dsp.HighpassFilter
FIR or IIR highpass filter
Description
The dsp.HighpassFilter
System object™ independently filters each channel of the input over time using the given design
specifications. You can set the FilterType
property of
dsp.HighpassFilter
to 'FIR'
or 'IIR'
to implement the object as an FIR or IIR highpass filter.
When the FilterType
property is set to 'FIR'
,
using this object is an alternative to using the firceqrip
and
firgr
functions with dsp.FIRFilter
. The
dsp.HighpassFilter
object condenses the two-step process into one. You can
use measure
to verify that the design meets the prescribed specifications.
To filter each channel of your input:
Create the
dsp.HighpassFilter
object and set its properties.Call the object with arguments, as if it were a function.
To learn more about how System objects work, see What Are System Objects?
This object supports C/C++ code generation and SIMD code generation under certain conditions. This object also supports code generation for ARM® Cortex®-M and ARM Cortex-A processors. For more information, see Code Generation.
Creation
Description
returns a minimum
order FIR highpass filter, HPF
= dsp.HighpassFilterHPF
, with the default filter settings.
Calling the object with the default property settings filters the input data with a
stopband frequency of 8
kHz, a passband frequency of
12
kHz, a stopband attenuation of 80
dB, and a
passband ripple of 0.1
dB.
returns a highpass filter with additional properties specified by one or more
HPF
= dsp.HighpassFilter(Name=Value
)Name-Value
pair arguments. Name
is the
property name and Value
is the corresponding value. For example,
StopbandFrequency=8000
sets the stopband frequency specification of
the filter to 8000 Hz.
Properties
Unless otherwise indicated, properties are nontunable, which means you cannot change their
values after calling the object. Objects lock when you call them, and the
release
function unlocks them.
If a property is tunable, you can change its value at any time.
For more information on changing property values, see System Design in MATLAB Using System Objects.
FilterType
— Filter type
'FIR'
(default) | 'IIR'
Filter type, specified as one of these options:
'FIR'
— The object designs an FIR highpass filter.'IIR'
— The object designs an IIR highpass (biquad) filter.
DesignForMinimumOrder
— Flag to design minimum order filter
true
(default) | false
Flag to design minimum order filter, specified as:
true
–– The object designs the minimum order filter that meets the filter design specifications.false
–– The object designs the filter with the order that you specify in theFilterOrder
property.
FilterOrder
— Order of the FIR or IIR filter
50
(default) | positive integer
Order of the FIR or IIR filter, specified as a positive integer.
Dependencies
To enable this property, set DesignForMinimumOrder
to
false
.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
StopbandFrequency
— Filter stopband edge frequency
8000
(default) | real positive scalar
Filter stopband edge frequency, specified as a real positive scalar in Hz or in normalized frequency units (since R2023a).
If you set the
NormalizedFrequency
property to:
false
–– The value of the stopband edge frequency is in Hz. The value must be less than the passband edge frequency and half theSampleRate
property value.true
–– The value of the stopband edge frequency is in normalized frequency units. The value must be a positive scalar less than the passband edge frequency and less than1.0
.
(since R2023a)
Dependencies
To enable this property, set the DesignForMinimumOrder
property to true
.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
PassbandFrequency
— Filter passband edge frequency
12000
(default) | real positive scalar
Filter passband edge frequency, specified as a real positive scalar in Hz or in normalized frequency units (since R2023a).
If you set the
NormalizedFrequency
property to:
false
–– The value of the passband edge frequency is in Hz. The value must be less than half theSampleRate
property value and greater than theStopbandFrequency
property value.true
–– The value of the passband edge frequency is in normalized frequency units. The value must be a positive scalar less than1.0
and greater than theStopbandFrequency
property value.
(since R2023a)
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
StopbandAttenuation
— Minimum attenuation in the stopband
80
(default) | real positive scalar
Minimum attenuation in the stopband, specified as a real positive scalar in dB.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
PassbandRipple
— Maximum ripple of filter response in the passband
0.1
(default) | real positive scalar
Maximum ripple of filter response in the passband, specified as a real positive scalar in dB.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
NormalizedFrequency
— Flag to set frequencies in normalized units
false
(default) | true
Since R2023a
Flag to set frequencies in normalized units, specified as one of these values:
true
–– The passband edge and stopband edge frequencies must be in the normalized frequency units and less than1.0
.false
–– The passband edge and stopband edge frequencies are in Hz. You can specify the input sample rate through theSampleRate
property.
Data Types: logical
SampleRate
— Input sample rate
44100
(default) | positive real scalar
Input sample rate in Hz, specified as a positive real scalar.
Dependency
To enable this property, set
NormalizedFrequency
to false
. (since R2023a)
Data Types: single
| double
RoundingMethod
— Rounding method for output fixed-point operations
'Floor'
(default) | 'Ceiling'
| 'Convergent'
| 'Nearest'
| 'Round'
| 'Simplest'
| 'Zero'
Rounding method for output fixed-point operations, specified as a character vector. For more information on the rounding modes, see Precision and Range.
CoefficientsDataType
— Word and fraction lengths of coefficients
numerictype([],16)
(default) | numerictype
object
Word and fraction lengths of coefficients, specified as a
numerictype
object. The default,
numerictype(1,16)
corresponds to a signed numeric type object with
16-bit coefficients and a fraction length determined based on the coefficient values, to
give the best possible precision.
This property is not tunable.
Word length of the output is same as the word length of the input. Fraction length of the output is computed such that the entire dynamic range of the output can be represented without overflow. For details on how the fraction length of the output is computed, see Fixed-Point Precision Rules for Avoiding Overflow in FIR Filters.
Usage
Syntax
Description
Input Arguments
x
— Noisy data input
vector | matrix
Noisy data input, specified as a vector or a matrix. If the input signal is a matrix, each column of the matrix is treated as an independent channel. The number of rows in the input signal denote the channel length. This object accepts variable-size inputs. After the object is locked, you can change the size of each input channel, but you cannot change the number of channels.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
| fi
Complex Number Support: Yes
Output Arguments
y
— Filtered output
vector | matrix
Filtered output, returned as a vector or a matrix. The output has the same size, data type, and complexity characteristics as the input.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
| fi
Complex Number Support: Yes
Object Functions
To use an object function, specify the
System object as the first input argument. For
example, to release system resources of a System object named obj
, use
this syntax:
release(obj)
Specific to dsp.HighpassFilter
freqz | Frequency response of discrete-time filter System object |
filterAnalyzer | Analyze filters with Filter Analyzer app |
impz | Impulse response of discrete-time filter System object |
info | Information about filter System object |
coeffs | Returns the filter System object coefficients in a structure |
cost | Estimate cost of implementing filter System object |
grpdelay | Group delay response of discrete-time filter System object |
outputDelay | Determine output delay of single-rate or multirate filter |
generatehdl | Generate HDL code for quantized DSP filter (requires Filter Design HDL Coder) |
measure | Measure frequency response characteristics of filter System object |
Examples
Impulse and Frequency Response of FIR and IIR Highpass Filters
Create a minimum order FIR highpass filter for data sampled at 44.1 kHz. Specify a passband frequency of 12 kHz, a stopband frequency of 8 kHz, a passband ripple of 0.1 dB, and a stopband attenuation of 80 dB.
Fs = 44.1e3; filtertype = 'FIR'; Fpass = 12e3; Fstop = 8e3; Rp = 0.1; Astop = 80; FIRHPF = dsp.HighpassFilter(SampleRate=Fs,... FilterType=filtertype,... PassbandFrequency=Fpass,... StopbandFrequency=Fstop,... PassbandRipple=Rp,... StopbandAttenuation=Astop);
Design a minimum order IIR highpass filter with the same properties as the FIR highpass filter. Use clone
to create a system object with the same properties as the FIR Highpass filter. Change the FilterType
property of the cloned filter to IIR
.
IIRHPF = clone(FIRHPF);
IIRHPF.FilterType = 'IIR';
Plot the impulse response of the FIR highpass filter. The zeroth order coefficient is delayed by 19 samples, which is equal to the group delay of the filter. The FIR highpass filter is a causal FIR filter
impz(FIRHPF)
Plot the impulse response of the IIR highpass filter.
impz(IIRHPF)
Plot the magnitude and phase response of the FIR highpass filter.
freqz(FIRHPF)
Plot the magnitude and phase response of the IIR highpass filter.
freqz(IIRHPF)
Calculate the cost of implementing the FIR highpass filter.
cost(FIRHPF)
ans = struct with fields:
NumCoefficients: 39
NumStates: 38
MultiplicationsPerInputSample: 39
AdditionsPerInputSample: 38
Calculate the cost of implementing the IIR highpass filter. The IIR filter is more efficient to implement than its FIR counterpart.
cost(IIRHPF)
ans = struct with fields:
NumCoefficients: 18
NumStates: 14
MultiplicationsPerInputSample: 18
AdditionsPerInputSample: 14
Calculate the group delay of the FIR highpass filter.
grpdelay(FIRHPF)
Calculate the group delay of the IIR highpass filter. The FIR filter has a constant group delay (linear phase) while its IIR counterpart does not.
grpdelay(IIRHPF)
Filter White Gaussian Noise Signal with FIR Highpass Filter
Create a highpass filter using the dsp.HighpassFilter
object. Setting the NormalizedFrequency
property to true
designs the filter with frequency specifications in normalized frequency units.
LPF = dsp.HighpassFilter(NormalizedFrequency=true)
LPF = dsp.HighpassFilter with properties: FilterType: 'FIR' DesignForMinimumOrder: true StopbandFrequency: 0.3628 PassbandFrequency: 0.5442 StopbandAttenuation: 80 PassbandRipple: 0.1000 NormalizedFrequency: true Use get to show all properties
Create a spectrumAnalyzer
object to visualize the input and output signal spectra. With a sample rate of 44.1e3 Hz, the stopband frequency and the passband frequency of the filter translate to 8000 Hz and 12000 Hz, respectively.
SA = spectrumAnalyzer(SampleRate=44.1e3,... PlotAsTwoSidedSpectrum=false,ShowLegend=true,... YLimits=[-150 30],... Title='Input Signal and Output Signal of Lowpass Filter'); SA.ChannelNames = {'Input','Output'};
Run the highpass filter algorithm to filter the white Gaussian noisy input signal. View the input and output signals using the spectrum analyzer.
for k = 1:100 Input = randn(1024,1); Output = LPF(Input); SA([Input,Output]); end
Filter White Gaussian Noise with an IIR Highpass Filter
Set up the IIR highpass filter. The sampling rate of the white Gaussian noise is 44,100 Hz. The passband frequency of the filter is 12 kHz, the stopband frequency is 8 kHz, the passband ripple is 0.1 dB, and the stopband attenuation is 80 dB.
Fs = 44.1e3; filtertype = 'IIR'; Fpass = 12e3; Fstop = 8e3; Rp = 0.1; Astop = 80; hpf = dsp.HighpassFilter(SampleRate=Fs,... FilterType=filtertype,... PassbandFrequency=Fpass,... StopbandFrequency=Fstop,... PassbandRipple=Rp,... StopbandAttenuation=Astop);
View the magnitude response of the highpass filter.
filterAnalyzer(hpf)
Create a spectrum analyzer object.
sa = spectrumAnalyzer(SampleRate=44.1e3,... PlotAsTwoSidedSpectrum=false,ShowLegend=true,... YLimits=[-150 30],... Title='Input Signal and Output Signal of IIR Highpass Filter'); sa.ChannelNames = {'Input','Output'};
Filter the white Gaussian noisy input signal. View the input and output signals using the spectrum analyzer.
for k = 1:100 Input = randn(1024,1); Output = hpf(Input); sa([Input,Output]); end
Measure Frequency Response Characteristics of Highpass Filter
Measure the frequency response characteristics of a highpass filter. Create a dsp.HighpassFilter
System object with default properties. Measure the frequency response characteristics of the filter.
HPF = dsp.HighpassFilter
HPF = dsp.HighpassFilter with properties: FilterType: 'FIR' DesignForMinimumOrder: true StopbandFrequency: 8000 PassbandFrequency: 12000 StopbandAttenuation: 80 PassbandRipple: 0.1000 NormalizedFrequency: false SampleRate: 44100 Use get to show all properties
HPFMeas = measure(HPF)
HPFMeas = Sample Rate : 44.1 kHz Stopband Edge : 8 kHz 6-dB Point : 10.418 kHz 3-dB Point : 10.8594 kHz Passband Edge : 12 kHz Stopband Atten. : 81.8558 dB Passband Ripple : 0.08066 dB Transition Width : 4 kHz
Algorithms
FIR Highpass Filter
For the minimum order design, the algorithm uses generalized Remez FIR filter design algorithm. For the specified order design, the algorithm uses the constrained equiripple FIR filter design algorithm. The designed filter is then implemented as a linear phase Type-1 filter with a Direct form
structure.
IIR Highpass Filter
In the IIR configuration, the algorithm uses the elliptic design method to compute the SOS and scale values required to meet the filter design specifications. The algorithm uses the SOS and scale values to setup a Direct form I
biquadratic IIR filter, which forms the basis of the IIR version of the highpass filter.
References
[1] Shpak, D.J., and A. Antoniou. "A generalized Remez method for the design of FIR digital filters." IEEE® Transactions on Circuits and Systems. Vol. 37, Issue 2, Feb. 1990, pp. 161–174.
[2] Selesnick, I.W., and C. S. Burrus. "Exchange algorithms that complement the Parks-McClellan algorithm for linear-phase FIR filter design." IEEE Transactions on Circuits and Systems. Vol. 44, Issue 2, Feb. 1997, pp. 137–143.
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.
Usage notes and limitations:
See System Objects in MATLAB Code Generation (MATLAB Coder).
This object supports code generation for ARM Cortex-M and ARM Cortex-A processors. To learn more about ARM Cortex code generation, see Code Generation for ARM Cortex-M and ARM Cortex-A Processors.
This object also supports SIMD code generation using Intel® AVX2 code replacement library under these conditions:
FilterType
is set to'FIR'
.Input signal has a data type of
single
ordouble
.
The SIMD technology significantly improves the performance of the generated code. For more information, see SIMD Code Generation. To generate SIMD code from this object, see Use Intel AVX2 Code Replacement Library to Generate SIMD Code from MATLAB Algorithms.
HDL Code Generation
Generate VHDL, Verilog and SystemVerilog code for FPGA and ASIC designs using HDL Coder™.
This object supports HDL code generation with the Filter Design HDL Coder™ product. For workflows and limitations, see Generate HDL Code for Filter System Objects (Filter Design HDL Coder).
Version History
Introduced in R2015aR2023a: Support for normalized frequencies
When you set the NormalizedFrequency
property to
true
, you must specify the passband and stopband frequencies in
normalized frequency units (0 to 1).
When you set the NormalizedFrequency
property to
true
while creating the object, the passband and stopband frequency
values are automatically set to normalized frequency units using the default sample rate of
44100 Hz.
hpFilter = dsp.HighpassFilter(NormalizedFrequency=true)
hpFilter = dsp.HighpassFilter with properties: FilterType: 'FIR' DesignForMinimumOrder: true StopbandFrequency: 0.3628 PassbandFrequency: 0.5442 StopbandAttenuation: 80 PassbandRipple: 0.1000 NormalizedFrequency: true
When you set the NormalizedFrequency
property to
true
after you create the object, the passband and stopband frequencies
must be manually set to the normalized frequency values before you run the object
algorithm.
hpFilter = dsp.HighpassFilter
hpFilter = dsp.HighpassFilter with properties: FilterType: 'FIR' DesignForMinimumOrder: true StopbandFrequency: 8000 PassbandFrequency: 12000 StopbandAttenuation: 80 PassbandRipple: 0.1000 NormalizedFrequency: false SampleRate: 44100
NormalizedFrequency
to
true
and manually convert the frequency values in Hz to normalized
values using the input sample rate in Hz. For example, if the input sample rate is 44100 Hz,
the corresponding values in normalized units are computed using these equations.hpFilter.NormalizedFrequency = true; hpFilter.StopbandFrequency = 8000/(44100/2); hpFilter.PassbandFrequency = 12000/(44100/2)
hpFilter = dsp.HighpassFilter with properties: FilterType: 'FIR' DesignForMinimumOrder: true StopbandFrequency: 0.3628 PassbandFrequency: 0.5442 StopbandAttenuation: 80 PassbandRipple: 0.1000 NormalizedFrequency: true
See Also
Functions
freqz
|filterAnalyzer
|impz
|info
|coeffs
|cost
|grpdelay
|outputDelay
|generatehdl
|measure
|firceqrip
|firgr
Objects
Blocks
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