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Rhythmic Patterns and Rates of Activities
Durations of sounds (the length of time in which the sound exists) combine to create musical rhythm. Rhythm is based on the perception of a steadily recurring, underlying pulse. The pulse does not need to be strongly audible to be perceived. The underlying pulse (or metric grid) is easily recognized by humans as the strongest, common proportion of duration (note value) heard in the music.
The rate of the pulses of the metric grid is the tempo of a piece of music. Tempo is measured in metronomic markings (pulses per minute, abbreviated "M.M."), or in some contexts as pulses per quarter note. Tempo, in a larger sense, can be the rate of activity of any large or small aspect of the piece of music (or of some other aspect of audio, for example the "tempo of a dialogue").
Durations of sound are perceived proportionally in relation to the pulse of the metric grid. The human mind will organize durations into groups of durations, or rhythmic patterns. In the same ways that we perceive patterns of pitches, we perceive patterns of durations. Pattern perception is transferable to all of the components of all of the artistic elements, and is the traditional way in which we perceive pitch and rhythmic relationships.
Rhythmic patterns are the durations of or between occurrences of an artistic element. Rhythmic patterns might be created by the pulsing of a single percussion sound; in this way rhythmic patterns would be created by the durations between the occurrences of the starts of the same sound source. Rhythmic patterns comprised of the durations of successive, single pitches (perhaps including some silences) creates melody. Rhythmic patterns of the durations of successive chords (groups of pitches) creates harmonic rhythm. In this way, rhythm can be transferred to ALL artistic elements. For examples, it is possible to have rhythms of sound location (as is becoming a very common mixing technique for percussion sounds); it is likewise possible to have timbre melodies, or rhythms applied to patterns of identifiable timbres.
Sound Sources and Sound Quality
The selection, modification, or creation of sound sources is an important artistic element of audio recording. The sound quality of the sound sources (the timbre of the source), plays a central role in the presentation of musical ideas, and has become an increasingly significant resource for the expression of musical ideas.
The sound quality of a sound source may cause a musical part to stand out from others, or to blend into an ensemble; in and of itself, it can convey tension or repose, or lend direction to a musical idea; it can add dramatic or extra-musical meaning or significance to a musical idea; finally, the timbral quality of a sound source can, itself, be a primary musical idea, capable of conveying a meaningful musical message.
Until the Twentieth Century, composers of Western music used the sound quality of a sound source
(1) to assist in delineating and differentiating musical ideas,
(2) to enhance the expression of a musical idea by the careful selection of the appropriate musical instrument to perform a particular musical idea, or
(3) to create a composite timbre (or texture) of the ensemble, thereby forming a characteristic, overall sound quality.
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