Level 6-1 is the song composed by Vance Kozik for Super Noah's Ark 3D that is played in Level 6-1. The song is the same for both the DOS and SNES releases, but the different audio hardware plays them each with a distinct sound.
Super Noah's Ark 3D (SNES)
Level 6-1 tune is heard in Level 6-1 and is along the rarest because this is only used in one level (the other one is Level 5-5).
The song is output to S-SMP chip.
Super Noah's Ark 3D (DOS)
Level 6-1 song on the DOS game is not only played on E6M1 but also on the high scores screen (note: the Nintendo version did not have any of such screen, though the scores system itself presented, making the music track rare)
The type-0 DOS MIDI file's meta data refers to the track as "NOAH11.imf", even though it is not an IMF file. This is to make it compatible with Wolfenstein 3D music engine. The song itself is output to OPL2.