2. Sub-Saharan Africa: Bell Patterns and Polymetric Layering

If there is a single tradition that Poly’s lanes learn from, it is the ensemble drumming of West Africa (Kubik 1999 traces rhythmic practice across this region and into the diaspora that Chapter 4 picks up). In the Ewe communities of southern Ghana, ensemble music is organised around one repeating cycle: a bell pattern sets the period, and every other part — each with its own density, timbre, and social function — is placed against it. The practice has been documented in the ethnomusicological literature since the mid-twentieth century — A. M. Jones’s two-volume Studies in African Music is built largely on Ewe material⁶ — and Locke’s analysis of Southern Ewe dance drumming sets out the offbeat-timing and cross-rhythm principles this chapter builds on (Locke 1982).

This chapter is about West Africa: the Ewe of southern Ghana and, further west, the Manding. The strict polyrhythm of Central Africa — the Aka, Banda and Zande formulae Simha Arom transcribed — follows different rules, and has its own chapter: Chapter 2b.

The Gankogui Bell: E(7,12)

Every Ewe drum ensemble begins with the gankogui, the double iron bell. The bell player establishes a fixed timeline pattern that does not vary. Other drummers orient their parts relative to it, entering at different points, filling different rhythmic spaces. The bell does not lead in a melodic sense — it defines the temporal grid against which everything else is measured.

The standard gankogui pattern distributes seven strokes across twelve pulses. It is Euclidean rhythm E(7,12), which Toussaint describes as the most commonly used timeline pattern in sub-Saharan Africa — a descriptive claim about how often it appears, not a ranking of importance.¹

E(7,12)

Notice the asymmetry. The seven hits do not divide twelve evenly — they create an uneven grouping of long and short intervals (2-1-2-2-1-2-2). Locke describes the bell’s long strokes as falling in groups of two and three, separated by single short strokes, and the pattern as felt against four beats of three pulses each (Locke 1982, pp. 224–225). Seven strokes cannot sit evenly on four beats, so the bell keeps landing between them as well as on them.

You will meet this bell at more than one starting point, and it is the same rhythm each time. The diagram above starts it at rotation 0 (2-1-2-2-1-2-2); the Euclidean Reference shows it at rotation 2 (2-2-1-2-2-1-2); the bell lane of the Sub-Saharan: Agbekor preset starts it at rotation 9 (2-2-1-2-2-2-1). Rotating a cycle changes where you begin counting, not the rhythm. Locke notes that the bell’s continuous repetition makes the designation of a beginning point “somewhat inappropriate”, and that players launch it in various ways (Locke 1982, p. 225).

Role Separation: Timeline, Support, Lead

West African ensembles organise their parts into functional layers. Understanding these roles is the key to building convincing polymetric patches in Poly.

The timeline (bell) is fixed and metronomic. It never changes. In Poly, this is your anchor lane — high velocity, no mutation, no phrase gating. To lock a specific bell pattern into place so the engine cannot modulate it, use timeline mode; see Chapter 18 (Editors) for how to enter timeline mode and draw the pattern step by step.

The support drums play shorter, sparser patterns that interlock with the bell. In Ewe drumming, the kidi and sogo fill the spaces the bell leaves open. These parts respond to the timeline but remain relatively stable. In Poly, these lanes use fewer hits and lower velocity, with modest mutation values if you want subtle variation.

The lead drum (atsimevu in Ewe tradition) improvises. It plays across and against the other parts, creating rhythmic tension and release. In Poly, you model this with higher mutation percentages, phrase gating, and probability — the lead lane should breathe and vary while the timeline holds steady beneath it.

Polymetric Stacking

In an Ewe ensemble the bell sets the period, and the other parts fit inside it (Locke 1982, p. 217). In Atsiagbeko, the piece Locke draws most of his examples from, the rattle and two of the drums share the bell’s phrase length and begin with it, the high-pitched kagan drum cycles 4 times per bell pattern, and the kidi twice per bell pattern (p. 219). The cross-rhythm comes from inside that one period: the two common ratios are 3:2 and 3:4, with 3:8 sometimes (p. 244), and a cross-rhythm’s own period can be shorter than the bell’s, so several fit within one cycle (p. 233). Every part’s cycle divides the bell’s.

Poly’s extension goes further, and it is Poly’s rather than the tradition’s. Its lanes need not divide the bell at all: a 12-step bell layered with a 7-step lane does not repeat for 84 pulses, and a 5-step third lane extends the full cycle to 420 pulses — over thirty bars at 1/8 subdivision. The patch below is Ewe-inspired in that sense: an Ewe bell and Ewe roles, layered at cycle lengths Locke does not describe. The groove is always familiar but never quite the same.

E(5,12)

E(5,12) distributes five hits across twelve steps — a sparser, more open pattern that leaves room for the bell’s density.

E(3,12)

E(3,12) is the sparsest of the three, striking only on pulses 1, 5, and 9. It gives a slow, even pulse beneath the busier patterns above.

Ewe Polymetric EnsembleEwe Polymetric Ensemble

Lane	Role	Steps	Hits	Rotation	Subdivision	Timeline	Note	Velocity	Ghost	Kotekan
1	Bell timeline	12	7	0	1/8	on	56	110	30	off
2	Support drum	12	3	0	1/8	off	43	90	40	off
3	Responding drum	5	3	0	1/8	off	45	85	50	off
4	Lead complement	7	5	2	1/8	off	47	75	60	L1

To lay the dance beat under it, add a fifth lane: a low drum, 12 steps, 4 hits, rotation 0, 1/8.

Ewe Polymetric EnsembleEwe-inspired polymetric ensemble — gankogui bell timeline with kidi, sogo, and lead drum

PlayTry it

Lane 4 uses the Kotekan setting L1, which generates a complementary pattern interlocking with Lane 1’s bell. This mirrors the way a support drummer listens to the bell and fills its gaps. Set mutation to 15-25% on Lane 4 to give it the slight variability of a responding part.

What to Listen For

The 5-step and 7-step lanes create shifting accents against the steady 12-step bell. Pay attention to the moments of convergence — when all three cycle lengths align on the same pulse. Those rare unison points are an effect of Poly’s layering, not an accent the tradition places, and the tension between them is what drives this patch forward.

Manding Traditions: Djembe Ensembles

West of the Ewe heartland, the Manding traditions of Mali, Guinea, and Senegal build their ensembles around the djembe. Manding patterns, as this chapter presents them, lock to a shared cycle length but vary in density and timbre. The dunun bass drums provide a sparse timeline, the sangban plays a mid-density response, and the djembe soloist improvises over both.

A simplification

Presenting Manding ensembles as sharing one cycle length is a pedagogical simplification, not a description of the whole tradition. Charry’s survey of Maninka and Mandinka practice (Charry 2000) treats jembe drumming as one of four distinct spheres, and is where to go for what the tradition actually contains. Manding dunun ensembles do in many contexts play parts of distinct cycle lengths, and the relationship between dunun, sangban and kenkeni varies by repertoire and region. The shared cycle is used here because it is the shortest route to a playable patch that sounds idiomatic; Charry (2000), Mande Music, is where to go for what it leaves out.

You can model this in Poly by keeping all lanes at the same step count but varying hits and velocity. The effect is closer to hocketing — rhythmic interlocking within a single metric frame.

Manding Djembe Ensemble

Lane	Role	Steps	Hits	Rotation	Subdivision	Note	Velocity	Ghost
1	Dunun bass	8	3	0	1/8	36	100	0
2	Sangban mid	8	5	1	1/8	43	85	45
3	Djembe lead	8	7	0	1/8	50	95	55

Manding DjembeManding djembe ensemble — three lanes sharing an 8-step cycle with varying density

PlayTry it

Building Improvisatory Feel

Traditional lead drumming is never fully random — it follows shared vocabulary and responds to dancers and other musicians. In Poly, you approximate this not by cranking mutation to 100%, but by combining moderate mutation (15-30%) with phrase gating. Set a phrase length of 4-8 beats with a gap of 2-4 beats on the lead lane, and the pattern will breathe — playing for a phrase, resting, then re-entering with variation. The timeline and support lanes, ungated, continue without interruption.

This call-and-response structure is fundamental to West African music. The bell calls. The support responds. The lead converses with both. In Poly, you build that conversation from Euclidean lanes, and when you give them independent cycle lengths — Poly’s extension, not the tradition’s practice — no two bars are quite the same.