Is it always the same instrument that plays a note to tune the orchestra at the start of the concert?
While the short answer is yes, the longer answer is mostly yes, but sometimes no. First, what is the instrument you hear tuning the orchestra before a concert? It's the oboe! The oboe is a woodwind instrument with a double reed that looks somewhat like a clarinet. The oboe is a great instrument to give a tuning note for a few reasons:
It has a distinct piercing sound that's easy to hear amongst the other instruments.
Oboe players change the shape and pressure of their lips to change the pitch of the instrument, so it's easy for an oboist to adjust their pitch quickly when playing. Many other instruments have to physically move parts of their instrument to change the pitch.
The oboist isn't just playing a note out of thin air. When they give the tuning note (an A), they're usually looking at a tuner, roughly the size and shape of a cassette tape, which is a machine that picks up their sound and tells them if they're playing in tune or not.
Now, when is it not really the oboe that tunes the orchestra? If there is a piano performing with the orchestra, especially if the ensemble is about to perform a piano concerto, the pianist will play the A on the piano, the oboe then begins to play in tune with the piano, and then the rest of the orchestra jumps in to tune their instruments.
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