In this section we will learn how to connect a MIDI controller to send events into Sonic Pi to control our synths and sounds. Go and grab a MIDI controller such as a keyboard or control surface and let’s get physical!
In order to get information from an external MIDI device into Sonic Pi we first need to connect it to our computer. Typically this will be via a USB connection, although older equipment will have a 5-pin DIN connector for which you’ll need hardware support for your computer (for example, some sound cards have MIDI DIN connectors). Once you’ve connected your device, launch Sonic Pi and take a look at the IO section of the Preferences panel. You should see your device listed there. If not, try hitting the ‘Reset MIDI’ button and see if it appears. If you’re still not seeing anything, the next thing to try is to consult your operating system’s MIDI config to see if it sees your device. Failing all that, feel free to ask questions in our friendly forums: https://in-thread.sonic-pi.net
Once your device is connected, Sonic Pi will automatically receive events. You can see for yourself by manipulating your MIDI device and looking at the cue logger in the bottom right of the application window below the log (if this isn’t visible go to Preferences->Editor->Show & Hide and enable the ‘Show cue log’ tickbox). You’ll see a stream of events such as:
/midi:nanokey2_keyboard:0:1/note_off [55, 64]
/midi:nanokey2_keyboard:0:1/note_on [53, 102]
/midi:nanokey2_keyboard:0:1/note_off [57, 64]
/midi:nanokey2_keyboard:0:1/note_off [53, 64]
/midi:nanokey2_keyboard:0:1/note_on [57, 87]
/midi:nanokey2_keyboard:0:1/note_on [55, 81]
/midi:nanokey2_keyboard:0:1/note_on [53, 96]
/midi:nanokey2_keyboard:0:1/note_off [55, 64]Once you can see a stream of messages like this, you’ve successfully connected your MIDI device. Congratulations, let’s see what we can do with it!
These events are broken into two sections. Firstly there’s the name of the event such as /midi:nanokey2_keyboard:0:1/note_on and secondly there’s the values of the event such as [18, 62]. Interestingly, these are the two things we need to store information in Time State. Sonic Pi automatically inserts incoming MIDI events into Time State. This means you can get the latest MIDI value and also sync waiting for the next MIDI value using everything we learned in section 10 of this tutorial.
Now we’ve connected a MIDI device, seen its events in the cue log and discovered that our knowledge of Time State is all we need to work with the events, we can now start having fun. Let’s build a simple MIDI piano:
live_loop :midi_piano do
note, velocity = sync "/midi:nanokey2_keyboard:0:1/note_on"
synth :piano, note: note
endThere’s a few things going on in the code above including some issues. Firstly, we have a simple live_loop which will repeat forever running the code between the do/end block. This was introduced in Section 9.2. Secondly, we’re calling sync to wait for the next matching Time State event. We use a string representing the MIDI message we’re looking for (which is the same as was displayed in the cue logger). Notice that this long string is provided to you by Sonic Pi’s autocompletion system, so you don’t have to type it all out by hand. In the log we saw that there were two values for each MIDI note on event, so we assign the result to two separate variables note and velocity. Finally we trigger the :piano synth passing our note.
Now, you try it. Type in the code above, replace the sync key with a string matching your specific MIDI device and hit Run. Hey presto, you have a working piano! However, you’ll probably notice a couple of problems: firstly all the notes are the same volume regardless of how hard you hit the keyboard. This can be easily fixed by using the velocity MIDI value and converting it to an amplitude. Given that MIDI has a range of 0->127, to convert this number to a value between 0->1 we just need to divide it by 127:
live_loop :midi_piano do
note, velocity = sync "/midi:nanokey2_keyboard:0:1/note_on"
synth :piano, note: note, amp: velocity / 127.0
endUpdate the code and hit Run again. Now the velocity of the keyboard is honoured. Next, let’s get rid of that pesky pause.
Before we can remove the pause, we need to know why it’s there. In order to keep all the synths and FX well-timed across a variety of differently capable CPUs, Sonic Pi schedules the audio in advance by 0.5s by default. (Note that this added latency can be configured via the fns set_sched_ahead_time! and use_sched_ahead_time). This 0.5s latency is being added to our :piano synth triggers as it is added to all synths triggered by Sonic Pi. Typically we really want this added latency as it means all synths will be well timed. However, this only makes sense for synths triggered by code using play and sleep. In this case, we’re actually triggering the :piano synth with our external MIDI device and therefore don’t want Sonic Pi to control the timing for us. We can turn off this latency with the command use_real_time which disables the latency for the current thread. This means you can use real time mode for live loops that have their timing controlled by syncing with external devices, and keep the default latency for all other live loops. Let’s see:
live_loop :midi_piano do
use_real_time
note, velocity = sync "/midi:nanokey2_keyboard:0:1/note_on"
synth :piano, note: note, amp: velocity / 127.0
endUpdate your code to match the code above and hit Run again. Now we have a low latency piano with variable velocity coded in just 5 lines. Wasn’t that easy!
Finally, as our MIDI events are going straight into the Time State, we can also use the get fn to retrieve the last seen value. This doesn’t block the current thread and returns nil if there’s no value to be found (which you can override by passing a default value - see the docs for get). Remember that you can call get in any thread at any time to see the latest matching Time State value. You can even use time_warp to jump back in time and call get to see past events…
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