【MID音頻讀取和分析】基于matlab的MID音頻檔案讀取和分析

目錄

​​1.軟體版本​​

​​2.理論知識​​

​​3.核心代碼​​

​​4.操作步驟與仿真結論​​

​​5.參考文獻​​

​​6.完整源碼獲得方式​​

1.軟體版本

matlab2013b

2.理論知識

這個部分，不涉及什麼原理，主要是對MIDI音頻信号需要了解其主要的檔案結構特點，MIDI檔案的主要結構如下：

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

3.核心代碼

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.操作步驟與仿真結論

5.參考文獻