[sdiy] MIDI HD

Michael Zacherl sdiy-mz01 at blauwurf.info
Fri Feb 15 23:50:46 CET 2013

Hi Tom, 

	thanks for your reply!

> If their coders were good, I'd want to see a much faster rate on the MIDI-over-USB connection than the old school DIN,
> but I bet they use the same data on both.

you're right, it's much likely the case that they just spared the extra code for utilising the speed of the USB connection.
After all it's a cheap box, either they didn't even think of it or they deliberately skipped that opportunity in order 
to keep the development cost down. Anyway, the result is the same.
On the contrary, with the Korg NanoKONTROL2 I mentioned, since it just has a USB-interface, the whole buffer/speed issue looks different.

> I completely agree that the 50Hz update rate makes the 14-bit accuracy useless for added smoothness. Often people don't realise this and think more resolution will help, but of course, unless the update rate is faster, all you're doing is defining the level of the steps more accurately!

It is possible to get those fine grained values on the BCF2000, I didn't manage to detect stepping by manually moving the faders.
So in fact the positional resolution is there, which, where I controlled a softsynth I wrote in SC3 with it, 
allows me to get much more detail of the controlled parameter than ever possible with 7 bits. But just slowly.

Of course there may be and are continuous parameters which don't necessarily demand that kind of high resolution, let alone switches, selectors etc.
And, from my POV, as a user of generic commercial control devices, it's an inherent problem that these generic devices can't cover all
the needs for an appropriate control of the corresponding parameter. And of course there are commercial limits.

OTOH with 14 bits the resolution is still not high enough to make other effects like value jitter irrelevant for the receiver,
(in terms of that the value change is small enough), _if_ it occurs. 
Something where the BCF isn't very good at either, it's pretty noisy and quite often keeps sending data without touching the faders. 
At last the boxes we have at the department do that. Maybe they are just old and messed up.

(just mentioning, I think I'm aware that I'm "preaching to the choir". ;-)

>> Dave Smith (he should know) says here 
>> <http://www.youtube.com/watch?v=buVeoLnL3tc&t=471>
>> quite something about MIDI, 


> Basically, what I think Dave S is saying is that they use plenty of digital filtering internally to smooth MIDI edits.
> It's quite possible to use a 7-bit MIDI value to alter a 16-bit parameter - just use the MIDI value to set the top 7 bits of the 16, for example. You'll get the full range, but you won't be able to get all the values over MIDI, but there's no problem there. The problem is the big jumps.

So in case of a sweep it's the same kind of prolem: there is some considerable stepping.
This is something, where I (almost literally ;-) could iron out the steps in my application I mentioned above:
The low update speed I could compensate to some extend by filtering on the receiver side.
The fine resolution end value was available. 

> So then you have to digitally filter your 16-bit values, to make sure that any DAC outputs pass through all intermediate values when someone does a MIDI knob twiddle. This requires both a faster data rate than MIDI and more resolution than MIDI - digital filtering can provide both of these,
> and *I think* that's what Dave was on about. 

Well, if I understand you correctly, you (and Dave Smith actually mentioned it) are referring to parameter sweeps.
Well, as he says in the video, "that's easy". But the grid of possible values is still there.
That's why I looked at the manuals of Dave Smith's own products to see how he/they solved this issue.
And he also mentioned his musical approach in the video, for instance by using semitones for the filter,
but which also causes audible stepping when swept. So that's a job for a smoothing stage.
But I couldn't find a fine tune parameter in his charts, which means e.g. in the case of filter modulation,
the selection of possible values still is limited.
But of course this also depends to a large extend on the whole layout of the structure of the synthesiser wether
that spoils the meal or not.

> Not doing that filtering and letting raw 0-127 value steps through to your final filter DAC *is* just sloppy,
> I definitely agree with him about that. No excuse for it!


cheers, Michael.

feed your perception: http://blauwurf.at

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