Just trying to wrap my head around
intervals but I'm confused by
If I am playing a chord on a piano, how do you play a
Unison chord if you can't press the same key twice at the same time? What's the purpose of
Well, first of all, a unison is an interval ; as such, it makes sense to want to designate is, as you would do with any concept.
Especially as it is used in real life. You sometime play with other people. In an orchestra, for example, chords are usually played across several parts. Several parts could very well be playing the same note in a chord, and you have to designate the interval between these notes somehow.
In a choir, sometimes every voice sings the same pitch at the same time. The choir sings in unison.
On the violin we often double-stop the same note twice, for example playing an open string A whilst simultaneously playing the same pitch on the D string (typically with a fourth or second finger.) But obviously on a piano things are different.
However there are still practical reasons to play the same note with different fingers on the piano as these answers note:
And beyond the practical, the concept of a unison chord has theoretical value even if you never play one.
You're right that you can't press one key on the piano twice at the same time. Usually in cases where a not appears twice in the same place, it's a point where the parts meet. For example there's a piece I'm playing just now where a low point in the treble and high point in the bass are the same note at the same time. It's displayed with 2 stems to make the point that it is a part of both melodies, but in practical terms it is the same note.
It's a bit odd to describe something as a unison chord, because generally a chord only takes one occurrence of a note into a consideration. So for example if violin and viola were both playing the same note of a chord, the chord name does not change.
The purpose of unison depends on the situation. For example one note can be played by multiple instruments so that the qualities of both sounds combine to make something new, or in composition terms you might be forced to use a unison because no other note in the sequence will fit.
Unison often means the same pitch notes played on different instruments, but musically it can mean the same NOTES played or sung together in different octaves : when sopranos and tenors are singing in unison they most likely will be singing an octave (maybe two ) apart. It it still called singing in unison.
Guitars may be played using notes on adjacent strings, one or two frets apart, with the lower bent up to match the higher.It's called a unison bend. Obviously, piano wise, playing in unison will sound no different from playing separate notes - two fingers on a key sounds like one. Play the same notes simultaneously with another instrument - unison !
you cannot play a unison at the piano. Also, there's no such thing as a 'unison chord', a unison means two sounds that are at the same pitch. It's obvious with two instruments, but with only one, even though you can't play unisons at the piano, if the composer still wrote it, he did it because of part-writing considerations.