Cool Edit / Audition Multi Track Session file
The file itself does not contain audio data but rather settings of a multi track session such as number of tracks, wave position, amplification, equalizing, effects, etc.
Cool Edit was bought by Adobe in 2003 and renamed to Audition used the .SES binary format until CS5.5, then switch to the .SESX format.
.SES files begin with the ascii
COOLNESS for the first 8 bytes