well not really, considering you can't divide past an atom, but now I'm splitting hairs)

What uni are you at and what year are u?

Monash Uni - Clayton
2nd Year

Sounds like an interesting project. I'm a 2nd year electrical engineering and computer science major. So far we haven't don't anything that cool.

Also, check this out for the MIDI control surfaces http://www.ucapps.de/

___________________
-tom