% WAVWRITE WAVWRITE Write a WAV Audio File
% 
% Usage
% 
% The wavwrite funtion writes an audio signal to a linear PCM WAV
% file.  The simplest form for its use is
% 
%     wavwrite(y,filename)
% 
% which writes the data stored in y to a WAV file with the name
% filename.  By default, the output data is assumed to be sampled at a
% rate of 8 KHz, and is output using 16 bit integer format.  Each column
% of y is written as a separate channel.  The data are clipped to the
% range [-1,1] prior to writing them out.  If you want the data to be
% written with a different sampling frequency, you can use the following
% form of the wavwrite command:
% 
%    wavwrite(y,SampleRate,filename)
% 
% where SampleRate is in Hz.  Finally, you can specify the number of
% bits to use in the output form of the file using the form
% 
%    wavwrite(y,SampleRate,NBits,filename)
% 
% where NBits is the number of bits to use.  Legal values include
% 8,16,24,32.  For less than 32 bit output format, the data is
% truncated to the range [-1,1], and an integer output format is used
% (type 1 PCM in WAV-speak).  For 32 bit output format, the data is
% written in type 3 PCM as floating point data.
function wavwrite(varargin)
  SampleRate = 8000;
  NBits = 16;
  if (nargin == 2)
    y = varargin{1};
    filename = varargin{2};
  elseif (nargin == 3)
    y = varargin{1};
    SampleRate = varargin{2};
    filename = varargin{3};
  elseif (nargin == 4)
    y = varargin{1};
    SampleRate = varargin{2};
    NBits = varargin{3};
    filename = varargin{4};
  else
    error('unrecognized form of wavwrite call.');
  end
  if (~any(NBits == [8 16 24 32]))
    error('unsupported number of bits in output.');
  end 
  if (NBits < 32)
    y = max(-1,min(1,y));
    if (isvector(y)) 
      y = y(:); 
    end
  end
  fp = fopen(filename,'w+b','le');
  fwrite(fp,uint8('RIFF'));
  % Write a placeholder for the filesize
  fwrite(fp,uint32(0));
  fwrite(fp,uint8('WAVE'));
  fwrite(fp,uint8('fmt '));
  fwrite(fp, int32(16));
  if (NBits == 32)
    fwrite(fp, int16(3));
  else
    fwrite(fp, int16(1));
  end
  NumChannels = size(y,2);
  SampleFrames = size(y,1);
  BytesPerSample = NBits/8;
  fwrite(fp,int16(NumChannels));
  fwrite(fp,int32(SampleRate));
  fwrite(fp,int32(SampleRate*NumChannels*BytesPerSample));
  fwrite(fp,int16(NumChannels*BytesPerSample));
  fwrite(fp,int16(NBits));
  fwrite(fp,uint8('data'));
  nbytes = NumChannels*SampleFrames*BytesPerSample;
  fwrite(fp,uint32(nbytes));
  if (NBits == 8)
    fwrite(fp,uint8(y'*127+128));
  elseif (NBits == 16)
    fwrite(fp,int16(y'*2^15));
  elseif (NBits == 24)
    fwrite_24bits(fp,int32(y'*2^23));
  elseif (NBits == 32)
    fwrite(fp,float(y'));
  end;
  p = ftell(fp);
  fseek(fp,4,'bof');
  fwrite(fp,uint32(p-8));
  fclose(fp);  
  
function fwrite_24bits(fp,data)
  t = int2bin(data(:),32);
  lo = bin2int(t(:,25:32));
  med = bin2int(t(:,17:24));
  hi = bin2int(t(:,9:16));
  s = [lo,med,hi]';
  fwrite(fp,uint8(s));
  
