Sunday, 30 July 2017

Probably - an antidote to step sequencers...

I've always loved step sequencers. From the ARP Little Brother, to my own modular synths, 8 or 16 step notes metronomically repeated ad infinitum has always been part of my synthesis toolkit. But there's always been a tiny nagging voice whispering in my ear, and recently, I decided to listen to it and see where it took me. The voice told me to break the four rules:

The Rules of Step Sequencers

- Each step is one note.
- Each step has the same length note
- Each step has a find common velocity
- Each note always plays

So MIDI Probably gleefully breaks them! Each step in this M4L add-on can have from one to 13 pitches, spread over an octave. If you have one pitch, then the note played is that pitch. If you have two pitches, then each one will play, on average, for half the number of times that the sequencer loops round. Three notes get a third each. Four notes get a quarter, etc. Just probability really. There's a random number generator inside, and it decides which of the choices that are specified gets to control that note event.

There are four grids that are used to control Probably. From left to right they are:

Pitch, which is arranged paint roll style just like Live. Higher pitches are higher up the screen, lower pitches are lower down the screen. You get a black and white guide to show where the notes are. One octave may seem a bit limiting, but Probably accepts incoming MIDI notes as transpose settings, so you can transpose the playing sequence live with th computer keyboard, an external MIDI keyboard, or a session clip (if you make the session clip several bars long, then you get a transpose sequence that drives Probably...).

Probability, which sets the likelihood of a given step actually playing. The top row is 100%, where the note event always plays, whilst the lowest row is 0%, where the note event never happens. If you put a white square in the top row and the lowest row by clicking on the same step, then you get a 50% probability of that note event happening. If you replace those two square with one in the middle, then you get 50% as well. But if you add a lower square at 25%, then you get half of the notes playing for half of the time, plus a quarter of the notes playing for half of the time. If you have a square in the top, lower and 25%, then each gets a third of the time, which is 100% (33%), 0% (0%) and 25% (8.1%). Don't bother too much with trying to understand the maths: the more and higher the squares you fill in, the more likely it is that a note event will play.

Velocity, which sets the velocity for each note event. Again the top row is maximum velocity (127), and the lowest row is minimum velocity (1). Selecting specific squares gives fixed instances of velocity, whilst selecting a range of squares will give a range of velocities - each chosen at random. Single squares give fixed velocity. So you can have notes on the beat have fixed high velocity, whilst notes off the beat can have lower random velocities to add interest, or the opposite, or any other scheme you can think of.

Length, which sets he length of the note events. Each note event is independent, so if you want to have steps where the notes are longer than the step interval, then you can have them, and so you get chords instead of single notes. Each note can have its own length, and act length can be randomly chosen from a range or set of values. You control the values, and the randomness just make the choices.

If you've never played with a step sequencer that allows control over the length of notes (from staccato, to legato, to overlapping chords), or one where velocity is controlled random choices, the you are in for a treat!


When you add MIDI Probably to a track, then it starts up in a weird default:

This isn't very useful, and the first thing you need to do is compensate for my laziness in not writing the code to create a sensible default. Here's my suggested starting point:

This has a rising arpeggio for the Pitch grid, a top row full of 100% for the Probability grid, Maximum Velocity, and 16th demis for the Lengths. You need to provide a Pitch reference for the transpose, so arm the track, and play a note on the computer keyboard, on your external keyboard, or in a clip (which could be a slow, multi-bar transpose map for people who love circle of fifths etc.) Playing this gives a simple 8 step sequence:  

Well, nothing spectacular so far!

So let's draw in the opposite arpeggio:

Running this gives a rather more interesting result. You get each of the pairs of notes in each of the columns, selected at random. Every 16 bars or so, you stand a reasonable chance of getting all f the possible variations of each of the two arpeggios. Here's some of the output:

That word 'variations' is very significant here. Two notes have been specified for each of the 8 steps, and Probably dutifully selects at random from each of those pairs, and eventually will play every combination of the notes. The result sounds like someone learning jazz improvisation based on a scale, and most people assume that there's huge amounts of processing behind it... You might want to keep quiet that there's actually just a very simple grid, and probability does all the rest.

The red lower portion of those piano rolls shows the usual boring velocity values of 127, so lets put some ranges into the Velocity grid:

The first note in the arpeggio, plus the middle one, have single velocity values, so they will always play at maximum velocity. The remainder in the first half get quieter on average, and the second half hey get quieter still. There's still a chance that you will get all of the notes at the maximum velocity, but it might take a long time to get to it. Here's a capture:

Notice that the notes are different from the previous example. Not only re the velocity values being chosen according o the white squares for each note, but each note is independent, and so the sequence of jumping between two arpeggios that we got the first time, is different this time. This is randomness, not repetition.

Let's add a bit of control over the Probability, by making the off-beat notes less probable. (This is kind of emulating what real human players tend to do in some circumstances...) And the Length is now set to choose from a range of possibilities, but set exactly the same for each note event (painting across all of the columns is easy, but boring - I prefer the individual control against time that is shown in the probability and velocity grids). This gives us a sequence which has lots of variation across multiple parameters:

...and the result starts to look and sound quite interesting:

There's not very much range to the velocity or the length, so let's increase the amount of white squares and give it a few more pitches to play with:

Which gives us this output:

Now, does this look like a piano roll generated from a few simple choices on a few grids to you?

Lets try a different pair of arpeggios, and make those Lengths a little longer:

Resulting in:

Remember that this is produced by a step sequencer...

Instead of arpeggios, lets's constrain the choices to just a few notes from a scale, and see what happens:

 And let's try making the available note choices much sparser, and make the length of the notes (and the probability) dependent on where we are in the bar:

I'm afraid to say that when you add a piano instrument to the track, this gives results which sound pretty much like a reasonably competent player randomly noodling on the piano. All you need to do it capture it to a MIDI track, and then select the bits you like: either for inspiration, or just 'as is'.

To capture the output of Probably, you just create a new MIDI track, setts input to the output of the track with Probably on, and then use the Session Record button to create a new clip with the output of Probably. (I call the Session Record button the 'new doughnut', because it is a circle next to the 'NEW' button, and it goes red (I think of it as brown) when it is recording).


When you first insert Probably into a track, you need to provide a note. If you don't, then the transpose function will think you want to transpose way down at the bottom of the MIDI range. Because of the way that Probably works, you also lose the lowest C (C-2) from the output. Sorry. 

And that's MIDI Probably, a kind of 'antidote' to the usual M4L step sequencer. Enjoy playing with randomness!

As always, you can get MIDI Probably from


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