Linear interpolator
hm = mfilt.linearinterp(l)
hm = mfilt.linearinterp(l)
returns
an FIR linear interpolator hm
with an integer interpolation
factor l
. Provide l
as a positive
integer. The default value for the interpolation factor is 2 when
you do not include the input argument l
.
When you use this linear interpolator, the samples added to
the input signal have values between the values of adjacent samples
in the original signal. Thus you see something like a smooth profile
where the interpolated samples continue a line between the previous
and next original samples. The example demonstrates this smooth profile
clearly. Compare this to the interpolation process for mfilt.holdinterp
,
which creates a stairstep profile.
Make this filter a fixedpoint or singleprecision filter by
changing the value of the Arithmetic
property for
the filter hm
as follows:
To change to singleprecision filtering, enter
set(hm,'arithmetic','single');
To change to fixedpoint filtering, enter
set(hm,'arithmetic','fixed');
The following table describes the input argument for mfilt.linearinterp
.
Input Argument  Description 

 Interpolation factor for the filter. 
This section describes the properties for both floatingpoint filters (doubleprecision and singleprecision) and fixedpoint filters.
Every multirate filter object has properties that govern the
way it behaves when you use it. Note that many of the properties are
also input arguments for creating mfilt.linearinterp
objects.
The next table describes each property for an mfilt.linearinterp
filter
object.
Name  Values  Description 


 Specifies the arithmetic the filter uses to process data while filtering. 
 String  Reports the type of filter object. You cannot set this
property — it is always read only and results from your choice
of 
 Integer  Interpolation factor for the filter. 
 '  Determine whether the filter states get restored to zero for each filtering operation 
 Double or single array  Filter states. 
This table shows the properties associated with the fixedpoint
implementation of the mfilt.holdinterp
filter.
Note The table lists all of the properties that a fixedpoint filter can have. Many of the properties listed are dynamic, meaning they exist only in response to the settings of other properties. To view all of the characteristics for a filter at any time, use info(hm) where 
For further information about the properties of this filter
or any mfilt
object, refer to Multirate Filter Properties.
Name  Values  Description 

 Any positive or negative integer number of bits. Depends on L. [29 when L=2]  Specifies the fraction length used to interpret data output by the accumulator. 
 Any integer number of bits [33]  Sets the word length used to store data in the accumulator. 
 fixed for fixedpoint filters  Setting this to 
 [true], false  Specifies whether the filter automatically chooses the
proper fraction length to represent filter coefficients without overflowing.
Turning this off by setting the value to 
 Any integer number of bits [16]  Specifies the word length to apply to filter coefficients. 
 [FullPrecision], SpecifyPrecision  Controls whether the filter automatically sets the output
word and fraction lengths, product word and fraction lengths, and
the accumulator word and fraction lengths to maintain the best precision
results during filtering. The default value, 
 Any positive or negative integer number of bits [15]  Specifies the fraction length the filter uses to interpret input data. 
 Any integer number of bits [16]  Specifies the word length applied to interpret input data. 
 Any positive or negative integer number of bits [  Sets the fraction length used to interpret the numerator coefficients. 
 Any positive or negative integer number of bits [29]  Determines how the filter interprets the filter output
data. You can change the value of 
 Any integer number of bits [33]  Determines the word length used for the output data.
You make this property editable by setting 
 saturate, [wrap]  Sets the mode used to respond to overflow conditions
in fixedpoint arithmetic. Choose from either 
 [  Sets the mode the filter uses to quantize numeric values when the values lie between representable values for the data format (word and fraction lengths).
The choice you make affects only the accumulator and output arithmetic. Coefficient and input arithmetic always round. Finally, products never overflow — they maintain full precision. 
 [true], false  Specifies whether the filter uses signed or unsigned fixedpoint coefficients. Only coefficients reflect this property setting. 

 Contains the filter states before, during, and after
filter operations. States act as filter memory between filtering runs
or sessions. The states use 
Linear interpolator structures depend on the FIR filter you use to implement the filter. By default, the structure is directform FIR.
Interpolation by a factor of 2 (used to convert the input signal sampling rate from 22.05 kHz to 44.1 kHz).
l = 2; % Interpolation factor hm = mfilt.linearinterp(l); fs = 22.05e3; % Original sample freq: 22.05 kHz. n = 0:5119; % 5120 samples, 0.232 second long signal x = sin(2*pi*1e3/fs*n); % Original signal, sinusoid at 1 kHz y = filter(hm,x); % 10240 samples, still 0.232 seconds stem(n(1:22)/fs,x(1:22),'filled') % Plot original sampled at % 22.05 kHz hold on % Plot interpolated signal (44.1 % kHz) in red stem(n(1:44)/(fs*l),y(2:45),'r') xlabel('Time (s)');ylabel('Signal Value')
Using linear interpolation, as compared to the hold approach
of mfilt.holdinterp
, provides greater fidelity
to the original signal.
mfilt.cicinterp
 mfilt.firinterp
 mfilt.firsrc
 mfilt.holdinterp