octave

An octave spans eight scale degrees and represents the most fundamental interval in music. Two notes an octave apart share the same letter name and sound like the same pitch at different heights. This is because the upper note vibrates at exactly twice the frequency of the lower — the simplest possible frequency ratio after the unison. The octave is the basis of the musical pitch system. The standard piano has just over seven octaves, from A0 to C8. Playing in octaves — both hands or both notes struck simultaneously — is a common technique for adding power and brilliance. Liszt and Rachmaninoff wrote famously demanding octave passages that require both strength and flexibility.