Page 42 - Summer 2007

Fig. 5b. Time series of shuffle rhythm.
Fig. 5c. DIFFDOT plot of shuffle rhythm.
lessly. Overall, this contributes to the flowing feel that many Brazilian songs have.
The spectrogram in Figs. 5 and 5a shows a shuffle pattern played by a surdo (Brazilian bass drum) and an afoxe (gourd instrument with a stick scraping across it). The audio spectrum is quite diffuse, although note events can be identified. The time series plot, Fig. 5b shows considerable complexity of the waveforms in all frequency bands due to the instrument’s timbre—a stick scraping across the grooves in the gourd produc- ing many correlated closely spaced click- ing sounds which spread across many frequencies in a fairly non-harmonic fashion. The pulse in the low frequency is played by the surdo. The DIFFDOT plot, Fig. 5c shows swinghee timing variations in both the pulse and secondary events tracks. Like Graceland, the two rhythms are closely connected but playing the Swing in different ways.
Ensemble swing in Brazilian swinghee
In this section an example of complex interaction between two instruments will be examined in some detail. The pandeiro plays a duet with a tamborim, a small Brazilian hand drum generally hit with a stick. The tamborim plays many of the most complex rhythms in a Samba. The basic rhythms are often difficult, and the interpretive timing is very fine-grained and precise, typically 10 to 20 millisecond excursions from canonical beat locations.
Figure 6 shows the pulse played by the pandeiro, and the desinha (design, a Brazilian term for complex rhythmic orna- ment) played by the tamborim. In the upper plot when the tamborim starts playing, it is not at the standard beginning of the batida. Instead the drummer plays a variation on a por- tion of the second half of the entire tamborim phrase, which leads into the downbeat. The downbeat is indicated by the green marker at time location 1700, except that there is a fur- ther variation—it is not the primary downbeat but the off- beat, so the tamborim is playing on the opposite side from the pandeiro. It is very common in Brazilian music for some
Brazilian swinghee 2: Shuffle
Many percussion and drum note events have a very sharp and precise onset, making them easy to identify by our approach while others have a much less precise sound. The term “shuffle” is used to describe a wide range of Swing rhythms played in this style. Shakers, brushes on a snare drum or hi-hat cymbal, afoxe and guiro are all examples of shuffle instruments. Single note events from these instru- ments can be identified, but overall there is a feeling of blur- ring and blending of each note event into the next. The meter and subdivision of the rhythm is defined by the loudness peaks which are identifiable but somewhat temporally ambiguous events. Shuffle is an odd combination of vague- ness and precision, difficult to describe with language.
Identification of note events is more difficult for these less precise musical events, and marking the onset time locations precisely can be subject to interpretation of how the rhythm feels. The peak power was chosen to be used as the location of the note event,
although perceptually there is some
activity happening before the peak,
unlike most percussion sounds with
their fast onset. The standard
Brazilian ganza (shaker) rhythm usu-
ally has a noticeable snap that pre-
cedes the downbeat and this snap is
fairly sharp, but the remaining notes
are more blurry. The snap gives a pre-
cise anchor to the rhythm which
makes the blurry parts sound well
integrated to the ensemble Swing,
rather than sounding as if played care-
Fig. 6. Pandeiro pulse and tamborim desinha.
40 Acoustics Today, July 2007