6. Time and rhythm

Music unfolds in time. Rhythm and metre depend on duration, order, and recurrence. They give us the structures we use to predict, move, and coordinate. This chapter begins with broad ideas of time and rhythm, then turns to timing, the question of when a single sound happens. From there it turns to pulse and tempo, to entrainment as the mechanism that lets us move to a beat, and to metre as the hierarchy that entrainment builds. We then zoom in on microrhythmic nuance and end with the phenomenon of groove. This chapter runs across all the four levels of description. An onset is a physical event you can find in a waveform; a perceptual centre is where the ear puts it; a backbeat that feels laid-back rather than late is interpretation. Here, we will explore how they compare.

Time¶

Time in music refers to the organisation of sounds and silences in a temporal framework. It is the foundation on which rhythm, beat, and metre are built. Musical time is also more than clock measurement: it is shaped by perception, culture, and performance practice. Rhythms and metres may be notated in a score, but their feel depends on how musicians and listeners interpret and embody them.

Time scales¶

Sound and music span a range of time scales, and different scales are handled by different parts of the hearing system and the brain. The figure below lays them out on a logarithmic axis, where each step is ten times longer than the last. At the fast end sit differences of a few tens of microseconds between the two ears, which the auditory system uses to locate a sound source (see psychoacoustics). Waveform periods between about 0.05 and 50 ms are heard as pitch rather than as separate events. After that, we start hearing individual events, and rhythmic structures may emerge.

Figure: Time scales of sound and music (blue) and of the body and its surroundings (orange) on a logarithmic axis. The grey band marks the range in which Fraisse placed perceived rhythm. The ranges are approximate and drawn for orientation, not measured.

The psychologist Paul Fraisse distinguished between rhythms that are perceived and rhythms that are conceived Fraisse, 1982. Perceived rhythms have intervals of roughly 200–1800 ms, which is the range of subdivisions, beats, and short groupings. Faster events fuse into a single sound: you can hear this happen with the From pulse to pitch app, where a click repeated faster and faster turns from a series of pulses into a buzzing tone once the gaps are shorter than a few tens of milliseconds. Slower cycles have to be counted or remembered rather than felt. The upper limit is related to the few seconds that auditory short-term memory can hold at once, which is also about the length of a musical phrase.

The body keeps time at several of these scales too. Walking steps come about twice a second and running steps about three times a second, the heart beats about once a second at rest, and a breath takes around four seconds. Slower still are the cycles that chronobiology studies Koukkari & Sothern, 2006: hormonal rhythms of an hour or two, the 24-hour sleep–wake cycle, the menstrual cycle of about a month, close to the lunar cycle, and the annual cycle of the seasons that governs migration and hibernation. None of these are perceived as rhythms in Fraisse’s sense, but they form the background against which musical time is experienced, and they can couple to music, as the sections on entrainment below and the chapter on physiology show. At the slow end of the axis, the appliances in a room switch on and off with periods of minutes, a case we return to at the end of the chapter.

Clock time and felt time¶

A clock measures duration; a listener feels it. Psychologists separate judgements of duration, how long something lasted, from judgements of the passage of time, whether it seemed to pass quickly or slowly Wearden, 2015. The two do not always agree. A three-minute song and three minutes of silence have the same duration, but they are not felt to be the same length, and a long concert can pass in a flash while a short wait feels endless. The classic explanation is an internal clock whose ticks are counted and compared with memory, so that a faster clock, driven by arousal or attention, makes an interval feel longer Allman et al., 2014. More recent accounts suggest that the brain keeps several parallel timelines that are recalibrated as events unfold rather than one central clock.

Rhythm¶

What is rhythm? Everyone knows one when they hear it, yet the word is hard to pin down. At its most general, rhythm is about repetition. In biology it has been defined as “a change that is repeated with a similar pattern” Koukkari & Sothern, 2006, and Anne Danielsen, borrowing a phrase from the poet Amiri Baraka, describes musical rhythm as a “changing same” Danielsen, 2010. Both definitions include the heartbeat, the tides, and a fridge switching on and off, and this chapter uses rhythm in that broad sense whenever it looks beyond music.

In music the term usually means something narrower: a pattern of durations formed by the intervals between the perceived time points of notes. Notice the word perceived. A rhythm is not the sound signal itself but the pattern of time points a listener hears in it. This is why the same recording can be heard as several rhythms, and why the perceptual centre of a sound, discussed later in this chapter, matters as much as its physical onset.

Rhythm in notation¶

Western notation writes such patterns of durations with note values. Each value is half the length of the one before it, from the whole note down through half, quarter, eighth, and sixteenth notes, and every value has a rest of the same length for silence. A dot extends a value by half, and a tuplet squeezes three notes into the time of two. Note values say nothing about how long a note lasts in seconds; that is fixed only when a tempo is chosen.

Figure: Note values and rests in Western notation. Each row fills one bar of 4/4 with twice as many notes as the row above, so the halving lines up vertically, and the second bar of each row shows the rest of the same length. The last row shows a dotted quarter and a triplet.

Rhythms can be periodic (based on cycles, such as a metronome) or aperiodic (irregular, as in speech or improvisation). Both can be meaningful: a drum groove in 4/4 and a free jazz solo each have rhythm, but in different senses.

Rhythms also carry cultural meaning. A clave rhythm in Afro-Cuban music is more than a sequence of durations; it is a structural reference for musicians and dancers. In the same way, speech rhythms shape the flow of rap and spoken-word performance.

Rhythm as a signal¶

Rhythms are often drawn as points on a timeline, but both bodily and musical rhythms are carried by continuous signals that can vary in the three ways we discussed in the acoustics chapter: period (time taken by one cycle), amplitude (strength of each cycle), and its phase (the position within the cycle at a given moment). All three return later in the chapter: the period sets the tempo, differences in amplitude mark the accents of a metre, and phase is what a tapping finger aligns when it entrains to a beat.

“Perfect” rhythms are rare. A metronome comes close, but few people would call a metronome musical. What makes music interesting is that its rhythms are not perfect. Much of the research presented in this chapter, from tapping to swing, is about how much, and in what way, real rhythms depart from perfect ones.

Rhythm is also tied to movement. Eric Clarke argues that rhythm and timing can be “seen as the consequence of movement, and rhythm and timing seen as the source of, or motivation for, movement” Clarke, 1999. That two-way link between hearing a rhythm and moving to it runs through the sections on tempo, entrainment, and groove.

Timing¶

In rhythm studies, it is crucial to say when a sound happens. This is a much harder question than it sounds. A sound has a physical onset that can be found in the waveform, a moment at which the ear places it, and several landmarks in between. The distance between these is small, often a few tens of milliseconds, but it is the same size as the timing differences that give music its feel, so it has to be sorted out first.

Onset timing¶

When we speak of the “timing” of instruments in performance, we usually mean onset timing: when each sound begins. In a recording, the physical onset is the moment the waveform starts to rise out of the silence or the background. Finding it automatically is a standard task in audio analysis, and the algorithms for it are treated in machine listening. A sound has other timing landmarks too:

• Physical onset: the moment the sound begins in the waveform
• Energy peak: the moment the sound is loudest
• Attack time: the time from the physical onset to the energy peak
• Perceptual centre: the moment the ear places the sound at, which is the subject of the next section

Figure: The amplitude envelope of one tone with the timing landmarks used in rhythm research. Schematic, after Nymoen et al. (2017).

Perceptual centre and attack time¶

When listening to rhythms, the “moment of occurrence” of a sound, the point we use to place it in time, often does not coincide with its physical onset. This percept is usually called the perceptual centre (P-centre) or perceived attack time (PAT): a subjective reference point that typically falls somewhere after the physical onset and before the peak of the sound’s energy.

Studies show that certain sound parameters affect where P-centres are heard. Attack duration or time (from onset to peak) is the strongest factor: faster attacks yield earlier P-centres, and slower attacks yield later ones. Total duration (from onset to offset) has a weaker but similar influence, with shorter sounds shifting P-centres earlier and longer sounds shifting them later. A RITMO study that varied the attack, duration, and frequency of drum sounds and synthetic tones confirmed this pattern, and also found that slow-attack sounds have a wider, less precise P-centre Danielsen et al., 2019. Anne Danielsen describes the consequence as a beat bin: the beat is not a point in time but a window, and the sounds that mark it decide how wide the window is.

Figure: Two sounds starting at the same instant. The ear places the sharp, short one almost at its onset and the slow, long one well after it. Schematic; the millisecond values are illustrative.

Timbre and timing¶

The P-centre results have a practical consequence: what plays affects when it is heard. Here, the timbre of the instruments (its sound “colour”) is important. Because the P-centre depends on the attack, two musicians who want to sound together cannot simply start their notes at the same instant. A bassist with a soft, round attack has to play slightly ahead of a drummer’s sharp snare stroke for the two to be heard as synchronous, and a choir, whose consonants take time to form, will sound behind a piano unless the singers anticipate. Producers meet the same problem from the other side: lining up tracks by their waveform onsets in a digital audio workstation does not guarantee that they sound “tight”, so many align by ear instead. Timbre also decides how precisely timing can be judged at all.

Take two guitar chords, one played by slowly arpeggiating the strings (“swept”) and one played by stroking all the strings in quick succession (“swift”). Although both come from the same instrument, the swept stroke tends to sound as if it occurs slightly later relative to its physical onset, while the swift stroke has a P-centre much closer to its onset timing.

Image source: adapted from Câmara et al. (2020).

The figure below shows the consequence for a sequence. Three identical sounds with evenly spaced onsets sound evenly spaced (A). Replace the middle one with a slow-attack sound and the onsets are still even, but its P-centre falls late, so the sequence sounds uneven (B). The same holds for sounds that start together: they sound together only if their P-centres coincide, not their onsets.

Figure: Three sounds with identical onset spacing. In A they also sound evenly spaced. In B the middle sound has a slow attack, its P-centre (dashed) falls late, and the sequence sounds uneven even though the onsets are not. Schematic, after Villing (2010).

Space and timing¶

Recall from acoustics that sound travels at about 343 metres per second. Two musicians 10 metres apart therefore hear each other about 30 ms late, which is more than the asynchronies that give a groove its feel. In a symphony orchestra the distance from the double basses to the first violins can exceed 20 metres, which is one reason players follow the conductor’s visible beat rather than the sound from the far side of the stage.

The same problem appears when musicians play together over a network. In experiments where two people clapped a rhythm together through an artificial delay, tempo stayed stable up to a delay of roughly 10 to 20 ms and then slowed steadily as the delay grew, because each player waited for the other Chafe et al., 2010.

Rooms add an additional spatial effect. Reverberation prolongs every sound and smears the onsets that timing perception depends on, so fast, detailed rhythms that are crisp in a dry studio become a wash in a cathedral. Music written for reverberant spaces tends, accordingly, to move slowly.

Pulse and tempo¶

With the timing of single sounds settled, we can turn to the regular series of them that a listener feels as a beat, to how fast it goes, and to the rate at which the body would set it on its own.

Pulse¶

The beat (also called the tactus or pulse) is the basic time unit of music: the regular series of moments that a listener feels the music moving in. A pulse can also describe an ongoing stream of beats; one can speak of 8th-note pulses just as much as quarter-note pulses. Either way, the beat level is what we naturally tap our feet to, giving stability and predictability to performers and listeners alike.

Research suggests that we comfortably perceive and move to beats when the time between them (the inter-onset interval, IOI) lies between about 500 and 700 ms, that is, 86–120 BPM. Pulse is thus closely tied to our sensorimotor system: we tend to move along with it. Faster events are heard as subdivisions, and slower ones are grouped into larger spans.

Note that in music, the pulse is not always marked by sound. Even when silent, it can be inferred as a virtual reference that organises events. Musicians often “feel” the pulse even when they play around it.

You can explore this with the Silent beats app, which loops one bar of 4/4 with a pulse of four clicks and a rhythm on a grid of sixteenths. Any click or event can be silenced, the pulse can drop out for whole bars, and the rhythm can be rotated against the beat, so that the same durations fall on different levels of the metric hierarchy.

Tempo¶

Tempo is the rate of the beat, measured in beats per minute (BPM). In notation the beat is often the quarter note, but the tempo is a property of what is heard, not of how it is written.

Scores give the tempo either as a metronome marking such as ♩ = 120, exact in beats per minute, or as an Italian tempo marking such as andante, which names a character as much as a speed.

Markings also change tempo within a piece: accelerando and ritardando for a gradual speeding up or slowing down, and rubato, literally stolen time, for the performer’s freedom to stretch and compress the beat expressively. All of these describe the beat level; the subdivisions and bars scale with it.

Spontaneous motor tempo¶

Recall the exercise at the beginning of this chapter. When done in controlled studies, most people will settle at around 100–120 BPM, an interval of roughly 500–600 ms between taps. This rate is called the spontaneous motor tempo (SMT) Fraisse, 1982. It varies between people, is fairly stable within a person from day to day, and slows with age.

The spontaneous motor tempo also matches the rate of walking, and sits close to the tempo at which people most easily hear and follow a beat, which peaks at around 120 BPM Moelants, 2002. Much dance music lives in the same range, or a little faster, to “make” you move.

The overlap between tapping, walking, and preferred musical tempo is one of the clearest signs that musical time is rooted in the moving body. Tapping is also the standard laboratory task for studying timing: in sensorimotor synchronisation experiments, people tap along with a metronome and the timing of each tap is measured against the click Repp, 2005. How the body produces timing, from tapping to whole-body movement, is the subject of a section in the body.

Entrainment¶

Entrainment refers to the synchronisation of a person’s movements or internal rhythms with an external rhythm, such as a musical beat. This is the course’s main treatment of the idea, so it is worth stating in its general form before we narrow it to music.

Coupled oscillators¶

The underlying physics is that of coupled oscillators: two systems that influence each other, however weakly, tend to fall into a stable phase or frequency relationship rather than drift independently. The first recorded case had nothing to do with music: in 1665 Christiaan Huygens noticed that two pendulum clocks hanging from the same beam fell into step with each other, and found that the tiny vibrations travelling through the beam were enough to hold them there. Nothing about that is specific to music, or even to biology. What makes it useful here is that a great many things about a person oscillate, including attention, limb movement, breathing, heart rate, and populations of neurons, and a musical pulse is a periodic signal that all of them can couple to.

Entrainment therefore returns twice more in this course, each time with a different oscillator on the receiving end: as coordination between people in the body, and as measurable alignment of breathing and cardiac rhythm in physiology. The mechanism is the same one in each case.

Figure: A simulation of Huygens’s clocks. Two pendulums with periods of 1.00 and 1.04 s drift apart while isolated; their phase difference winds round and round. From 20 s they are weakly coupled through a shared support, and within a few swings they lock into anti-phase, swinging in mirror image.

Measuring entrainment¶

You can measure your own entrainment with the Tap along app, which scores the mean and spread of your tap timing against a click at any tempo. Most people find that their taps land slightly before the click, by a few tens of milliseconds, which shows that they are predicting the beat rather than reacting to it; the section on producing rhythm in the body explains why. Entrainment can also be read from the whole body. In a motion capture study of people moving to grooves whose beat markers had been shifted by a few tens of milliseconds, the listeners’ movements followed the shifts, without the listeners noticing that anything had changed Danielsen et al., 2015.

Interpersonal synchrony and joint action¶

Much of this chapter focuses on one person locking attention and movement to an external pulse. Making music together adds coordination between people: ensembles, choirs, and dance partners stabilise a shared tempo, align their movements, and predict each other’s timing. The mechanism is the entrainment described above, now with people coupling to each other as well as to the music. The empirical side of such joint action, from ensemble playing and dance to claims about social bonding, is taken up in the body.

Metre¶

Metre provides a hierarchical framework for the organisation of rhythm, such as 3/4 or 4/4 metres in music. A metric system typically includes a nested system of pulses at several periodicities, from fast subdivisions to slower bar lengths:

• Beat (pulse/tactus): the fundamental beat we tend to synchronise or entrain to (e.g. the 1–2–3–4 in a 4/4 metre)
• Division levels: subdivisions of the beat (e.g. 8th, 16th, and 32nd notes)
• Multiple levels: slower groupings of the beat (e.g. half-notes and bar-lengths)

Figure: One bar of 4/4 seen as a stack of pulse levels. Each dot is a pulse; the beat level in the middle is the one listeners usually tap to.

In notation, metre is written as a time signature at the start of the staff. The lower number gives the note value that counts as one pulse and the upper number how many of them make a bar. Beams then show the grouping: 3/4 and 6/8 both hold six eighth notes, but 3/4 beams them in three pairs and 6/8 in two threes, which is exactly the difference between three beats and two. A signature such as 7/8 has beats of unequal length, here 2+2+3, which the section on asymmetric metre below takes up.

Figure: One bar each of six time signatures on a rhythm staff, drawn to the same scale so that the bars show their relative lengths. The accents mark the beats and the beams show how the pulses are grouped into them.

Subdivision¶

Subdivisions divide each beat into smaller units. We tend to hear them as subdivisions when their IOI duration is between about 100 and 500 milliseconds. Subdivisions add detail and density, and they often act as stylistic markers (e.g., straight eighths in rock, sixteenths in funk, triplet-based 12/8 in blues).

Drum parts are written on a percussion staff, where the lines and spaces stand for instruments rather than pitches. In the common layout the bass drum sits in the bottom space, the snare in the third space, and the hi-hat (a pair of cymbals on a stand, opened and closed with a foot pedal) above the staff with an x-shaped notehead. The three patterns below differ mainly in their subdivision: eighth notes on the hi-hat in the rock beat, a long–short triplet feel in the 12/8 shuffle, and sixteenths in the funk pattern, while the kick and snare keep their places.

Figure: Three drum patterns on a percussion staff, two bars each, differing in the subdivision of the hi-hat. The bass drum sits in the bottom space, the snare in the third space, and the hi-hat above the staff with an x-shaped notehead. These are the rock, shuffle, and funk presets of the drum machine app.

The Drum machine app lets you hear this directly: one bar of four beats, each divided into two, three, or four steps, on which you draw kick, snare, and hi-hats. Each hit can be soft, medium, or strong, so the grid can also carry a metric accent, the subject of the next section, and a swing control sets the long–short ratio of each pair of subdivisions.

Metric accent¶

Western music theory traditionally frames metre as a pattern of strong and weak accented beats (e.g., ONE-two-THREE-four in 4/4), with accents thought to align where metrical levels overlap. In practice, this is not always how music is felt or performed. Many groove-based styles emphasise off-beat positions. The downbeat is beat 1 of the bar, an upbeat is the beat or part of a beat that leads into it, and the offbeats are the positions between the beats, such as the “and” in “1-and-2-and”. In popular genres such as rock, soul, and R&B, the snare backbeats on 2 and 4 can feel more salient than beat 1. In reggae, the offbeats on the “ands” may dominate more than the downbeats. Metrical accents, then, are not fixed; practice and cultural convention can redefine them.

Metre as entrainment¶

Metre can be thought of as entrainment applied to listening. Once a listener has locked on to a beat, attention rises and falls with it, peaking where the next beat is due and dipping in between. It does so at several levels at once, for the subdivision, the beat, and the bar. In this view metre is not a grid printed on the page but a pattern of expectation in the listener, and a metrical accent is simply an event that arrives when attention is at a peak. This is the dynamic attending theory, and the figure below shows the idea.

Figure: Two levels of periodic attention and their sum. An event landing inside a tall peak is heard as metrically accented; one landing on a slope is heard as early or late. Schematic, after Large & Palmer (2002).

Think of metrical accent strength as the height and narrowness of an attention peak. Stronger regularity and clearer cueing tighten the window for “on-time”, while looser surfaces widen it without losing the beat. At RITMO, we have done EEG studies that show how the brain prepares its response before an expected beat arrives, both for strictly periodic rhythms and for irregular patterns that are learnable Solli et al., 2025.

Asymmetric metre¶

Not all metres divide evenly into twos (binary) and threes (tertiary). Asymmetric metres (such as 5/8 or 7/8) have beats of different durations, organised into uneven groupings of equal subdivisions, like 3+2 or 2+2+3. They are common in Balkan, Middle Eastern, and contemporary art-music traditions.

Performers often feel such metres as cycles of unequal steps rather than a uniform grid. The asymmetry can produce a sense of lilt or forward drive distinct from even metres.

The Metre explorer app lets you hear and see this. A cycle of pulses is grouped into beats, from 2/4 to 11/8 and any grouping you type in, drawn as a circle and as a line whose beat lengths show their durations.

Asymmetric metres are one corner of a much larger world of rhythmic patterns that do not fit a grid of equal beats and binary subdivisions. In Norwegian telespringar, for instance, the three beats of the bar are long, medium, and short, a case the chapter returns to at the end.

Microrhythm¶

Microrhythm refers to the fine-scale timing and shaping of events around our subjective reference structures (beat, subdivision). Unlike beat- and subdivision-level rhythms, microrhythm concerns variations in timing at a scale below 100 ms. The ethnomusicologist Charles Keil called such small timing and tuning discrepancies between players participatory discrepancies, arguing that they are what give music its characteristic feel.

At RITMO, many researchers have worked on understanding more about how microrhythm influences music perception and cognition. This has been spearheaded by Anne Danielsen’s work on funk and groove, beginning with her analyses of James Brown and Parliament Danielsen, 2006 and continuing with more fundamental research on microrhythm Danielsen et al., 2024.

Asynchrony and non-isochrony¶

In terms of timing, we can speak of two related but different forms of microrhythm: asynchrony and non-isochrony. Asynchrony refers to the way musicians can play in a more synchronised (“on-beat”) or asynchronous way (early/“pushed” or late/“laid-back”) relative to one another. Non-isochrony relates to how they might skew the durational ratio of metrical subdivision levels (e.g., 8th or 16th notes) to varying degrees, from isochronous (“straight”) to non-isochronous (“swung”).

Microrhythm can encompass both expressive moment-to-moment nuance and systematic patterns that recur across a piece or style. In many performance traditions, those systematic patterns are the norm, rather than “deviations” from an ideal of perfect metronomic or isochronous timing.

Figure: The reference grid (dashed) has a mean subdivision interval m. Asynchrony displaces events by d in one direction; swing displaces only the even-numbered subdivisions, producing alternating long and short durations. Redrawn after Câmara et al. (2025), Figure 1.

Beat delay and anticipation¶

Musicians sometimes play behind or ahead of the beat in a systematic way, whether consciously or not. In rock and soul styles, snare strokes on beats 2 and 4 of a 4/4 metre are often said to be delayed, and in funk, downbeats are said to regularly anticipate “One”. What counts as “late” or “early” always depends on a reference in the given context, whether kick, snare, or the overall grid.

Different degrees of beat delay/anticipation are said to convey different feels. Delayed (late) backbeats in groove styles are often described as “laid-back”: a relaxed feel when only slightly delayed, but a “heavy” or “dragging” feel if delayed too much. Anticipated (early) beats are described as “on-top/pushed”, which at lower magnitudes can sound “snappy” and “driving”, but too much may sound “nervous” or “rushing”.

Figure: A producer’s rule of thumb for how far ahead of or behind the beat to place events, and what each amount feels like. Redrawn after Stewart, in Prögler (1995).

Swing¶

Subdivision notes need not be isochronous (equal), as they are in a straight-8ths hi-hat pattern in rock. Swing, a form of non-isochrony (non-equal durations), describes systematic long–short patterns at the subdivision level.

In jazz, musicians typically do not swing at a perfectly mechanical “triplet swing” ratio of 2:1. Instead, swing ratios in performance can range from close to 1:1 (straight) all the way up to 3:1 (dotted swing) and beyond, depending on tempo, sub-genre, personal style, and other factors. In funk and hip-hop, by contrast, sixteenth notes tend to be swung more subtly (e.g., 1.2:1) unless played in explicit funk-shuffle styles (closer to 2:1, triplet). Swing also depends on tempo. In a study of a samba groove performed at several tempos, the uneven sixteenth notes became more even as the tempo increased, so the same groove has a different swing ratio when played slow and fast Haugen & Danielsen, 2020.

Different swing ratios are thought to impart different degrees of “motional energy” to rhythms. Rhythms with lower swing ratios (closer to 1:1) are described as more “continuous”, “driving”, or “propulsive”, whereas higher swing ratios (up to 2:1 and beyond) tend to give “bounce” or “choppiness”, often accentuating the downbeats and on-beats of the metre.

Perceptual thresholds of microrhythm¶

Recall from psychoacoustics that the just-noticeable difference (JND) is the smallest change a listener can reliably detect. Microrhythm has its own JNDs, and they are surprisingly small: differences of a few tens of milliseconds are enough to change how a groove feels. How small depends on the sounds involved (sharp drum attacks are easier to judge than blended sustained tones), on tempo and note density, and on musical training.

Groove¶

Groove can be understood in many ways: as a rhythmic pattern, as a way of playing, and as the pleasurable urge to move that such playing produces. The word has travelled from an LP record’s physical groove to jazz slang and has later also become a research concept Câmara & Danielsen, 2019. Here we focus on groove as “pattern” and as “performance approach”, with an eye on time and rhythm.

As a pattern, a groove can be defined simply as a persistently repeated rhythm, often spanning one or two bars, whose events establish a clear beat and a characteristic subdivision layer. The beat may be externalised (e.g., a kick/snare backbeat in 4/4) or implied by cyclic “isoperiodic” figures that recur predictably. Style identity often hinges on the basic unit (the smallest repeating chunk) and its density referent (the shortest subdivision practically used).

As performance, a groove is the coordinated realisation of that basic unit across parts (e.g., drums, bass, guitar/keys, vocals). Players distribute roles: some layers reinforce the beat (e.g., kicks on beats 1 and 3, snare on 2 and 4), while others supply tension by playing on off-beat subdivisions (e.g., bass accentuating the “2-and”). Grooves often balance stability (an easily entrainable pulse) with off-beat devices that add interest and complexity, such as syncopation and cross-/counter-rhythm (see below).

Syncopation¶

Syncopation is often described as a local contradiction of a metrical expectation: a note on a weak-position accent, a tie across a strong beat, or the omission of a strong beat followed by sound on a weak one. In 4/4, common cases include stressing the “and” of 2 or 4, tying into 1, or placing a salient event on 3-and while 3 itself is silent. Because the beat is usually firmly established in groove styles, such contradictions tend to add tension without destabilising the metre.

Listening experiments confirm the link to groove: adding syncopation to plain synthesised patterns increases how much listeners want to move, up to a point beyond which the pattern becomes too irregular to follow Sioros et al., 2014.

Counter-/cross-rhythm¶

When syncopated events recur systematically within the basic unit, they can form larger-scale, patterned off-beat groupings that suggest alternative periodicities to the main beat.

Cross-rhythm (often called “polyrhythm”) occurs when these groupings display a systematic overlap of rhythmic streams whose periodicities (i.e., “metrical levels”) are non-integer multiples. Typical examples in 4/4 are two evenly spaced events over three beats (2:3 cross-rhythms) or four events over three or six beats (4:3 or 4:6 cross-rhythms). The regular pattern of overlapping accents contradicts the beats of the prevailing metre, challenging it and creating greater metrical ambiguity, to the point where one might hear the pulse as either binary or triplet.

Figure: Cross-rhythms as two simultaneous pulse streams. The two streams meet only at the start of each cycle (vertical lines), which is why they blur the sense of a single pulse.

In most groove styles, though, such overlapping rhythms are usually bounded. They tend to span less than a bar and to coincide again with beat-confirming positions of the metre before repeating. This generates less metrical ambiguity without fundamentally challenging the main pulse. Typical counter-rhythmic groupings in 4/4 are 3+3+2 over eight eighth notes, or 3+3+3+3+2+2 over sixteen sixteenths; listeners may hear secondary “pulses” riding on top of the main metre. The 3+3+2 grouping is the tresillo introduced in the note on rhythmic patterns earlier in this chapter.

Figure: Four counter-rhythmic patterns written in 4/4. The tresillo and the 3+3+3+3+2+2 grouping are the two mentioned above; the cinquillo and the two-bar son clave are their Afro-Cuban relatives from the note on rhythmic patterns.

A room’s tempo¶

Everything in this chapter so far has run on musical time scales: onsets tens of milliseconds apart, beats around half a second, phrases lasting a few seconds. However, periodicity can be found everywhere in the world.

Think about the rhythmic nature of many machines. Motors, refrigerators, and ventilation systems all run with different types of duty cycles. A refrigerator typically turns on and off a couple of times per hour. A dishwasher adds a single long phrase with its own internal wash, rinse, and dry structure on top of that pulse.

A critical look: when beats refuse to be equal¶

Most rhythm research, and most music software, quietly assumes that the beats of a metre are isochronous. For rock, pop, and EDM the assumption mostly holds. Not so much for folk and experimental music.

• The claim under test is that metre rests on equal beats, so that any unevenness is expressive deviation from an underlying regular grid.
• The evidence says otherwise for Norwegian folk music. Measurements of telespringar performances show bars divided into stable long–medium–short beats, in proportions that remain consistent across tunes and performers Haugen, 2016.
• The method combined audio analysis with motion capture of a fiddler and a dancing couple. The fiddler’s foot stamping and the dancers’ vertical motion followed the same non-isochronous pattern, suggesting a shared bodily reference structure rather than sloppy timing.
• The limits are a small number of performers, one regional style, and proportions that vary somewhat between players and districts. The finding does not overturn metre theory; it shows that the reference grid itself can be uneven and learned.