User`s guide

FIR Rate Conversion
5-208
Frame-Based Operation
This block accepts only frame-based inputs. An M
i
-by-N frame-based matrix
input is treated as N independent channels, and the block resamples each
channel independently over time.
The
Interpolation factor, L, and Decimation factor, K, must satisfy the
relation
for an integer output frame size M
o
. The simplest way to satisfy this
requirement is to let the
Decimation factor equal the input frame size, M
i
.
The output frame size, M
o
, is then equal to the Interpolation factor. This
change in the frame size, from M
i
to M
o
, produces the desired rate conversion
while leaving the output frame period the same as the input (T
fo
=T
fi
).
Latency
The FIR Rate Conversion block has no tasking latency. The block propagates
the first filtered input (received at t=0) as the first output sample.
Examples The dspsrcnv demo compares sample rate conversion performed by the FIR
Rate Conversion block with the same conversion performed by a cascade of
Upsample, Direct-Form II Transpose Filter, and Downsample blocks.
K
L
----
M
i
M
o
--------=
17
18
19
20
13
14
15
16
9
10
11
12
5
6
7
8
1
2
3
4
t=0t=6t=12 t=9 t=3
first input frame
T
fi
= 3
first non-zero output
3.84
4.30
4.72
2.50
2.94
3.39
1.17
1.61
2.05
0.04
0.29
0.72
t=0t=6t=9 t=3
T
fo
= 3
5.17
5.61
6.05
t=12
FIR Rate Conversion (One-channel input)
Decimation factor: 4
Interpolation factor: 3
Input:
4-by-1
T
fi
= 3
Output:
3-by-1
T
fo
= 3