What is the term for when one instrument (let's say trumpet 1) plays a high note, while another (trumpet 2) plays a note an octave or 5 semitones lower? I want to be specific and get this correct. Thank you!
Two instruments playing an octave apart is called “octave unison” whether it’s a note or a series on notes. If they are playing lines 5 semitones apart they are playing in parallel 4ths. If it’s just one note then it’s just “in 4ths”.
Doubling an octave or a perfect 4th below.
Unison is the most used term. To some it means playing at exactly the same pitch, but technically it's the same notes, which could be in different octaves, Octave unison makes this clearer, but isn't strictly necessary.
Playing notes other than same name notes doesn't have an official name - in fact you could use 'parallel' 4ths/5ths - but that's a term used for something which in music theory isn't really 'allowed' in the 'rules'.
Prime, or perfect prime are also terms, but rarely used.
Parallel 4ths and 5ths are a term in voice leading, better called consecutive fifths, meaning notes played by the same two voices that move at the same time making the same interval of a 5th or 4th. They are allowed, just not encouraged in some styles of music Nov 16, 2022 at 7:31