The most common and most likely answer to this crossword clue is the 13 letter word POTENTIOMETER
I've seen this crossword clue in The Guardian
P
O
T
E
N
T
I
O
M
E
T
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R
Buddy explains!
The straight part
We know that "Sound control" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sound control = potentiometer.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does POTENTIOMETER mean?
POTENTIOMETER noun- A user-adjustable 3 terminal variable resistor that can be used as a voltage divider.
- An instrument that measures a voltage by opposing it with a precise fraction of a known voltage, and without drawing current from the unknown source.