wavemap: Avoid resampling if possible

[Francois Gouget]

The distorsion that lead to my previous patch was in fact caused by the 
resampling of an 11025Hz signal to 48kHz. According to the signal 
processing literature I could find, what we do is a '1st Order Linear 
Interpolation Filter' and that is considered a poor filter. That 
literature says we should be using an 'nth Order Interpolation / 
Decimation' filter.

I didn't really feel motivated enough to implement such a beast, plus 
this is more the job of a sound library than of Wine. I hope aRts, 
ESound, Jack and friends implement such a filter so it will hopefully 
soon be a moot point soon anyway. However one easy thing we can do is to 
try not to do any resampling unless absolutely necessary. This means 
first trying simple 8/16bits or mono/stereo conversions first. If we 
find a match the sound quality will be better and the conversion will 
use less CPU.


Changelog:

    Francois Gouget <fgouget at codeweavers.com>

  * dlls/winmm/wavemap/wavemap.c

    Our resampling algorithm is quite primitive so try simple 8/16 
mono/stereo conversions first. Only resample if we cannot avoid it.


-- 
Francois Gouget
fgouget at codeweavers.com

-------------- next part --------------
Index: dlls/winmm/wavemap/wavemap.c
===================================================================
RCS file: /home/wine/wine/dlls/winmm/wavemap/wavemap.c,v
retrieving revision 1.26
diff -u -r1.26 wavemap.c
--- dlls/winmm/wavemap/wavemap.c	13 Dec 2002 02:18:20 -0000	1.26
+++ dlls/winmm/wavemap/wavemap.c	13 Dec 2002 19:18:56 -0000
@@ -185,6 +191,19 @@
 #define	TRY(sps,bps)    wfx.nSamplesPerSec = (sps); wfx.wBitsPerSample = (bps); \
                         if (wodOpenHelper(wom, i, lpDesc, &wfx, dwFlags | WAVE_FORMAT_DIRECT) == MMSYSERR_NOERROR) \
                         {wom->avgSpeedInner = wfx.nAvgBytesPerSec; goto found;}
+
+        /* Our resampling algorithm is quite primitive so first try
+         * to just change the bit depth and number of channels
+         */
+        for (i = ndlo; i < ndhi; i++) {
+            wfx.nSamplesPerSec=lpDesc->lpFormat->nSamplesPerSec;
+            wfx.nChannels = lpDesc->lpFormat->nChannels;
+            TRY(wfx.nSamplesPerSec, 16);
+            TRY(wfx.nSamplesPerSec, 8);
+            wfx.nChannels ^= 3;
+            TRY(wfx.nSamplesPerSec, 16);
+            TRY(wfx.nSamplesPerSec, 8);
+        }
 
         for (i = ndlo; i < ndhi; i++) {
             /* first try with same stereo/mono option as source */