Harmonic Series: The harmonic series refers to a sequence of pitches that are produced by vibrating strings or air columns at different lengths. Each subsequent pitch in the series is an octave higher than the previous one.
Octave Doubling: Octave doubling is a technique commonly used in orchestration where a musical line or melody is played in unison by instruments from different families, such as violins and cellos, to create a richer sound.
Octave Equivalence: Octave equivalence is the concept that pitches separated by an octave share similar tonal qualities and are perceived as being closely related. This allows for transposition and recognition of patterns across different octaves.