From bug-request at octave dot org Mon Dec 12 09:47:55 2005
Subject: Update: wavread(), wavwrite() (diff files)
From: Michael Zeising <michael at michaels-website dot de>
To: bug at octave dot org
Date: Mon, 12 Dec 2005 07:31:13 -0600

There's an update for the RIFF/WAVE import/export functions wavread() 
and wavwrite():

wavread 1.4, wavwrite 1.3:
o   fixed wrong scaling for 8-bit linear pcm samples
o   improved scaling for all other linear pcm resolutions
o   further minimum adaptions to octave coding style


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--- wavread-1.3.m	2005-12-12 14:07:20.000000000 +0100
+++ wavread.m	2005-12-12 14:16:49.000000000 +0100
 at @ -36,6 +36,7 @@
 ##  at deftypefnx {Function File} {[@var{samples}, @var{channels}]} = wavread (@var{filename}, "size")
 ## Return the number of samples ( at var{n}) and channels (@var{ch})
 ## instead of the audio data.
+##
 ##  at end deftypefn
 ##
 ##  at seealso{wavwrite}
 at @ -47,24 +48,20 @@
 
   FORMAT_PCM        = 0x0001;   # PCM (8/16/32 bit)
   FORMAT_IEEE_FLOAT = 0x0003;   # IEEE float (32/64 bit)
-  FORMAT_ALAW       = 0x0006;   # 8-bit ITU-T G.711 A-law   (not yet supported)
-  FORMAT_MULAW      = 0x0007;   # 8-bit ITU-T G.711 �Â��-law   (not yet supported)
-  FORMAT_IMA_ADPCM  = 0x0011;   # IMA/ADPCM 4:1 compression (not yet supported)
   BYTEORDER         = "ieee-le";
 
   if (nargin < 1 || nargin > 2)
     usage ("wavread (filename, param)");
   endif
 
-  # open file for binary reading
-
   if (! ischar (filename))
     error ("wavwrite: expecting filename to be a character string");
   endif
 
+  ## open file for binary reading
   [fid, msg] = fopen (filename, "rb");
   if (fid < 0)
-    error ("wavread: %s", msg)
+    error ("wavread: %s", msg);
   endif
   
   ## check for RIFF/WAVE header
 at @ -130,7 +127,7 @@
   if (format_tag == FORMAT_PCM)
     switch bits_per_sample
       case 8
-        format = "int8";
+        format = "uint8";
       case 16 
         format = "int16";
       case 32 
 at @ -175,27 +172,23 @@
     endif
   endif
   
-  ## read samples
+  ## read samples and close file
   [yi, n] = fread (fid, length, format, 0, BYTEORDER);
-  
   fclose (fid);
   
   if (format_tag == FORMAT_PCM)
     ## normalize samples
     switch (bits_per_sample)
       case 8
-        yi = (yi - 127)/127;      # 8-bit samples are unsigned
-      case {16, 32}
-        yi = yi/((2 ** bits_per_sample) / 2 - 1);
+        yi = (yi - 127.5)/127.5;
+      case 16
+        yi = yi/32768;
+      case 32
+        yi = yi/2147483648;
     endswitch
   endif
   
   ## deinterleave
-  ## y = [];
-  ## for i = 1:channels
-  ##   y = [y, yi(i:channels:n)];
-  ## endfor
-
   nr = numel (yi) / channels;
   y = reshape (yi, channels, nr)';
   

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--- wavwrite-1.2.m	2005-12-12 14:08:14.000000000 +0100
+++ wavwrite.m	2005-12-11 22:06:54.000000000 +0100
 at @ -58,7 +58,7 @@
   ## determine sample format
   switch (bits_per_sample)
     case 8  
-      format = "int8";
+      format = "uint8";
     case 16 
       format = "int16";
     case 32 
 at @ -121,22 +121,19 @@
     error ("wavread: writing to file failed");
   endif
   
+  ## interleave samples
+  yi = reshape (y', n*channels, 1);
+  
   ## scale samples
   switch (bits_per_sample)
     case 8
-      y = floor (y*127 + 127);
-    case {16, 32}
-      y = floor (y*((2 ** bits_per_sample) / 2 - 1));
+      yi = round (yi*127.5 + 127.5);
+    case 16
+      yi = floor (yi*32767.5);
+    case 32
+      yi = floor (yi*2147483647.5);
   endswitch
   
-  ## interleave samples
-  ## l = n*channels;
-  ## for i = 1:channels
-  ##  yi(i:channels:l) = y(:,i);
-  ## endfor
-
-  yi = reshape (y', n*channels, 1);
-  
   ## write to file
   c = fwrite (fid, yi, format, 0, BYTEORDER);
   

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