An arpeggio is a chord (a harmony) that is broken up into individual notes, that is, the notes are heard one at a time in succession, not simultaneously. (Read Harmony for a tutorial on what harmony is and how chords are formed). Arpeggios can occur anywhere: very frequently in the melody, and somewhat less often in the accompaniment.
Musically, the character is consonant, because arpeggios use only chord tones and therefore do not clash with the underlying harmony. Frequently the musical quality is and the melody’s , its pitch range, is wide. But not necessarily so.
Arpeggiated and scalar melodies have distinctly different sound qualities. Composers blend the two together to create melodies of vastly different and varying character.
Section B in Di Sarli’s Bahia Blanca begins with an unaccompanied bandoneon melody playing an arpeggio. It is a short example, just the first four notes; but notice the character difference between it and the descending scalar melody in the second bar:
Bahia Blanca, Section B, first 4 Bar Phrase, bars 17-20.
Another, very much longer and more robust example, is Edgardo Donato’s 1938 recording of El Adiós.
The melody is the second line. The top line is a violin counter melody, and it is not played as written. The melody is a continuous arpeggio over a regularly changing harmonic progression, ascending and descending almost entirely using only chord tones. The non-chord tones occur towards the ends of the 4 bar phrases. They are mostly scalar and the change from long arpeggiated to brief scalar melody contributes very much to the cadence effect at those points in time (bars 4 and 8).
Music that is smooth and connected, with a flowing character, often with a broad sweeping melody and gentle accompaniment.
Tessitura is a term used to describe two things, both concerning pitches in a melody or portion of music. One aspect specifically describes the pitch range, for example from the lowest to highest note in a melody. The other aspect is the music's overall pitch level, its register, such as mostly low sounding notes or mostly high sounding notes.
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