Mbira songs are cyclical. The cyclical pattern for the most common type of mbira song is 48 pulses or beats in length.
The basic 48-pulse patterns are often described as being made up of four phrases of equal length. This can be a useful mechanism for analyzing the rhythmic and melodic patterns of an mbira piece.
Here's the same cycle with pauses between the phrases:
The trouble with this method is that it assumes a starting place for each phrase, when in reality mbira pieces are truly cyclical — they go round and round without any fixed starting (or ending) point.
There are (at least) two common places for starting Nhemamusasa.
To describe this you could say that in the second way of playing you are starting on the last note of the first way's phrase. Here's four phrases but starting one note earlier:
Even where there is agreement on where to start the phrases in the 48-pulse circle, there is variation in terms of which phrase one starts on. Often someone's "first phrase" is someone else's "fourth phrase"
Two common places to start Kariga Mombe are:
Whether Shona mbira players think (or have traditionally thought) of the pieces they play as being in four phrases seems to be an open question. Some have said that they do not and emphasize that the cycle can begin on any of the 48 pulses of a song. Others are said to use the four phrases as a teaching mechanism, including John Kunaka, who is quoted in The Soul of Mbira as referring to a piece's four sections. Those who teach pieces in four phrases often emphasize starting the piece at different phrases, rather than thinking of any phrase as "the first phrase." But this does not address the fact that a piece can be started at any place within these phrases.
The 12 beats of each phrase can be divided into three groups of four, or four groups of three. In this way mbira music is especially noteworthy, as it merges 4/4 and 3/4 time. Often, the music is not clearly one time signature or the other, but rather a wonderfully ambiguous combination of the two. As 12 can be evenly divided by either three or four, one can group the 12 beats into "four measures of three beats each" or "three measures of four beats each". Mbira music takes advantage of this by creating polyrhythms, in which the duple and triple meters can be heard at the same time.
Within the 48-pulse patterns, Shona mbira songs elaborate a seemingly endless number of intertwined melodic variations around a basic harmonic shape, shifting rhythms and melodies at ever-changing places in the cycle. These cyclical patterns provide a framework for elaboration and variation.
As an mbira musician plays the cyclical patterns, complex polyrhythmic and melodic patterns emerge. These interlocking patterns are inherent – and it takes some deep listening (or, ideally, playing) to begin to hear the the complexity of the relationship among the interwoven melodic lines and their resultant lines.
Heard as well are the inherent rhythms.
Musicians themselves observe that a single mbira can produce the effect of two or more instruments being played simultaneously. One explanation for the apparent complexity of the music lies in a phenomenon known as "inherent rhythms." Inherent rhythms are those melodic rhythmic patterns not directly being played by the performer but arising from the total complex of the mbira music. They are the product of the psycho-acoustic fact that the ear does not perceive a series of tones as isolated pitches, but as a gestalt. For example, in mbira music in which the hands typically play large melodic leaps, the ear does not necessarily follow the precise linear melodic patterns being played; it picks out pitches of a similar level and groups them in separate independent phrases.Paul Berliner — The Soul of Mbira