Friday, 29 November 2019

Off-Grid (as near as I can) extension to MaxForLive Probability MIDI Device

Sometimes a quick comment can trigger something much bigger. When I wrote about the Ableton Live Piano Roll editor for the MIDIprodD4 blog post, I mentioned that the piano roll had a not-so-well-known shortcut (the 'zero' key) for disabling notes...

This got me thinking, and there's another slightly obscure feature in the piano roll editor that got me thinking and then coding... So let's look at the shortcut first. If you have some notes on the piano roll grid, then you can move them backwards and forwards in time (clip limits permitting!) using the left and right arrow keys on the qwerty keyboard. The movement follows the quantisation setting, so if you have the quantisation set to 16th notes, then the notes can be shuttled back and forth in 16th notes.

Moving the snare to the right (time delay) by a 16th note, so that it is no longer aligned with the kick drum.
However, if you turn off the quantisation, then you can shuttle the notes back and forth (left and right) without the jumps being quantised to specific note lengths. This give you very fine control over the timing sloppiness.


But, after having moved a note (or several notes),  if you then put the quantisation back on again, when you use the arrow keys to move the notes left and right, something very interesting happens!


The notes don't do what you expect. Instead, they jump first to the quantisation places for the grid, so they are aligned as you would expect, but the second arrow key press moves the note by the amount that you set when quantisation was off! The next arrow press goes back onto the grid, and the next arrow press goes off it again, so if you had moved by a 128th note then the quantisation was off, when it is back on again, then the arrows move it by one 128th note, then a 16th minus one 128th note, then one 28th note, then a 16th minus one 128th note, etc. Once you know what it is doing, it makes perfect sense and is very useful.

Quantisation set to 16th note, Snare is on grid.

Quantisation set to 16th note, Left arrow key = Snare is off grid by one 128th note

Left arrow key = Snare is back on grid again, one 16th note later...

Left arrow key gain = Snare note is off grid again by one 128th note...

Here's another way of looking at what it is doing. Imagine you move a note by a 128th note when quantisation is off, so each arrow press moves the note by an amount of time that I'm going to call an O (for 128th) time period. Then when you put the quantisation on set to 16th notes, the arrow keys will move the note by S (a 17th note amount of time), then O, then S, then O.

I'm not sure if this is a feature or a bug, but it is very intuitive and very useful, and it got me thinking.. Maybe probability isn't the only thing that could be controlled between the clip piano roll and the Drum Rack?

MIDIoffGRID4


MIDIoffGRID4 is the result of that thinking, plus quite a lot of coding. It takes the basic idea behind MIDIprobD4, and extends it so that you get sophisticated control of the time delay of four specific drum notes (or ordinary notes, if you prefer to try it with synths and samples). The control isn't just fixed as the probabilities are in MIDIprobD4 (Ooh - now there's anther idea! Give me a few days!), instead it is dynamic, so each time a note is delayed it can be different (or the same, if you prefer), or it can be changed using an unusual kind of LFO (That I haven't seen used much either, which is another idea you may see soon - time willing!). Oh, and then at the end, you get control over the probability of the delayed notes happening. If these two devices were simulations, then MIDIprobD4 would be an unreliable drummer, whilst MIDIoffGRID4 would be an unreliable drummer with poor timing. Not that there are any drummers like this, of course!

In short, MIDIoffGRID4 lets you shuffle specific notes to the right (and then back to the left) without needing to open the piano roll and turn the quantisation off and use the arrow keys or dragging the notes sideways. And it lets you automate how much the notes are delayed. And it lets you control the probability of a note happening - which is pretty awkward to do in the piano roll (there are ways, but they can be ugly).


So, delay first. The screenshot above shows a setting of 52 128ths note 'ticks' for the time delay for Note 38 - the Snare drum. The 'Random' rotary control is set to 4 (by accident), but it isn't having any effect on the large white 'Delay Time' number on the right - that shows 52. This is because the 'Delay' rotary control goes straight into the 'Delay Time' display that affects the note timing, whilst all of the other three rotary controls (Random, Count, and Multiply) are affected by the 'Limit' rotary control (of which more in a moment), and this is set to zero. In a future update, I will try to remember to change the colours so that this is more obvious!

Anyway, the Snare has been made slightly late, so it doesn't exactly coincide with the Kick any longer, and so we get a sloppy second beat...


Here's no 'Delay', but the same value set on the 'Random' rotary control. This time the 'Limit' control is set to 52 as well, and so it will 'limit' the value of the previous three rotary controls to a maximum of 52, but it wraps round, so a value of 53 will be 1, 54 will be 2, etc. Technically, it is a modulus limiter. The 52 value for the 'Random' rotary control means that it will output values from 0 to 52, and so the value of 23 that is shown in the large white 'Delay Time' number is just a random value between 0 and 52. If the 'Delay' rotary control had been set to 10, for example, then this would be added in to the 'Random' value, and the 'Delay Time' large white number would show 33 in this case.

So now the Snare is variably late after the Kick! Sometimes it will be in time, and sometimes it will be slightly late, and sometimes it will be very late...


Here's the 'LFO'-type effect in operation. The 'Count' rotary control sets the maximum value of a counter that increments each time a drum note happens in the channel. In this case, the count will start at zero and go up to 104, then it will return to zero and count up again. The 'Multiply' rotary control affects the count as the name suggests: a setting of 1 should mean that the count goes 0, 1, 2, 3, 4, 5... etc. But a programming bug means that it actually goes up in 2s! So it counts 0, 2, 4, 6, 8, etc. A setting of 2 counts up in 4s, 3 counts in 6s, etc. I quite like that it does it wrong! But the 'Limit' is set to 52, so when the counter gets to 54, the delay time that is sow in large white numbers is 2 again. In other words, by setting the Count, Multiply and Limit rotary controls, you can control how the delay time changes, from slow increments of 2 ticks, up to complex repeating patterns caused y the modulus limiter.

In this case, the Snare gradually lags further and further behind the Kick, until eventually it resets and is in time again, but then it starts to lag behind again.

The 'Count' 'LFO-type effect is not easy as first to get your head around, but if you treat it like a synth and just noodle with the controls until you get a good sound, then you are following a process that has served generations of synth players very well for decades!

Oh, yes, and the 'Quantise' control lets you quantise the 'Delay Time' for each channel, although this isn't shown in the display... The default setting of 128th note 'ticks' is as unquantised as I could make it using the standard Max 'pipe' object - but see below for more thoughts on this.

Assigning channels to drums is up to you. You might want to not change the Kick drum timing, or there again, you might want to! For synths, then you could adjust the timing of four separate notes using a single instance of MIDIoffGRID4, whilst an Effect rack with multiple instances could give you control over many notes. Strums are one obvious application, but I'm sure you have wilder imaginations than that! Especially on Black Friday!

MIDIoffGRID4 gives you four channels of drums that can be time delayed in various ways, plus the final probability control. I'm hoping that this will result in some very interestingly time-varying and unpredictable drum tracks!

Oh, yes, and a liitle glitch during development means that some of the screenshots have this device shown as MIDIprob4, instead of MIDIoffGRID4. Sorry - I'm not a very disciplined programmer these days! 

Inside...

The Max / MaxForLive code inside MIDIoffGRID4 uses the same redundant Note On/Off 'Velocity of zero' approach as MIDIprobD4, but the way that I have delayed the MIDI notes and velocities is slightly left-field... Here's the essential bits of the code:

The left hand side has the MIDI note selection, which is done with a 'routepass' object that just routes the specific note to one output, and all other notes to another output. (Note that the split of MIDI note events into a stream of note numbers and a stream of velocities happens before this - outside of this code snippet.) The 'specific MIDI note' is set by a MIDI note number from the 'Selected MIDI Note' input - just a rotary control with a range of 0-127. I did debate as to whether I should restrict the range to something more appropriate to the conventional GM MIDI drum note number range, but decided to leave the range at its full extent so that non-drum events could be processed. I haven't explored the possibilities with synths and samples very much yet, and as with my Drum Flammer, I suspect that repeats and time delays on individual notes may be a bit unexplored, unpopular, unfashionable - which sounds like fertile territory to me...

The middle section contains two 'pipe' objects to delay the note stream and the velocity stream. The Help file and Reference for 'pipe' show the Cycling '74 thinking on how to use it - you send the packed stream of note and velocities thru the 'pipe' object. But I was thinking that it might be interesting to put different delays on the two streams, and so I split the 'pipe' into two, so there's a chance that a forthcoming MIDIoffGRIDpro might explore this in more depth.

The 'quantize' message to 'pipe' is interesting. There isn't a 'quantize off' message, and so the smallest time interval that you can set the pipe quantisation to is one 128th note. So this sets the 'tick' of MIDIoffGRID4's processing. I might try playing with a sample-rate version of 'pipe' in Gen to see if there's scope for shorter notes, but in order to work out if that is worthwhile then we need to consider the 'not-talked-about-very-often' MIDI transmission rate limit - oh dear, it looks like I'm talking about it...

MIDI Transmission Rate Limit

MIDI's serial connection is at 31.25 kbaud per second ('bits per second' in this context), and a minimalistic MIDI Note On and Off message takes 4 MIDI 'bytes' (2 for On and 2 for Off) when Running Status is active, so that's 31, 250 divided by 8 (to get it into 'bytes', and then divided by 4 to end up with messages, which gives an absolute maximum rate of 976.5625 messages per second. Now with serial communications, then limits like 'absolute maximum rate' are not something you want to be too close to...especially since a real-world MIDI data stream will probably have more than just MIDI Note On and Off messages in it ((MIDI Clock, Active Sensing, Controllers, etc.). For more typical 'in-stream' three byte MIDI Note On and Off messages then that second division is by 6, which gives  651.04166... messages per second.

To put these numbers in context, they need to be expressed relative to tempo and note lengths. I'm a 120 bpm sort of person, so 120 beats in a minute is 120 beats in 60 seconds, which is 2 beats per second, or 1 one beat every half second. For 4/4, then 4 beats per bar, so a quarter note is going to last half a second. From the previous calculations, we know that in that half second we could have just slightly over 651 MIDI note messages - which seems like quite a lot, and reflects the sort of engineering thinking that the original MIDI designers must have considered carefully. So a quarter note is one out of those 651 possible MIDI note messages, and so an 8th note would be one out of just over 325 MIDI note messages. A 16th note would be one out of just over 162 note messages, a 32nd note would be one out of just over 81 note messages, a 64th note would be one out of just over 40 note messages, and a 128th note would be one out of just over 20 note messages (and takes 1/64th of a second, which is 15 milliseconds). Now, depending on your medical source, 10 milliseconds seems to be somewhere near the middle of the measured range of the perception limit of human timing, and we are at similar amount of time with 128th note quantisation...

Gen into the pipeline?

So the calculations suggest that it might be worth looking into a Gen version of 'pipe' to see if using one 256th note quantisation (or finer) can be perceived, but only just. So I'm going to add this to the pipeline, but not with a huge urgency, and when I have a spare moment... Until then, I would be interested, as always, in any feedback from users of MIDIoffGRID4 about the timing resolution of one 128th note for the quantisation.

Getting MIDIoffGRID4

You can get MIDIoffGRID4 here (it is free!):

     https://maxforlive.com/library/device/5846/midioffgrid4

Here are the instructions for what to do with the .amxd file that you download from MaxforLive.com:

     https://synthesizerwriter.blogspot.co.uk/2017/12/where-do-i-put-downloaded-amxd.html

(In Live 10, you can also just double-click on the .amxd file, but this puts the device in the same folder as all of the factory devices...)

Oh, yes, and sometimes last-minute fixes do get added, which is why sometimes a blog post is behind the version number of MaxForLive.com...

Modular Equivalents

In terms of basic modular equivalents, then MIDIoffGRID4 would probably require four delays, four LFOs, eight Random Noise Generators and four Utility modules to do the Limit modulus function, plus a quad MIDI Utility module to do the velocity multiplying, giving a total of about 24 ME (without all the stored memories, of course).

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