An electronic percussion instrument samples an input waveform. An unused waveform number may be automatically assigned to the sampled waveform upon sampling or when a user-specified waveform number is already in use for another waveform. Musical time parameters for the input waveform may be specified in advance of sampling, and an endpoint for the sampled waveform may be automatically set in response to a stop sampling command so that length of the waveform is a whole number of musical time units such as bars or beats. The endpoint of the sampled waveform may be set to the beginning or the end of the musical time unit during which the stop command is received, depending on the time at which the stop command is received. The sampled waveform may be edited by manually moving the starting point by a specified amount and automatically moving the end point by a corresponding amount, by changing the specified tempo of the waveform, or by specifying a different number of musical time units.