A phrase can seem to change its stride even when the smaller pulses keep moving at the same speed. One way to create that effect is hemiola. In a familiar example, six equal pulses are heard first as two groups of three, then as three groups of two.
The Aaron Shearer Foundation’s rhythm lesson demonstrates this change of grouping in 6/8. The LilyPond music glossary places hemiola in the broader context of a three-to-two relationship. The exercise below explores one accessible version, rather than every historical or compositional use of the term.
Keep the small pulses, move the emphasis
Count six evenly spaced pulses repeatedly. First emphasise pulses one and four: ONE, two, three, FOUR, five, six. Then emphasise one, three and five: ONE, two, THREE, four, FIVE, six.
Keep the gap between every pulse unchanged. The second pattern has three main accents where the first had two, but the full cycle still takes the same time. If you speed up to fit the extra accent, restart more slowly. The useful discovery is the change in grouping, not an increase in pace.
Listen for the context around the pattern
A row of six notes by itself does not establish how a passage is being felt. Listen to the accompaniment, the phrase before it and where the strong events fall. A temporary regrouping becomes more apparent when a surrounding pattern gives the listener an expectation.
Try tapping the smaller pulses while another person speaks the two accent patterns in turn. Swap roles. Then listen without tapping and notice whether you can still hear the underlying spacing.
Describe what changed before naming it
In a concert note, write the observation first: “the accents shifted from two groups to three across the same span.” If a score or reliable analysis is available, use it to check your interpretation. A sudden rhythmic surprise might involve another device instead.
Learning the term gives that particular surprise a useful name. Keeping the pulses steady gives your ears a way to understand why it happens.