Connect sapf to elixir with Midiex

Mix.install([
  {:music_build, github: "bwanab/music_build"},
  {:music_prims, github: "bwanab/music_prims"},
  {:midifile, github: "bwanab/elixir-midifile", force: true},
  {:better_weighted_random, "~> 0.1.0"},
  {:midiex, "~> 0.6.3"}
])

Section

In this book, we’re going to connect elixir to sapf.

first, create an output port

dork_port = Midiex.create_virtual_output("dork")

Now, in a terminal run sapf and execute the following command:

> midiStart

This should result in a list of midiports something like:

gMIDIClient 4457347

midi sources 1 destinations 1

MIDI Source 0 ‘dork’, ‘dork’ UID: 356092455

MIDI Destination 0 ‘FluidSynth virtual port (36417)’, ‘FluidSynth virtual port (36417)’ UID: -971557172

Now, again in the sapf session, given the above output:

> 356092455 0 midiConnectInput

Finally, set debug on in sapf

> 1 midiDebug

Midiex.send_msg(dork_port, IO.iodata_to_binary([144, 72, 114]))

In the sapf terminal, you should now see:

> midi note on 0 1 72 114

• the interpretation of this is 0 -> sourceIndex, 1 -> channel (1 based), 72 - note, 114 - velocity

Now, in sapf:

> 0 1 mlastkey > –> #[72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 72 …] > > 0 1 mlastkey1 > –> 72

Midiex.send_msg(dork_port, IO.iodata_to_binary([145, 72, 114]))

In sapf:

> midi note on 0 2 72 114

> 0 2 mlastkey1 –> 72

Now, let’s try a control message:

Midiex.send_msg(dork_port, IO.iodata_to_binary([176, 11, 80]))

In sapf:

> midi control 0 1 11 120

> 0 1 11 0 10 mctl1 > –> 9.44882

• the interpretation of the command is 0 -> sourceIndex, 1 -> channel (1 based), 11 -> the control message we’re interested in, 0, 10, the range that the value (120) is scaled to. Thus, 120 (the midi value received) / 127 =~ 0.944882.

120 / 127

nnhz is the function that translates a midi note to a hertz signal.

in sapf:

> 0 1 mlastkey nnhz 0 sinosc .3 * play

Now, send it a note.

Midiex.send_msg(dork_port, IO.iodata_to_binary([144, 72, 114]))

You should hear the note. Send another:

Midiex.send_msg(dork_port, IO.iodata_to_binary([144, 60, 50]))

The note you hear should now be lower.

Likewise, one can detect velocity with mlastvel which works like mctl:

> 0 1 0 1 mlastvel

• the interpretation is 0 –> sourceIndex, 1 –> channel, 0, 1 –> the range that the midi velocity value will be scaled to. Thus, we might have:

• In sapf:

> 0 1 mlastkey nnhz 0 sinosc 0 1 0 1 mlastvel * play

Send a note at a given velocity.

Midiex.send_msg(dork_port, IO.iodata_to_binary([144, 60, 50]))

Now, change the velocity:

Midiex.send_msg(dork_port, IO.iodata_to_binary([144, 60, 30]))

Now, the sound should be lower.

Midiex.send_msg(dork_port, IO.iodata_to_binary([144, 60, 1]))

Now, it is effective off, even though sending a new velocity would show that it’s still running, just very low volume.

Now, let’s try something really crazy.