Boss BR-1200CD Owner's Manual page 61

Selecting drums to act as a guide for recording
A short period of time (i.e., 1 or 2 seconds) is required for the switching of drum kits. Although you will not be able to
hear the drum pattern during this period, this is normal and is not the result of a malfunction.
Although this section described a playback method where a basic rhythm (Drum Pattern) of one or several bars in
length was repeated indefinitely, you can also arrange and play back drum patterns that have been matched to a song
structure comprising Intro, Verse, Fill, Bridge, Break, and End Crash elements in any order. This type of combination
is referred to as a "rhythm arrangement." For more detailed information regarding rhythm arrangement operations,
refer to "Using rhythm arrangements" (p. 197).
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