The most common and most likely answer to this crossword clue is the 7 letter word PICCOLO
I've seen this crossword clue in Independent
P
I
C
C
O
L
O
More clues leading to the result PICCOLO
- Choose a deep sound? Not from this!
- Photo leading to surprised comment about large instrument
- Image surprisingly cool for an orchestral instrument
- Picture army officer with old musical instrument
- Choose a deep-sounding instrument
- Instrument panel initially at 100, taking in 200 AND 50 later
- Instrument for body running tests in VW
- Flute of champagne first served in cool half-pint, perhaps
- Instrument viewed in kaleidoscopic colours
- Source of music in film company parking area mostly
Buddy explains!

The straight part
We know that "Instrument" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case instrument = piccolo.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 PICCOLO mean?
PICCOLO noun- An instrument similar to a flute, but smaller, and playing an octave higher.
- A waiter's assistant in a hotel or restaurant.
- A bottle of champagne containing 0.1875 liters of fluid, 1/4 the volume of a standard bottle; a quarter bottle or snipe.