The Beat Is Something You Supply

Set a metronome going: identical clicks, evenly spaced, no accents. Listen for thirty seconds.

You will start hearing them in pairs. One-two, one-two, with the first of each pair stronger. The metronome is not doing that. You are.

Psychologists call it subjective rhythmisation, and it has been documented since the nineteenth century. Given a neutral sequence, listeners impose grouping and accent, and different listeners impose different ones. The beat is a collaboration between the sound and the person hearing it, and a good deal of music exists to exploit the gap.

Once a pulse is established it is remarkably robust. It survives silence (a band can stop dead for two bars and come back together, with the audience still counting) and it survives passages where nothing marks it at all. Entrainment of this kind is one of the few musical capacities that looks close to universal, and it is what makes dancing possible.

It also means two people can lock onto the same music in different places and each be certain the other is wrong. This happens constantly with music that begins on an upbeat or has an ambiguous texture, and since the metre is supplied rather than contained, there is frequently no fact of the matter until the music does something to disambiguate.

The famous case is the clapping. An audience clapping on beats one and three where the band is playing two and four is not simply unhip; they have adopted a different metrical interpretation of the same sound. Harry Connick Jr's celebrated response, adding a beat so the audience's claps landed on two and four, is a demonstration that the disagreement is about position, not tempo.

Which brings us to the backbeat, the organising fact of nearly all popular music since the 1950s.

In most European art music the metrical weight falls on the first beat of the bar. In music descending from African American practice, the snare drum hits hard on two and four, against that expectation, and the whole feel of the music depends on the tension between the two. Rock, soul, funk, reggae and hip-hop are all built on it. Remove it and the music does not merely sound different; it stops working.

Syncopation is the general case, and it has a precondition that is easy to miss: it only exists relative to a metre the listener is holding.

An accent off the beat is off something. If the grid has not been established, the displaced accent just becomes the beat and the effect evaporates, which is why very dense syncopation stops sounding syncopated and starts sounding merely irregular. The device is parasitic on the expectation it violates, and a good arranger keeps enough of the metre audible for the violation to register.

Then there is music that maintains two metres at once.

West African and Afro-Cuban traditions use patterns that can be heard as three groups of two or two groups of three, and players move between the readings deliberately. The ambiguity is the material, not a difficulty in it. European music calls this hemiola and treats it as a special effect, usually near a cadence; in the traditions where it is ordinary grammar, a listener is expected to hold both readings and feel them rub.

Describing this as rhythmically complex says something about the training of the listener rather than about the music. A listener taught to maintain exactly one metre at a time finds it hard. A listener raised on it finds the European habit of keeping the metre unambiguous at all times strangely thin.

The practical upshot, for anyone listening rather than playing: when a piece of music confuses you rhythmically, the useful question is not what the time signature is. It is where you are putting the pulse, and what happens if you put it somewhere else.