Tactus and Pulse

What Is Pulse?

The perception of pulse is derived from the rhythm in music. Rhythm is the pattern of time intervals between events (usually sounds) in a sequence. For example, if one were asked to clap out the rhythm to “The Wheels on the Bus Go Round and Round,” one clap would occur for each word, and the timing of the claps would be the rhythm. The perception of rhythm is mainly determined by the times between onsets of notes. This enables a rhythm to be recognized as the same whether played with legato notes (long and connected) or staccato notes (short and separate). Rhythms typically contain a variety of different time intervals. The pulse, however, typically consists of a single time interval, regularly occurring during the rhythm. If one were asked to clap the pulse of the “Wheels on the Bus,” a clap would fall on certain words: “The wheels on the bus go round and round.”

When asked to indicate the pulse by tapping, listeners typicallytypically tap between 300 milliseconds (ms) and 1 second (although it is possible for the range of the pulse to extend from 200 ms to about 2 seconds). Adults generally show a preference for an interpulse duration of roughly 600 ms, whereas children tend to tap faster. As the tactus occurs at rates that are commonly observed in human movement (e.g., walking or chewing), it has been proposed that human perception of pulse is related to the timing regularities observed in natural movement.

Whereas rhythm is a physical property determined by the sounds in the music, the pulse may or may not be clearly audible in the music. In some musical genres, the pulse is clearly marked in the [Page 1098]music, such as when a bass drum is sounded on every beat. However, sometimes the pulse is only implied by the musical rhythm: It is “heard” in the mind of the listener, but without a clear physical manifestation in the music. Once a listener has sensed the pulse, he or she is even able to interpolate beats that are missing from the music (sometimes termed “loud rests”); the listener senses pulse when the music is actually silent. One example of this is found in the “stop time” rhythms common in blues, jazz, and tap dancing.

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