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Bug 477

Summary: mono->stereo and other upsampling conversions produce poor sound
Product: SDL Reporter: Jacob Meuser <jakemsr>
Component: audioAssignee: Ryan C. Gordon <icculus>
Status: RESOLVED FIXED QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2 CC: alfredo, brad
Version: 1.2.13   
Hardware: All   
OS: All   
Attachments: updated patch against 1.2.13

Description Jacob Meuser 2007-08-11 20:14:54 UTC 
when SDL converts audio, it often degrades the overall sound quality.  This is noticeable even when doing just mono->stereo, and just 22050 Hz -> 44100 Hz.  these are the simplest upsampling conversions.

bug #298 hits on this and suggests that the fix isn't complete.  I believe the correct fix is below.  desired->size is of no consequence, audio->spec.size is the real buffer size.

this patch is against 1.2.9

--- src/audio/SDL_audio.c.orig	Fri Sep 17 06:20:10 2004
+++ src/audio/SDL_audio.c	Fri Aug 10 02:19:27 2007
@@ -481,7 +481,8 @@ int SDL_OpenAudio(SDL_AudioSpec *desired, SDL_AudioSpe
 			return(-1);
 		}
 		if ( audio->convert.needed ) {
-			audio->convert.len = desired->size;
+			audio->convert.len = (int) ( ((double) audio->spec.size) /
+                                          audio->convert.len_ratio );
 			audio->convert.buf =(Uint8 *)SDL_AllocAudioMem(
 			   audio->convert.len*audio->convert.len_mult);
 			if ( audio->convert.buf == NULL ) {
Comment 1 Sam Lantinga 2007-12-29 11:56:07 UTC 
This change appears to already be in SDL 1.2.12.
Comment 2 Jacob Meuser 2008-01-03 00:50:42 UTC 
no.  1.2.12 is using desired->size, this patch uses audio->spec.size.
Comment 3 Jacob Meuser 2008-04-16 03:02:50 UTC 
Created attachment 251 [details]
updated patch against 1.2.13
Comment 4 Brad Smith 2009-01-19 03:54:32 UTC 
Could a developer please take a look at the updated patch for 1.2.13?
Comment 5 Ryan C. Gordon 2009-09-20 23:19:34 UTC 

Fixed in svn revision #4763 (and will be included in the 1.2.14 release).

--ryan.