This format allows for dual pokey chip songs (8-channel stereo mode). The Atari XE/LE series home computers only came with a single pokey soundchip. The feature to compose this way is available in Raster Music Tracker.

There are many players that can play back .SAP files, though some earlier players might not play back 8-channel SAP files correctly.

View sap (format) for more infos.. . .