Rhythm

One of the properties of sound that changes in music is loudness – volume increases and decreases over time. Usually, these volume changes are repetitive, occurring with a steady pulse. This pulse is rhythm, the fundamental characteristic of music.

Rhythm echoes natural phenomena. The beating heart drives a pulse that is rhythmical. Footsteps of a walking person and the hoof beats of a running horse produce a rhythm. Rhythm in music mimics these natural pulses. It does this with alternating periods of sound and silence. The simplest rhythm is composed of a sound of unvarying loudness and duration alternating with periods of silence of uniform duration. A common example of this sort of pulse is the dripping of a leaky water faucet.

Each sound is the same as the other sounds, and the silences are also all alike.

To investigate how rhythm works we will be using mainly recordings of synthesized sounds, in order to reduce any outside associations with the sound. The first sample contains a fading burst of white noise lasting 0.1 second that is followed by 0.4 seconds of silence. This is repeated 40 times for a total duration of 20 seconds.

If you are like most people, while listening to this you may have begun to hear not a sequence of identical bursts, but alternating beats, differing in loudness or timbre, first a louder (or brighter) beat, then a quieter (or duller) beat. The louder, brighter one seems to be more prominent or accented. Listen again to see if this didn’t indeed happen. It is quite normal for a steady uniform pulse to be perceived as a pulse composed of alternating accented and unaccented beats. Our brains make this adjustment automatically, perhaps because we are bipedal, and the fundamental rhythm of our walking motion is the ONE-two pulse of footsteps. Our two legs are not identical, one is always perhaps a little stronger or a little longer, and the difference between them produces the ONE-two rhythm of walking at a steady pace.

When we hear a steady series of uniform beats, it is our tendency to hear them as a ONE-two pulse. However, because the actual sounds are the same, our perception can shift and the accent can transfer spontaneously from one beat to the next—the pulse is indefinite and ambiguous. In music, this ambiguity is usually removed by using beats that are not uniform but that actually differ in loudness or timbre. The basic beat in music is a ONE-two pulse, where the beats alternate in some fashion: in loudness, in timbre, in duration, or in some combination of these. The next example contains a rhythm produced by alternating loud and quiet beats. The louder, accented beats are 0.1-second pulses of noise, and the unaccented beats are not as loud and slightly different in timbre.

Because we humans find the ONE-two pulse so easy to hear, it forms the basis of much music, especially music designed for walking or marching. Here’s a bit of a march from John Philip Sousa; hear the ONE-two.

Additional rhythms can be created by following the louder beat with two softer ones, producing a 3-beat rhythm.

This rhythm, ONE-two-three, is epitomized in European music in the Waltz, a folk dance that originated in Bavaria around 1750 and spread throughout Europe. Here’s a bit of waltz from the Russian Peter Tchaikovsky. Hear the ONE-two-three.

The elaboration of rhythmic patterns can continue by adding three soft beats after a louder one, or even four soft beats after the louder one.

What you may notice when listening to the ONE-2-3-4 pattern for a while is that the “3” seems to become a bit more prominent. This is another result of our natural inclination to hear a ONE-two pulse – the ONE-2-3-4 beat slips into ONE-two-THREE-four. Because the ONE-2-3-4-5 beat cannot divide easily into ONE-two, what you may hear happening is that the fourth beat seems to become stronger. You may hear a ONE-2-3-FOUR-5, or ONE-two-three-ONE-two, pattern. A 5-beat pattern breaks apart into alternating 3-beat and 2-beat patterns. So, in most music, the fundamental rhythms are based on the ONE-two pulse and the ONE-two-three pulse.

The ONE-two pulse and the ONE-two-three pulse are the basic building-blocks of rhythm in music, but in making music, much is done with them. They are varied in many ways, from very simple to extremely complex. Perhaps the simplest variation on a pulse is to vary its speed, or as it’s called in music, its tempo (which is Italian for time). The pulse can be slowed by lengthening the silences between beats. In the following example, the silences have been lengthened from the 0.4 second of the earlier sample to 0.9 second.

The sound bursts now occur once per second, rather than twice per second, producing a pulse that is half the speed. This slower pulse feels more relaxed, perhaps calmer.

Alternatively, the pulse can also be sped up by shortening the silences between beats. In the next example, the silences are now only 0.15 second and the overall pulse is twice as fast as that in the original. This faster pulse feels more excited, perhaps nervous.

In the faster pulse, you may have noticed something else, as well. Your tendency to hear a ONE-two beat may have given the impression that the original ONE-two is still there at the same speed, but that there are additional beats between the original ones. This gives an impression of a pulse that composed of four beats: ONE-and-TWO-and. (Listen again to see if you can hear this.) It seems as though the original pulse has been subdivided by the insertion of additional beats. There is ambiguity in this faster pulse; is it a fast ONE-two or is it a subdivided slower ONE-two? This ambiguity is just one of many features of perceived rhythm that music makers use to deepen the interest of their music.

The tendency to hear a ONE-two pulse shows up, too, when a ONE-two-three pulse is sped up. In the next sample, the speed of the ONE-two-three pulse has been doubled by shortening the silences from 0.4 second to 0.15 second.

You can hear the rapid ONE-two-three-ONE-two-three pulse, but you can just as easily hear a pulse like ONE-tick-tick-TWO-tick-tick, where the TWO beat sounds a bit different from the ONE pulse although it is actually the same. This is the same altered perception that allowed you to hear a ONE-two pattern in the repetition of identical beats in the one-beat earlier. Here though, we pick out a slower ONE-two from the louder beats and discount the intervening softer beats that make up the faster rhythm. Not only do we have a proclivity to hear a ONE-two pulse, but we tend to hear it at a speed corresponding to a comfortable walk.

In a uniform stream of beats we are often able discern more than one pulse. This ability is exploited in much music when more than one pulse are purposely used simultaneously. In the simplest cases, the accents in each pulse occur simultaneously. As an example, we will combine a ONE-two pulse with a ONE-two-three pulse. To make the two pulses easier to distinguish, each will use a beat at a distinct frequency. The ONE-two pulse uses a 200-Hz beat.

The ONE-two-three pulse uses a 400-Hz beat.

When heard simultaneously, you can easily switch between hearing the ONE-two pulse and hearing the ONE-two-three pulse.

A rhythmic pattern gains interest when it contains more than one pulse. The following example demonstrates this:

As each pulse is added, the rhythm becomes more animated, more exciting, more involving. Our bodies tend to move along with the rhythm. The slower pulse tends to animate the largest parts of our bodies, and we move our head, our hips and shoulders, swaying with the rhythm. The faster pulse gets our legs and feet in motion. The fastest pulse animates our arms and hands. Then, as the faster pulses are removed, the rhythm relaxes, and our bodies become calmer.

This superposition of two simultaneous beats has been used to stirring effect in many musical compositions. In this example, the opening to George Friedrich Händel’s coronation anthem, Zadok the Priest, a ONE-two pulse and a ONE-two-three-four pulse are played simultaneously, suggesting both something important (ONE-two) yet stirring (ONE-two-three-four) is about to happen. When the chorus begins to sing, their beat is even slower than the ONE-two of the opening, indicating that something monumental is happening, specifically the coronation of a new monarch.

Much music employs a rhythm that is fairly constant, that is, the music has a regular pulse. This music fits the description “easy to dance to.” We can move our bodies smoothly and consistently with music that has a regular pulse. Yet, variations in rhythm can add interest to music. One variation in rhythm that is frequently used is a shifting of the accented beat. For example, the pulse may change from ONE-two-ONE-two-ONE-two to ONE-two-ONE-two-one-TWO. Such a shift in accent can give an unexpected jolt to the rhythm. The next example contains a steady pulse in which the accent shifts several times from one beat to another.

Any variation in the rhythm that changes the regular pattern of strong and weak beats is called syncopation. Shifting of the accent from one beat to another is a form of syncopation. An example of how this sounds in a piece of music is the beginning of the opera “Akhenaten” by Philip Glass.

This shifting is often done in vocal music by placing the words not on the accented beat but on one of the minor beats. Such shifting can add tremendous interest to the words, making for a much more “catchy” song. A notable example of this shifting occurs in “Satisfaction” by the Rolling Stones, where the words “I can’t get no” are off the main beat.

Another type of syncopation involves the occasional skipping of a beat that would normally occur, or leaving unaccented what would normally be the accented beat. The pulse continues as though the skipped beats were not missing. The example contains a pulse in which several beats are missing.

The pulse seems to stop, then continue as normal, creating a halting effect to the pulse. Missing beats is a common feature of reggae music, and it can be heard in Delroy Washington’s “Freedom Fighters,” where the main beat is often left unaccented.

Another rhythmic variation or syncopation that can add a certain fascination to music involves a modification to the pulse itself. The basic pulse remains constant, but an occasional beat is placed slightly ahead or behind where it would be expected.

These off-pulse beats give a jerkiness to the pulse, making it less predictable, and simultaneously, more stimulating. It is almost impossible to resist moving your body when the off-pulse beat occurs, which is why this type of syncopation is popular in dance music. This technique was exploited to great effect by George Gershwin in his “Fascinating Rhythm.”

Syncopation often involves two identical pulses that are somewhat out of synchronization. In order for the syncopation to be heard clearly, the pulses must differ in something other than the rate of the pulse, such as pitch or timbre. The following two examples contain ONE-two-three pulses that beat at the same rate. The first, however, contains beats at a frequency of 400 Hz and the other at a frequency of 800 Hz.

Next, these two are combined in syncopated fashion. The 400 Hz beats start and set the basic rhythm, then the 800-Hz beats are added so the accented beats occur slightly after the accented beats at 400 Hz. Both ONE-two-three pulses can be heard at the same time.

This type of syncopation is sometimes used in music that has two (or more) melodies occurring at the same time. The pulse of one melody is slightly offset from the pulse of the other, which makes it easier to hear both tunes at once. In the opera Lucia di Lammermoor by Gaetano Donizetti, two characters simultaneously sing two different melodies with their pulses slightly offset, which makes them easily distinguishable.

A more elaborate form of this two-pulse syncopation involves not two identical pulses, but two that are different. The simplest form of this is the combination of a ONE-two pulse with a ONE-two-three pulse, in which both the ONE-two and the ONE-two-three units take the same amount of time. In the example, the ONE-two pulse has two 400-Hz beats per second, and the ONE-two-three pulse has three 800-Hz beats per second.

The effect of combining these produces a more complex but stable rhythmic pattern in which the two-beat and three-beat patterns can still be discerned. In the next example, a 3-beat-per-second pulse is combined with a 2-beat-per-second pulse.

Such a two-over-three beat pattern is used in the popular “Carol of the Bells.”

A three-beat pattern,

and a four-beat pattern of the same duration,

can be combined to form a four-over-three beat pattern.

Such a pattern occurs in the song “Till the World Ends” as performed by Britney Spears.

Although rhythm is an essential component of music, the musical examples presented here show that music is more than just a pattern of beats in time. Music has other equally important features as well, especially melody, which is the subject of the next section.