Included are some very basic synthesis functions, which can easily be replaced by your own code. MIDI can be also be generated from note information you create within matlab: perhaps useful for audio transcription or algorithmic composition.
Here's an example of reading in the included file, jesu.mid. First, readmidi.m parses the file into messages and stores them in a matlab struct.
>> midi = readmidi('jesu.mid') midi = format: 0 ticks_per_quarter_note: 384 track: [1x1 struct]
midi2audio will synthesize this midi information to a waveform.
The default uses a simple FM synthesis technique.
This can then be written to a file, etc.
% synthesize with FM-synthesis. % (y = audio samples. Fs = sample rate. Here, uses default 44.1k.) [y,Fs] = midi2audio(midi); %% listen in matlab: soundsc(y, Fs); % FM-synth % There are two other very basic synth methods included: y = midi2audio(midi, Fs, 'sine'); soundsc(y,Fs); y = midi2audio(midi, Fs, 'saw'); soundsc(y,Fs); % save to file: % (normalize so as not clipped in writing to wav) y = .95.*y./max(abs(y)); wavwrite(y, Fs, 'out.wav');
To add or modify synthesis algorithms, you can change or replace the 'synth.m' file.
Internally, midi2audio uses the midiInfo function to generate start and end times of all notes in the file. midiInfo will display a list of the midi messages in the file:
>> midi = readmidi('jesu.mid');>> midiInfo(midi); -------------------------------------------------- Track 1 -------------------------------------------------- - 0 0:0.000 meta Set Tempo microsec per quarter note: 500000 - 0 0:0.000 meta Time Signature 4/2, clock ticks and notated 32nd notes=24/8 0 751 0:0.978 Note on nn=43 vel=99 0 171 0:1.201 Note on nn=67 vel=68 0 133 0:1.374 Note on nn=67 vel=0 0 29 0:1.411 Note on nn=69 vel=75 0 91 0:1.530 Note on nn=69 vel=0 . . .
midiInfo also returns a matrix of size Nx8, where N is the number of notes in the file. The 8 colunms indicate:
>> midi = readmidi('jesu.mid');>> Notes = midiInfo(midi,0);>> whos Notes Name Size Bytes Class Notes 90x8 5760 double array Grand total is 720 elements using 5760 bytes >> Notes(1:5,:) ans = 1.0000 0 43.0000 99.0000 0.9779 1.6120 3.0000 8.0000 1.0000 0 67.0000 68.0000 1.2005 1.3737 4.0000 5.0000 1.0000 0 69.0000 75.0000 1.4115 1.5299 6.0000 7.0000 1.0000 0 71.0000 88.0000 1.6250 1.8268 9.0000 12.0000 1.0000 0 55.0000 88.0000 1.6354 2.1979 10.0000 16.0000
This "Notes" matrix can easily be used to create a "piano-roll" display. I've included a script for this:
%% compute piano-roll: [PR,t,nn] = piano_roll(Notes); %% display piano-roll: figure; imagesc(t,nn,PR); axis xy; xlabel('time (sec)'); ylabel('note number'); %% also, can do piano-roll showing velocity: [PR,t,nn] = piano_roll(Notes,1); figure; imagesc(t,nn,PR); axis xy; xlabel('time (sec)'); ylabel('note number');
This results in:
writemidi.m and matrix2midi.m allow you generate some notes somehow in Matlab, and write them out to a MIDI file. Here's a simple example of creating a chromatic scale:
% initialize matrix: N = 13; % number of notes M = zeros(N,6); M(:,1) = 1; % all in track 1 M(:,2) = 1; % all in channel 1 M(:,3) = (60:72)'; % note numbers: one ocatave starting at middle C (60) M(:,4) = round(linspace(80,120,N))'; % lets have volume ramp up 80->120 M(:,5) = (.5:.5:6.5)'; % note on: notes start every .5 seconds M(:,6) = M(:,5) + .5; % note off: each note has duration .5 seconds midi_new = matrix2midi(M); writemidi(midi_new, 'testout.mid');
Note, you only have to specify the first 6 columns of the note matrix (7 and 8 hold the index of MIDI messages). Now, you should have a valid MIDI file to open elsewhere. If you're on Linux, you might have timidity installed,
$ timidity testout.mid # hopefully you hear something... # or convert to wave, and play with wave player: $ timidity -o testout.wav -Ow testout.mid $ aplay testout.wav
Now, let's try creating some random music: let's say 200 random notes with random start times and volumes, etc...
% initialize matrix: N = 200; M = zeros(N,6); M(:,1) = 1; % all in track 1 M(:,2) = 1; % all in channel 1 M(:,3) = 30 + round(60*rand(N,1)); % random note numbers M(:,4) = 60 + round(40*rand(N,1)); % random volumes M(:,5) = 10 * rand(N,1); M(:,6) = M(:,5) + .2 + rand(N,1); % random duration .2 -> 1.2 seconds midi_new = matrix2midi(M); writemidi(midi_new, 'testout2.mid');
This sounds much cooler with timidity's grand piano synth:
$ timidity testout2.mid
Congratulations! You're now a modern art composer.
These result in the following piano-rolls:
readmidishould be able to read any MIDI file - it does little parsing except breaking up into individual messages (handles deltatimes, running-mode, and determines the message type).
>> midi = readmidi('orig.mid',1); %% need to return rawbytes...>> isequal(midi.rawbytes_all, writemidi(midi,'new.mid'))
The files are hosted on github. The project includes these files:
|readmidi.m||reads MIDI file into a Matlab structure|
|midi2audio.m||convert the Matlab midi structure into an audio vector|
|midiInfo.m||display detailed information about MIDI Matlab structure|
|synth.m||synthesize a single note|
|getTempoChanges.m||finds times of all tempo changes|
|midi2freq.m||convert MIDI note number (0-127) to frequency in Hz|
|matrix2midi.m||create MIDI Matlab structure from a matrix with information on individual notes|
|writemidi.m||write a MIDI Matlab structure (such as created by readmidi) to a MIDI file|
There is more documentation within each
m-file. For example type,
help midi2audio in MATLAB.