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Chapter 2
NI-DSP Analysis VI Reference
NI-DSP SRM for LabVIEW for Windows
2-29
Part 3: NI-DSP Function Reference
DSP Equi-Ripple LowPass
Generates a lowpass FIR filter with equi-
ripple characteristics using the Parks-
McClellan algorithm and the number of
taps, pass frequency, stop frequency, and
sampling frequency. The VI then filters
the input sequence X to obtain the
lowpass filtered linear-phase sequence
Filtered Data.
ripple characteristics using the Parks-
McClellan algorithm and the number of
taps, pass frequency, stop frequency, and
sampling frequency. The VI then filters
the input sequence X to obtain the
lowpass filtered linear-phase sequence
Filtered Data.
The passband of the filter goes from zero
(DC) to pass freq. The transition band
goes from pass freq to stop freq, and
the stopband goes from stop freq to the
Nyquist frequency.
(DC) to pass freq. The transition band
goes from pass freq to stop freq, and
the stopband goes from stop freq to the
Nyquist frequency.
X is a DSP Handle Cluster that indicates the memory buffer on the DSP board that contains the input
data array.
data array.
# of Taps must be greater than 0. If the number of taps is less than or equal to zero, the VI returns an
error. # of Taps defaults to 31.
error. # of Taps defaults to 31.
pass freq must be greater than 0. If pass freq is less than or equal to zero, the VI returns an error. pass
freq defaults to 0.2.
freq defaults to 0.2.
stop freq must be greater than the pass freq and observe the Nyquist criterion:
0 < f
0
< f
1
≤
0.5f
s
,
where f
0
is the pass freq, f
1
is the stop freq, and f
s
is the sampling frequency. If any of these conditions
is violated, the VI returns an error. stop freq defaults to 0.3.
sampling freq: fs defaults to 1.0.
Filtered Data in is a DSP Handle Cluster that indicates the memory buffer on the DSP board that will
contain the filtered data output.
contain the filtered data output.
Filtered Data out is a DSP Handle Cluster that is identical to Filtered Data in, but with the filtered
data already stored in the memory buffer on the DSP board. Because the VI filters via convolution, the
number of elements, k, in Filtered Data out is:
data already stored in the memory buffer on the DSP board. Because the VI filters via convolution, the
number of elements, k, in Filtered Data out is:
k = n + m - 1,
where
n is the number of elements in X, and
m is the number of taps.
m is the number of taps.
A delay equal to
m-1
2
is also associated with the output sequence.
error in (no error) contains the error information from a previous VI. If an error occurs, it is passed out
error out and no other calls are made.
error out and no other calls are made.
error out contains the error information for this call.
The operation cannot be performed in place; that is, the input X and the output Filtered Data cannot be the same
DSP Handle Cluster.
DSP Handle Cluster.