Polyphase FIR decimator
The FIRDecimator
object resamples vector or
matrix inputs along the first dimension. The object reseamples at
a rate M times slower than the input sampling rate,
where M is the integervalued downsampling factor.
The decimation combines an FIR antialiasing filter with downsampling.
The FIR decimator object uses a polyphase implementation of the FIR
filter.
To resample vector or matrix inputs along the first dimension:
Define and set up your FIR decimator. See Construction.
Call step
to resample the vector
or matrix inputs according to the properties of dsp.FIRDecimator
.
The behavior of step
is specific to each object in
the toolbox.
Starting in R2016b, instead of using the step
method
to perform the operation defined by the System
object™, you can
call the object with arguments, as if it were a function. For example, y
= step(obj,x)
and y = obj(x)
perform
equivalent operations.
firdecim = dsp.FIRDecimator
returns
an FIR decimator, firdecim
, which applies an FIR
filter with a cutoff frequency of 0.4*pi
radians/sample
to the input and downsamples the filter output by factor of 2. This System
object supports
variablesize input.
firdecim = dsp.FIRDecimator
('
returns an FIR decimator, PropertyName'
,PropertyValue
,
...) firdecim
,
with each property set to the specified value.
firdecim = dsp.FIRDecimator(DECIM,
NUM, '
returns an FIR decimator, PropertyName
',PropertyValue
,
...)firdecim
,
with the integervalued DecimationFactor
property
set to DECIM
, the Numerator
property
set to NUM
, and other specified properties set
to the specified values.

Decimation factor Specify the downsampling factor as a positive integer. The FIR
decimator reduces the sampling rate of the input by this factor. The
size of the input along the first dimension must be a multiple of
the decimation factor. The default is 

FIR filter coefficient source Specify the source of the numerator coefficients as one of 

FIR filter coefficients Specify the numerator coefficients of the FIR filter in powers of z^{–1}. The following equation defines the system function for a filter of length L: $$H(z)={\displaystyle \sum _{l=0}^{L1}{b}_{l}}{z}^{l}$$ DecimationFactor .
You can specify the filter coefficients as a vector in the supported
data types. The default is fir1(35,0.4) .


Filter structure Specify the implementation of the FIR filter as either 
freqz  Frequency response 
fvtool  Open filter visualization tool 
impz  Impulse response 
phasez  Unwrapped phase response 
reset  Reset filter states of FIR decimator 
step  Decimate input by integer factor 
More Analysis Methods for Filter System Objects.
Common to All System Objects  

clone  Create System object with same property values 
getNumInputs  Expected number of inputs to a System object 
getNumOutputs  Expected number of outputs of a System object 
isLocked  Check locked states of a System object (logical) 
release  Allow System object property value changes 
This object implements the algorithm, inputs, and outputs described on the FIR Decimation block reference page. The object properties correspond to the block parameters, except:
Framing – The FIR decimator
object only supports Maintain input frame rate
Output buffer initial conditions – The FIR decimator object does not support this parameter.
Rate options – The FIR decimator object does not support this parameter.
Input processing The FIR decimator object does not support this parameter.