The "patch" is supposed to change sound and music playback from the default 22 kHz / mono format to 44 kHz / stereo format. This provides primarily a higher quality music playback in the game, and additionally, the few stereo sound effects will now also play in stereo instead of mono. (If I remember correctly, the only stereo sound effects in the game are the "new day" and "new week" sounds, and those short pieces that play at the beginning of battles.)
Although it hasn't been tested with all version of the game, it'll probably work with any versions, with or without any expansions, and should be compatible with any mods and operating systems. It should also work with Heroes Chronicles.
This patch has also been incorporated into the HD mod (at least from what I can tell by their changelog), starting from version 2.80. Therefore, if you have a recent version of that mod installed, you probably don't need to install this fix separately from here.
Link to the newest version of the fix (19 September, 2010):
If you have an older version of the fix already installed, you should uninstall it first.
To install this fix, simply copy the fixed mss32.dll file found in the archive to the game's installation directory, overwriting the existing file there. Do make a backup of the game's original file first, in case you need to restore it (if the patch doesn't work, for example).
The rest of this post details the older versions of this fix. You don't need to read it, unless the above fix doesn't work for you and you want to try one of these older releases instead.
- Exe patcher from 9 January, 2010:
This is basically the same thing as the newest release, but it patches the game's exe files instead of mss32.dll, so I consider it less practical. Further information is available in the readme file within the archive.
- DirectShow-based mss32.dll fix from 10 June, 2008:
1. Go to your Heroes 3 installation directory.
2. Rename the file "mss32.dll" to "mss32old.dll". (Make sure you rename it correctly - the patch will need this file to work.)
3. Copy (extract) the "mss32.dll" file from the zip into the Heroes 3 directory.
If you want to uninstall the fix, just delete 'mss32.dll' and rename the backup 'mss32old.dll' to 'mss32.dll'.
This version is not compatible with Windows Vista/7.
How this version works: The patch replaces the MP3 playback functions of the original mss32.dll with new ones, and forwards everything else to the original dll (including sound effect playback, so those few stereo sound effects will still play in mono). The new functions are implemented via DirectShow. The DirectShow filters that the fix uses should be available by default on Windows XP, and possibly on older Windows systems as well. If it's not the case, the game will probably crash or just won't play any music - let me know if this happens. The filters are not available on Windows Vista/7, therefore the game will crash in the main menu if you attempt to run it with this fix under either of those operating systems.