Xx review: algorithmic Midi composition from the makers of Metasynth

U&I software, makers of ‘Metasynth’ electronic music studio, have released an updated version of their algorithmic compositional software Xx. The software U&I make is standout from the regular crowd – much of their software combines many unusual ways of manipulating sound with graphics (Such as using photos to filter the source sound). They’ve continued in those paradigm-breaking footsteps, with the updated software Xx – an algorithmic midi composing tool.

Xx is a 24-track midi sequencer designed to generate and transform midi within (or beyond) the boundaries of compositional rules that you set. The software is a one-window affair, for simplicity. Most of the GUI is taken up by a piano roll – a familiar sight to anyone who’s used a DAW. There are 3 surrounding areas containing all the necessary tools to create and store midi. You can import midi tracks into Xx, and also create midi tracks within the program and export them as midi to your DAW, then render them to audio using the built-in synth or any AU plugin software you want to use.

Straight away, the available methods of inputting midi information take Xx far beyond any regular DAW piano-roll. The expected methods are there – step entry, single note entry, direct keyboard entry. But then it gets creative. Think of it a little like paintbrush-style buttons providing multiple ways to affect photos – it’s similar here, but with midi information. There’s brush strokes, one-click pattern entry, Chord entry, canon entry (what you enter is repeated 2 more times on different midi channels at a user-defined interval and time later), all the way to complete random note entry. The pattern tool button is excellent: as you write and create midi patterns, it is possible to store them in a pattern library, ready for easy access and use later. Xx remembers all the relevant information about the pattern – key, tempo, scale info etc. One click, and the entire pattern library is at your fingertips. You can input entire phrases with one click. Xx doesn’t come with too many patterns, and none of them are very inspirational. But it’s very easy to create and store your own patterns, quickly building a large library.

The toolbar above the piano roll generally deals with the midi channel selection, and the routing you choose for the sound you want. You can work on the 24 tracks simultaneously – differentiating between each midi track by colour, choosing whichever midi track you want to work on by simply selecting the appropriate coloured box in the toolbar. In terms of sound you want to use for reference, there is a built-in general midi synth for easy use, but the preferable option (at least for me) was use my AU plugins already on the computer as the sound source. There’s no set up necessary – Xx finds the plugins automatically at startup. You can use Plugin multis – so if, for example you’re writing orchestral stuff, and you want to use Kontakt as your source for 16 channels, you can set it up easily in Xx, and have a full orchestra playing in seconds. The only slight downside I found here is that if you do decide to use your AU plugins with Xx, it greatly lengthens the software startup load time. If you have the ‘use AU plugins’ preference button unchecked, the software loads in seconds.

So getting Midi information on to the piano roll is already pushing creative boundaries, as there are a myriad of different ways to do it. Once the midi is on the page however, Xx gets interesting. Using the powerful algorithms under the hood, it can take the midi that you’ve just written down, and for lack of better terminology, evolve it musically into new directions that you may not have thought of. All with minimal clicks. U&I write that a lot of users complement the DAW that they work mainly in with Xx, importing midi tracks to explore compositionally in XX and then export back out to the project they’re working on, which makes a lot of sense.

The algorithms analyse the midi tracks, and take into account various different parameters of the midi, such as key, tempo, scale type, time etc, before then suggesting, or generating further phrases to follow on from musically what is already there, letting the music develop thematically. There are several options under the ‘pattern’ menu (not to be confused with the pattern creation button) that guide the software to generate new material that is useful to the composition. Here are some of them:


This is a box that enables you to constrain any of the midi material you select to a specific user-defined, or preset scale. There are 15 preset scales, major, minor, arabic, modern(?) dodecaphonic, and so on. If none of these work, you can define each note of the scale. So the options are limitless. And the software will neatly move the midi notes around to fit within whatever scale you define.


Randomises everything. You get to choose and limit what is randomised – Notes, velocity, time, and duration, by however many notes or ticks, and by percentage of probability. So you can move from subtle change to wildness.


The Multi-transform box will take the midi phrase that’s been input, and repeat it, changing it ‘musically’ according to rules that you set for it. There are four rules you can set each time you transform, each with 9 parameters to change, from harmonic and chromatic transposition, to invert pitch, reverse time, to speed up and slow down. You can set how many times it should repeat, whether it should repeat every time, every other time, etc. Thus technically creating flowing, modulating phrases that go to new areas harmonically that you might not explore yourself.


This box is a sequence generator, that creates 3 midi sequences on separate tracks at once. It is a step sequencer, with 3 windows of note generation and 3 of velocity. There are many options to create and change the sequences here; you can choose how many steps each sequence has, independently, thus creating very complex polyrhythms if you want. You can reverse, shift, invert, reflect and mirror the steps, to name but a few options. There are also randomisation elements for every parameter. Then when you’ve finished creating, you can preview the sequence before you print to the piano roll.

The combination of these different tools means you can really take your midi patterns in directions that you didn’t expect, but that still make sense musically. Here’s a quick video showing how simple it is to create usable phrases from simple midi patterns:


I just covered the basic elements of the software – it goes much deeper than this review will allow, and is worth spending time with. I would highly recommend this program as a tool to aid with the pushing of your composition skill. If you’re running out of harmonic ideas, or just want to explore a melodic theme, this is a really good way of quickly coming up with variations and alternatives that have musical relevance.

I had a few thoughts about it that I would love to see to improve the software, and it’s intergration into my work process – I’d love to see it as an AU or VST plugin in itself – something that you can work directly within a DAW with – so you could explore compositional process without having to export, and import from one program to another. It would speed the process up dramatically I think. Also, there was only one level of undo. Having got used to Undo history, and unlimited levels of undo, I kept finding myself hitting apple z, and waiting for something to happen that never did. That got frustrating.

I think that Xx really lends itself to more classical-style composition – note the canonisation of melody, and scale and modulation options all pointing to a more traditional harmonic focus. However it would be short-sighted to say that this software couldn’t be used in any genre really – the pattern function can create really excellent arpeggiation patterns that can be subtly changed bar to bar to create really excellent evolving synth arpeggios, the multi generator can be used to create complex beats, and subtle movement around that. The software’s only really limited by your imagination.


… If you’re running out of harmonic ideas, or just want to explore a melodic theme, this is a really good way of quickly coming up with variations and alternatives that have musical relevance. …

Product page


  • Very quickly create fresh ideas on source material
  • Great price for what it does
  • Direct link to your plugins


  • If you’re into your midi composition, this is a very valuable tool for you. If you spend more time in the straight up audio realm, you won’t get much love from it.


  • learning curve fairly steep
  • Limited Undo function
  • Long load up time (if you want to use your plugins)

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