Upsample the signal by an integer factor: factor-1 zero-value
samples are inserted between each pair of input samples. As a
result, the original spectrum is replicated into the new frequency
space (imaging) and attenuated. This attenuation can be
compensated for by adding vol factor after any further processing.
The upsample effect is typically used in combination with
filtering effects.
For a general resampling effect with anti-imaging, see rate.
See also downsample.