Polyphase FIR interpolator
The FIRInterpolator
object upsamples an input
by the integer upsampling factor, L, followed by
an FIR antiimaging filter. The filter coefficients are scaled by
the interpolation factor. A polyphase interpolation structure implements
the filter. The resulting discretetime signal has a sampling rate L times
the original sampling rate.
To upsample an input:
Define and set up your FIR interpolator. See Construction.
Call step
to upsample the input according
to the properties of dsp.FIRInterpolator
. 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.
firinterp = dsp.FIRInterpolator
returns
an FIR interpolator, firinterp
, which upsamples an
input signal by a factor of 3 and applies an FIR filter to interpolate
the output.
firinterp = dsp.FIRInterpolator('
returns an FIR interpolator, PropertyName
',PropertyValue
,
...)firinterp
,
with each property set to the specified value.
firinterp = dsp.FIRInterpolator(INTERP,
NUM,'
returns an FIR interpolation object, PropertyName
',PropertyValue
,
...)firinterp
,
with the InterpolationFactor
property set to INTERP
,
the Numerator
property set to NUM
,
and other properties set to the specified values.

Interpolation factor Specify the integer factor, L, by which to increase the sampling rate of the input signal. The polyphase implementation uses L polyphase subfilters to compute convolutions at the lower sample rate. The FIR interpolator delays and interleaves these lowerrate convolutions to obtain the higherrate output. The property value defaults to 3. 

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

FIR filter coefficients Specify the numerator coefficients of the FIR antiimaging filter as the coefficients of a polynomial in z^{–1}. Indexing from zero, the filter coefficients are: $$H(z)={\displaystyle \sum _{n=0}^{N1}b}(n){z}^{n}$$ InterpolationFactor property before filtering the signal. To
form the L polyphase subfilters, Numerator is appended with zeros if necessary. The default is
the output of fir1(15,0.25) . This property is valid only
when the NumeratorSource property is
'Property' .

freqz  Frequency response 
fvtool  Open filter visualization tool 
impz  Impulse response 
phasez  Unwrapped phase response 
reset  Reset FIR interpolator filter states 
step  Upsample and interpolate input 
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 Interpolation block reference page. The object properties correspond to the block parameters, except:
The FIRInterpolator
object does not
have a property that corresponds to the Input processing parameter
of the FIR Interpolation block.
The Rate options block parameter
is not supported by the FIRInterpolator
object.