There are many versions of Sonic CD, heres a guide through them so people don't get confused with the many ISOs floating around the Internet.
This is an obvious press release of Sonic CD, sort of a teaser. Usually called as "Sonic CD 510". Very incomplete.
Another prototype, this one is almost complete. Usually called "Sonic CD 712".
Japanese final, version 8/06
The first, Japanese release of the final game. If you set your emulator for 'Auto-Detect' the country, and this screen displays, you most likely have the JP final.
White BG morphing to black, while the SE-GA sound plays (sound effect, not voice)
Europian final, version 8/27
The Europian release of Sonic CD is the same as the Japanese one, expect for one minor thing: The game is set to 50Hz mode, and the movies were a bit edited so they won't screw up because of the speed change.
US prerelease version of Sonic CD. It's the FULL US version, before they decided to change the soundtrack. It has every change from the US version listed below, expect for the audio track change. Many people call this version as "Sonic CD 910" because the date in the ISO is 9/10. But the time stamp of the files inside it is 9/20, so the CulT calls it 9/20.
US final, version 10/16 or 10/06
US final version of Sonic CD. This one has several changes in the game:
- The title screen says TM&Ã‚Â© 1993 SEGA, on the EU and JPN ones it says Ã‚Â© 1993 SEGA
- During the game, you can "kill yourself" if you pause the game, and press one of the A, B or C buttons.
- At the race with Metal Sonic, the game will play the default music, according to the level you are in. In the JPN/EU versions, it always plays the "Bad Future" theme.
- The "Little Planet" theme is played in the Time Attack screen instead of 2nd Title screen track.
- The Audio tracks on the disc are completely changed!
SOA probably thought that the original music wouldn't apply to the american audience, so they changed the techno/pop feel music to a Rock/metal type of music, composed by Spencer Nilsen, and song by Pastiche. Download the theme of the US version here and the Original version here.
Also: the date in the ISO says 10/06, but the time stamp of the files are 10/16. Looks like SOA were lost in time when making the discs, both for the 9/20 proto and the US final.
The PC version of Sonic CD used the US soundtrack, but the PCM sounds (the "Past" music) were recorded into CD tracks. This was done because emulating the Mega CD PCM chip would require lots of CPU power (remember, this version came out in 95'). The Movies were also changed into AVIs, and the Save Game screen was also redesigned (for the better).
OEM version, using DINO libraries,
Retail version, using DirectX.
There are two known versions:
You can read the Jim Trethewey Interview for more information, he was one of the workers who ported Sonic CD to PC.