Torch if you were to take two trumpets that were programed exactly alike and play them together, they would sound like one trumpet. Detune each trumpet slightly and when they are played it will sound like four trumpets.
Theory:
If a C note is – let’s say a number of 100, the C note one octave above would be 200 – the next 400, and the next 800. If I were to tune the piano in this manner, no stretching, it would be a very uninteresting piano. When I stretch the tuning like the trumpets above the piano becomes alive.
If stretching is overdone, the piano will sound like a bar room piano.
Ex. C 100-- one octave above C 200.9 -- one octave above C 441.6
As a classical player plays either end of the piano he wants them dead on, no stretching. They want the piano to sound pure with no tuned effects. A jazz player wants the high end a bit higher and the lower end a bit lower. This helps him express himself.
The stretch tuning accents the 3rds, 6ths, and the 9ths. Play (on a piano) a C chord. C-E-G. When you play just the 1st and 5th C and G – not interesting. When you add the 3rd the chord begins to sing.
Piano tuners do their best at guessing how much to stretch to apply. I bought a tuning box that cost me $1,600; it measures the stretch needed; giving me the same tuning set up that the factory.
John C.
PS, Organs and keyboard have no stretching unless programmed ala Uncle Dave.