The durations of tonal music are divisible by the pulse. Pulses are organized into measures. Measures are organized by patterns of accents. Accents result from both rhythmic placement and harmonic content. The stability of consonance implies strong metrical placement. The embellishing character of dissonance implies relatively weak metrical placement. Techniques of syncopation, however, may displace a strong beat to a weak one by reversing these implicit associations. The affect of tonal music arises in large part from this interplay of pitch and rhythm. Consonance and dissonance, metrical uniformity and irregularity, all conspire to create dramatic patterns of expectations met, frustrated, and finally resolved. Read on........
Rhythmic OrganizationInformally, we call the temporal aspect of music its rhythm. How tonal music unfolds in time, however, is quite complex, and the relative duration of successive events, their rhythm, is only one part of temporal organization. There are four, altogether: pulse, tempo, rhythm, and meter.
PatterningOur sensory nervous systems navigate safely through this complex and threatening world by distinguishing pattern (important stuff -- originally survival related ), from noise (unimportant stuff). One of the ways in which our auditory nervous systems detect patterns is to keep a temporary list of the most recently heard sounds in "short-term-memory" and compare sets of incoming sounds to them.
We recognize the incoming sound-stream as a reiteration or variant of the pattern in memory if their essential features are similar, especially features related to their beginnings. This is done at the unconscious neurological level, without engaging the higher cognitive functions of the brain. After all, at one time our ancestors had to recognize important life-threatening sounds and respond with "reflex-speed".
The Pulse
One of the simplest and most basic types of auditory patterns is the pulse-train. . .a series of sounds (not necessarily the same sound), the beginnings of each being equally separated in time. We often refer to the sensation of a pulse-train as feeling the beat.
We call to the number of pulses per minute the Tempo . The tempi for the examples were 72, 300, and 10 respectively. The tendency to group pulses, or supply intermediary pulses is not fully understood; but it is probably an attempt by the brain to impose upon what is heard a temporal structure more in keeping with other bodily rhythms (for example heart-rate, breathing, walking, and chewing).
Whenever we do this, and for whatever reason, we are producing meter. . .the organization of pulses into groups focusing on or emphasizing certain pulses over others. Music that incorporates meter is called metric music.
In many musical cultures (especially in the 20th century popular music of the West), entire musical layers (the rhythm-track), instruments (the drums), and even sections within ensembles (the rhythm section), are given the task of "keeping the beat", making the pulse-train and the meter audible.
In Western European art-music, however, the metric structure of the music only becomes audible by the careful composition and coordination of four types of accent:
harmonic accents created by patterns of pitch=intervals
agogic accents created by the relative durations and duration patterns of the pitches,
tonic accents created by the contours and repetitions produced by organized strings of pitches, and
dynamic accents created by the relative loudness or volume differences between pitches.
Rhythm and Meter
A succession of durations is a rhythm. There are three basic types of musical rhythm: free, multimetric, and isometric.
A free rhythm is one in which we perceive only the relative length of successive notes.
A multimetric rhythm is one in which every duration is a whole-number multiple of some smaller unit of duration.
An isometric rhythm is a multimetric rhythm in which the resulting durations group themselves into larger units of equal duration called measures.
As a rule, the rhythms of functional tonality are isometric. Isometric rhythm has three components: rhythm, pulse, and meter.
The interplay of harmony and melody organizes pulses into groups. We call the arrangement of pulses into groups meter. We call the pulse groupings themselves measures or bars. The division between measures is shown with a vertical line through the staff called the bar line. We specify the meter of a musical work with a meter signature or time signature.
The meter signature appears after the key signature at the beginning of a musical work. A meter signature has two parts.
The Numerator. The top number gives the number of pulses in a measure.
The Denominator. The bottom number gives the note value that corresponds to the pulse.
For example, 34 indicates a meter in which there are three pulses to the measure, with each pulse having the value of a quarter note. The meter signature 48 indicates a meter in which there are four beats to the measure, with the eighth note acting as pulse. Like other meters of the type, 34 and 48 are called simple meters. For simple meters, these simple relations hold. But there is another type of meter called compound. For compound meters, the meter signature provides more ambiguous information.
Tonal music presents us with two types of meter: simple meter, and compound meter. The pulse of each differs.
A simple meter has a simple pulse. A simple pulse divides into pairs of smaller note values. The numerator of a simple meter signature gives the number of pulses in a measure. The denominator gives the note value that corresponds to the pulse. As a rule, the numerator of a simple meter will be less than six.
Musicians sometimes refer to 44 as common time. The symbol c often replaces the meter signature and stands for common time or 44. Similarly, musicians often call 22 cut time (or, more formally, alla breve). The symbol  replaces the meter signature and stands for cut time or 22 .Compound meters have compound pulses. A compound pulse divides into three parts. Since all our note values divide naturally in half, we must represent a compound pulse with a dotted note value. It is impossible to represent a dotted note value with a simple integer, though. As a result, the denominator of a compound meter does not show the note value of the pulse. Rather it shows the note value of the largest equal subdivision of the pulse.
To interpret a compound meter signature then, we must first divide the numerator by three. This gives us the number of pulses in the compound measure. Then, we must group together three of the note values given by the denominator. The combined duration of these three values gives the duration of the pulse.
For example, 68 is a compound meter. The 8 represents the largest equal subdivision of the pulse. Three of these subdivisions make up the pulse, so three eighth notes equal one pulse. Our pulse, then, is three eighth notes long, or the duration of a dotted quarter note. There are six eighth notes in the measure, so there are two pulses to the measure. (A pulse equals three eighth notes. A measure equals six eighth notes. Six divided by three equals two pulses.)
As a rule, the numerator of a compound meter will be greater than five, and it will be divisible by three.
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