コンテンツ
1.ソフトウェアバージョン
matlab2013b
2.理論的知識
このパートでは、主にMIDIオーディオ信号の主なファイル構造の特性を理解するための原則は含まれていません。MIDIファイルの主な構造は次のとおりです。
http://wenku.baidu.com/view/298f6f758e9951e79b8927fa.html
3.コアコード
function midi = readmidi(filename, rawbytes)
if (nargin<2)
rawbytes=0;
end
fid = fopen(filename);
[A count] = fread(fid,'uint8');
fclose(fid);
if (rawbytes) midi.rawbytes_all = A; end
if ~isequal(A(1:4)',[77 84 104 100]) % double('MThd')
error('File does not begin with header ID (MThd)');
end
header_len = decode_int(A(5:8));
if (header_len == 6)
else
error('Header length != 6 bytes.');
end
format = decode_int(A(9:10));
if (format==0 || format==1 || format==2)
midi.format = format;
else
error('Format does not equal 0,1,or 2');
end
num_tracks = decode_int(A(11:12));
if (format==0 && num_tracks~=1)
error('File is format 0, but num_tracks != 1');
end
time_unit = decode_int(A(13:14));
if (bitand(time_unit,2^15)==0)
midi.ticks_per_quarter_note = time_unit;
else
error('Header: SMPTE time format found - not currently supported');
end
if (rawbytes)
midi.rawbytes_header = A(1:14);
end
ctr = 15;
for i=1:num_tracks
if ~isequal(A(ctr:ctr+3)',[77 84 114 107]) % double('MTrk')
error(['Track ' num2str(i) ' does not begin with track ID=MTrk']);
end
ctr = ctr+4;
track_len = decode_int(A(ctr:ctr+3));
ctr = ctr+4;
% have track.rawbytes hold initial 8B also...
track_rawbytes{i} = A((ctr-8):(ctr+track_len-1));
if (rawbytes)
midi.track(i).rawbytes_header = A(ctr-8:ctr-1);
end
ctr = ctr+track_len;
end
for i=1:num_tracks
track = track_rawbytes{i};
if (rawbytes); midi.track(i).rawbytes = track; end
msgCtr = 1;
ctr=9; % first 8B were MTrk and length
while (ctr < length(track_rawbytes{i}))
clear currMsg;
currMsg.used_running_mode = 0;
% note:
% .used_running_mode is necessary only to
% be able to reconstruct a file _exactly_ from
% the 'midi' structure. this is helpful for
% debugging since write(read(filename)) can be
% tested for exact replication...
%
ctr_start_msg = ctr;
[deltatime,ctr] = decode_var_length(track, ctr);
% ?
%if (rawbytes)
% currMsg.rawbytes_deltatime = track(ctr_start_msg:ctr-1);
%end
% deltaime must be 1-4 bytes long.
% could check here...
% CHECK FOR META EVENTS ------------------------
% 'FF'
if track(ctr)==255
type = track(ctr+1);
ctr = ctr+2;
% get variable length 'length' field
[len,ctr] = decode_var_length(track, ctr);
% note: some meta events have pre-determined lengths...
% we could try verifiying they are correct here.
thedata = track(ctr:ctr+len-1);
chan = [];
ctr = ctr + len;
midimeta = 0;
else
midimeta = 1;
% MIDI EVENT ---------------------------
% check for running mode:
if (track(ctr)<128)
% make it re-do last command:
%ctr = ctr - 1;
%track(ctr) = last_byte;
currMsg.used_running_mode = 1;
B = last_byte;
nB = track(ctr); % ?
else
B = track(ctr);
nB = track(ctr+1);
ctr = ctr + 1;
end
% nibbles:
%B = track(ctr);
%nB = track(ctr+1);
Hn = bitshift(B,-4);
Ln = bitand(B,15);
chan = [];
msg_type = midi_msg_type(B,nB);
% DEBUG:
if (i==2)
if (msgCtr==1)
disp(msg_type);
end
end
switch msg_type
case 'channel_mode'
% UNSURE: if all channel mode messages have 2 data byes (?)
type = bitshift(Hn,4) + (nB-120+1);
thedata = track(ctr:ctr+1);
chan = Ln;
ctr = ctr + 2;
% ---- channel voice messages:
case 'channel_voice'
type = bitshift(Hn,4);
len = channel_voice_msg_len(type); % var length data:
thedata = track(ctr:ctr+len-1);
chan = Ln;
% DEBUG:
if (i==2)
if (msgCtr==1)
disp([999 Hn type])
end
end
ctr = ctr + len;
case 'sysex'
% UNSURE: do sysex events (F0-F7) have
% variable length 'length' field?
[len,ctr] = decode_var_length(track, ctr);
type = B;
thedata = track(ctr:ctr+len-1);
chan = [];
ctr = ctr + len;
case 'sys_realtime'
% UNSURE: I think these are all just one byte
type = B;
thedata = [];
chan = [];
end
last_byte = Ln + bitshift(Hn,4);
end % end midi event 'if'
currMsg.deltatime = deltatime;
currMsg.midimeta = midimeta;
currMsg.type = type;
currMsg.data = thedata;
currMsg.chan = chan;
if (rawbytes)
currMsg.rawbytes = track(ctr_start_msg:ctr-1);
end
midi.track(i).messages(msgCtr) = currMsg;
msgCtr = msgCtr + 1;
end % end loop over rawbytes
end % end loop over tracks
function val=decode_int(A)
val = 0;
for i=1:length(A)
val = val + bitshift(A(length(A)-i+1), 8*(i-1));
end
function len=channel_voice_msg_len(type)
if (type==128); len=2;
elseif (type==144); len=2;
elseif (type==160); len=2;
elseif (type==176); len=2;
elseif (type==192); len=1;
elseif (type==208); len=1;
elseif (type==224); len=2;
else
disp(type); error('bad channel voice message type');
end
%
% decode variable length field (often deltatime)
%
% return value and new position of pointer into 'bytes'
%
function [val,ptr] = decode_var_length(bytes, ptr)
keepgoing=1;
binarystring = '';
while (keepgoing)
% check MSB:
% if MSB=1, then delta-time continues into next byte...
if(~bitand(bytes(ptr),128))
keepgoing=0;
end
% keep appending last 7 bits from each byte in the deltatime:
binbyte = ['00000000' dec2base(bytes(ptr),2)];
binarystring = [binarystring binbyte(end-6:end)];
ptr=ptr+1;
end
val = base2dec(binarystring,2);
%
% Read first 2 bytes of msg and
% determine the type
% (most require only 1st byte)
%
% str is one of:
% 'channel_mode'
% 'channel_voice'
% 'sysex'
% 'sys_realtime'
%
function str=midi_msg_type(B,nB)
Hn = bitshift(B,-4);
Ln = bitand(B,7);
% ---- channel mode messages:
%if (Hn==11 && nB>=120 && nB<=127)
if (Hn==11 && nB>=122 && nB<=127)
str = 'channel_mode';
% ---- channel voice messages:
elseif (Hn>=8 && Hn<=14)
str = 'channel_voice';
% ---- sysex events:
elseif (Hn==15 && Ln>=0 && Ln<=7)
str = 'sysex';
% system real-time messages
elseif (Hn==15 && Ln>=8 && Ln<=15)
% UNSURE: how can you tell between 0xFF system real-time
% message and 0xFF meta event?
% (now, it will always be processed by meta)
str = 'sys_realtime';
else
% don't think it can get here...
error('bad midi message');
end
function [PR,t,nn] = piano_roll(Notes,vel,ts)
%
% Inputs:
% Notes: A 'notes' matrix as returned from midiInfo.m
% vel: (optional) if vel==1, set value to note velocity instead of 1. (default 0)
% ts: (optional) time step of one 'pixel' in seconds (default 0.01)
%
% Outputs:
% PR: PR(ni,ti): value at note index ni, time index ti
% t: t(ti): time value in seconds at time index ti
% nn: nn(ni): note number at note index ti
%
if nargin < 2
vel = 0;
end
if nargin < 3
ts = 0.01;
end
Nnotes = size(Notes,1);
n1 = round(Notes(:,5)/ts)+1;
n2 = round(Notes(:,6)/ts)+1;
if vel == 0
vals = ones(Nnotes,1);
else
vals = Notes(:,4); % velocity
end
for i=1:Nnotes
PR(Notes(i,3), n1(i):n2(i)) = vals(i);
end
% create quantized time axis:
t = linspace(0,max(Notes(:,6)),size(PR,2));
% note axis:
nn = min(Notes(:,3)):max(Notes(:,3));
% truncate to notes used:
PR = PR(nn,:);4.操作手順とシミュレーションの結論
5.参考文献
A03-11
6.完全なソースコードを入手する方法
方法1：WeChatまたはQQ経由でブロガーに連絡する
方法2：MATLAB / FPGAチュートリアルを購読し、チュートリアルケースと2つの完全なソースコードを無料で入手します