/b_fill                              Fill ranges of sample value(s)

int     - buffer number
[
  int   - sample starting index
  int   - number of samples to fill (M)
  float - value
] * N

Set contiguous ranges of sample indices to single values. For each
range, the starting sample index is given followed by the number of
samples to change, followed by the value to fill. This is only meant
for setting a few samples, not whole buffers or large sections.