double-system sound recording

29 LETTERS · STARTS WITH D

double-system sound recording is a valid 29-letter word worth 39 points in Scrabble and 47 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS

D2O1U1B3L1E1-0S1Y4S1T1E1M3S1O1U1N1D2R1E1C3O1R1D2I1N1G2

2 + 1 + 1 + 3 + 1 + 1 + 0 + 1 + 4 + 1 + 1 + 1 + 3 + 0 + 1 + 1 + 1 + 1 + 2 + 0 + 1 + 1 + 3 + 1 + 1 + 2 + 1 + 1 + 2 =39 PTS

DOUBLE WORD → 78TRIPLE WORD → 117

MEANING

What does double-system sound recording mean?