User`s guide

Downsample
5-141
5Downsample
Purpose Resample an input at a lower rate by deleting samples.
Library Signal Operations
Description The Downsample block resamples each channel of the M
i
-by-N input at a rate
K times lower than the input sample rate by discarding K-1 consecutive
samples following each sample passed through to the output. The integer K is
specified by the
Downsample factor parameter.
The
Sample offset parameter delays the output samples by an integer number
of sample periods, D, where 0 ≤ D < (K-1), so that any of the K possible output
phases can be selected. For example, when you downsample the sequence
1, 2, 3, ... by a factor of 4, you can select from the following four phases.
The initial zero in each output sequence above is a result of the default zero
Initial condition parameter setting for this example. See “Latency” on
page 5-143 for more on the
Initial condition parameter.
Sample-Based Operation
When the input is sample-based, the block treats each of the M∗N matrix
elements as an independent channel, and downsamples each channel over
time. The input and output sizes are identical.
The
Sample-based mode parameter determines how the block represents the
new rate at the output. There are two available options:
•
Allow multirate
When Allow multirate is selected, the sample period of the sample-based
output is K times longer than the input sample period (T
so
=KT
si
). The block
is therefore multirate.
Input Sequence Sample Offset, D Output Sequence (K=4)
1,2,3,... 0 0,1,5,9,13,17,21,25,...
1,2,3,... 1 0,2,6,10,14,18,22,26,...
1,2,3,... 2 0,3,7,11,15,19,23,27,...
1,2,3,... 3 0,4,8,12,16,20,24,28,...