1.软件版本

matlab2013b

2.理论知识

这个部分，不涉及什么原理，主要是对MIDI音频信号需要了解其主要的文件结构特点，MIDI文件的主要结构如下：

http://wenku.baidu.com/view/298f6f758e9951e79b8927fa.html

3.核心代码

function midi = readmidi(filename, rawbytes)if (nargin<2)rawbytes=0;
endfid = fopen(filename);
[A count] = fread(fid,'uint8');
fclose(fid);if (rawbytes) midi.rawbytes_all = A; endif ~isequal(A(1:4)',[77 84 104 100])  % double('MThd')error('File does not begin with header ID (MThd)');
endheader_len = decode_int(A(5:8));
if (header_len == 6)
elseerror('Header length != 6 bytes.');
endformat = 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');
endnum_tracks = decode_int(A(11:12));
if (format==0 && num_tracks~=1)error('File is format 0, but num_tracks != 1');
endtime_unit = decode_int(A(13:14));
if (bitand(time_unit,2^15)==0)midi.ticks_per_quarter_note = time_unit;
elseerror('Header: SMPTE time format found - not currently supported');
endif (rawbytes)midi.rawbytes_header = A(1:14);
endctr = 15;
for i=1:num_tracksif ~isequal(A(ctr:ctr+3)',[77 84 114 107])  % double('MTrk')error(['Track ' num2str(i) ' does not begin with track ID=MTrk']);endctr = 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);endctr = ctr+track_len;
endfor i=1:num_trackstrack = track_rawbytes{i};if (rawbytes); midi.track(i).rawbytes = track; endmsgCtr = 1;ctr=9;  % first 8B were MTrk and lengthwhile (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)==255type = 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); % ?elseB  = 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);endendswitch msg_typecase '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])endendctr = 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 bytetype = B;thedata = [];chan = [];endlast_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);endmidi.track(i).messages(msgCtr) = currMsg;msgCtr = msgCtr + 1;end % end loop over rawbytes
end % end loop over tracksfunction val=decode_int(A)val = 0;
for i=1:length(A)val = val + bitshift(A(length(A)-i+1), 8*(i-1));
endfunction 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;
elsedisp(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 < 2vel = 0;
end
if nargin < 3ts = 0.01;
endNnotes = size(Notes,1);n1 = round(Notes(:,5)/ts)+1;
n2 = round(Notes(:,6)/ts)+1;if vel == 0vals = ones(Nnotes,1);
elsevals = Notes(:,4); % velocity
endfor i=1:NnotesPR(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.操作步骤与仿真结论

5.参考文献

MIDI文件格式分析 - 百度文库

A03-11

6.完整源码获得方式

方式1：微信或者QQ联系博主

方式2：订阅MATLAB/FPGA教程，免费获得教程案例以及任意2份完整源码

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【MID音频读取和分析】基于matlab的MID音频文件读取和分析

1.软件版本

2.理论知识

3.核心代码

4.操作步骤与仿真结论

5.参考文献

6.完整源码获得方式

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