Import of http://bugs.musicbrainz.org/ticket/2372

Some releases have a SPARS code printed on the cover. 'The SPARS Code is a three-letter code that appears on some Compact Discs recordings telling the consumer what type of tape recorder was used in the recording process, either analogue (A) or digital (D)'. I've seen it mainly being used on classical releases but it also appears on 'normal' releases every now and again.

On a release level, a dropdown can be added with four values: 'AAD', 'ADD', 'DDD' and 'DAD'. While the latter is questionable, it does appear that it has been used so we might as well include it just in case.

For more information: http://en.wikipedia.org/wiki/SPARS_Code