How many letters does the top answer for “magnetic tape for use in recording sound” have?

The most common answer is audiotape (9 letters).

Crossword clue: magnetic tape for use in recording sound

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

audiotape 9 letters wn-def

magnetic tape for use in recording sound

a digital tape recording of sound 50% similar → dat

a recording made on magnetic tape 50% similar → taping