INSIDE THE MUSIC

Key: A Harmonic language: Mainly blues-based I7 IV7 V7 Tempo: ≈81bpm (perceived as 162bpm) Novel features: A significant number of irregular bars in blues-rock context

Adeeply important mechanism in musical expression is rhythmic prediction. When we hear a sequence of sounds, our brains automatically start looking for patterns. We (usually completely unconsciously) rapidly make ‘best guesses’ about how events might proceed, and adapt these ‘predictive maps’ accordingly. A simple example is if we hear two identical pulses a second apart, then we will expect a third a second later. (Figure 1.)

Figure 1: a model of rhythmic prediction.

If it comes, then it confirms (and strengthens) our assumptions. If it doesn’t, we experience some dissonance, surprise, delight or confusion, and then we adapt our models based on this new information and come up with a ‘better explanation’ for what we’ve heard. In this case perhaps that the rhythm is based on a ‘one-second grid’, but some of the pulses are ‘missing’ – essentially a framework with gaps, as illustrated in Figure 2.

Figure 2: an illustration of a predictive grid, where a series of sounding events are perceived in terms of their placement (or gaps within) a regular grid.

To complicate matters, these predictions are happening on multiple ‘time levels’. We predict in terms of the next beat, grouping of beats, bar or higher sectional levels, and these predictions are variously met or thwarted. Which explains how nuanced, complex and varied our responses to musical rhythm are. Figure 3 illustrates this ‘multi-level’ predictive map. The lowest layers may be beats or subdivisions of the beat, leading up to the bar and higher-level groupings of bars.

Figure 3: an illustration of a multi-layered predictive grid.

That brings us to Black Dog. The guitar textures, blues harmonies, vocal tone and drum patterns of this track set us up to expect familiar predictable ‘binary’ beat patterns, four beats in a bar in four bar sections, and the first four bars meet this expectation. The vocal rhythm includes four similar phrases, each starting rhythmically identically, which strongly set up a 4/4 expectation.

However, after the vocal introduction, where we expect a strong fifth bar we get… nothing. This is followed by Page’s three-note guitar upbeat line and then the band entering confidently on (what would have been) beat three. However, it shortly becomes clear that the band are entering on a strong downbeat, and our predictive map has to be reset to accommodate this new information. The following figure illustrates this remapping.

Figure 4: an illustration of the predictive resetting in Black Dog.

Another notable section occurs from 0:37, where Page and Jones’s three-note motif shifts in placement against Bonham’s steady 4/4 pulse. These sorts of rhythmic disruptions have many terms in musicology (‘partial-bar links’, ‘polymeter’, ‘phasing’ etc), but essentially they create internal dissonances which are processed as surprising, jarring or delicious, depending on your tastes. Black Dog is riddled with such irregularities. They never challenge prediction on the ‘beat level’ – the beats are all similar lengths and appear as predicted – however barlines are often shifted from their expected placement, creating a sense of deception and rhythmic ‘rug-pulling’. These devices transform what would be a fairly straight-ahead blues-rock tune into an edgy and progressive track, on the boundary of familiarity and disarming.