designVarSlopeFilter

Design variable slope lowpass or highpass IIR filter

Syntax

[B,A] =
designVarSlopeFilter(slope,Fc)

[B,A] =
designVarSlopeFilter(slope,Fc,type)

[B,A] =
designVarSlopeFilter(___,Name,Value)

Description

[B,A] = designVarSlopeFilter(slope,Fc) designs a lowpass filter with the specified slope and cutoff frequency. B and A are matrices of numerator and denominator coefficients, with columns corresponding to cascaded second-order sections (SOS).

example

[B,A] = designVarSlopeFilter(slope,Fc,type) specifies the design type as a lowpass or highpass filter.

example

[B,A] = designVarSlopeFilter(___,Name,Value) specifies options using one or more Name,Value pair arguments.

Examples

collapse all

Design Lowpass IIR Filter

Open Live Script

Design two second-order section (SOS) lowpass IIR filters using designVarSlopeFilter.

Specify the sampling frequency, slope, and normalized cutoff frequency for two lowpass IIR filters. The sampling frequency is in Hz. The slope is in dB/octave.

Fs = 48e3;

slope = 18;

Fc1 = 10e3/(Fs/2);
Fc2 = 16e3/(Fs/2);

Design the filter coefficients using the specified parameters.

[B1,A1] = designVarSlopeFilter(slope,Fc1,"Orientation","row");
[B2,A2] = designVarSlopeFilter(slope,Fc2,"Orientation","row");

Visualize your filter design.

filterAnalyzer(B1,A1,B2,A2,SampleRates=Fs,FrequencyScale="log")

Process Audio Using Lowpass Filter

Open Live Script

Design a second-order section (SOS) lowpass IIR filter using designVarSlopeFilter. Use your lowpass filter to process an audio signal.

Create audio file reader and audio device writer objects. Use the sample rate of the reader as the sample rate of the writer.

frameSize = 256;

fileReader = dsp.AudioFileReader( ...
    "RockGuitar-16-44p1-stereo-72secs.wav", ...
    SamplesPerFrame=frameSize);

sampleRate = fileReader.SampleRate;

deviceWriter = audioDeviceWriter( ...
    SampleRate=sampleRate);

Play the audio signal through your device.

count = 0;
while count < 2500
    audio = fileReader();
    deviceWriter(audio);
    count = count + 1;
end
reset(fileReader)

Design a lowpass filter with a 12 dB/octave slope and a 0.15 normalized cutoff frequency.

slope = 12;
cutoff = 0.15;
[B,A] = designVarSlopeFilter(slope,cutoff,Orientation="row");

Visualize your filter design.

[h,f] = freqz([B A],[],sampleRate);
plot(f/1000,mag2db(abs(h)))
grid
ylim([-75 5])
xlabel("Frequency (kHz)")
ylabel("Magnitude Response (dB)")

Figure contains an axes object. The axes object with xlabel Frequency (kHz), ylabel Magnitude Response (dB) contains an object of type line.

Create an SOS filter.

myFilter = dsp.SOSFilter(B,A);

Create a spectrum analyzer to visualize the original audio signal and the audio signal passed through your lowpass filter.

scope = spectrumAnalyzer( ...
    SampleRate=sampleRate, ...
    PlotAsTwoSidedSpectrum=false, ...
    FrequencyScale="log", ...
    Title="Original and Equalized Signal", ...
    ShowLegend=true, ...
    ChannelNames={'Original Signal','Filtered Signal'});

Play the filtered audio signal and visualize the original and filtered spectrums.

count = 0;
while count < 2500
    originalSignal = fileReader();
    filteredSignal = myFilter(originalSignal);
    scope([originalSignal(:,1),filteredSignal(:,1)]);
    deviceWriter(filteredSignal);
    count = count + 1;
end

As a best practice, release your objects once done.

release(deviceWriter)
release(fileReader)
release(scope)

Design Highpass IIR Filter

Open Live Script

Design two second-order section (SOS) highpass IIR filters using designVarSlopeFilter.

Specify the sampling frequency in Hz, the slope in dB/octave, and the normalized cutoff frequency.

Fs = 48e3;
slope1 = 18;
slope2 = 36;
Fc = 4000/(Fs/2);

Design the filter coefficients using the specified parameters.

[B1,A1] = designVarSlopeFilter(slope1,Fc,"hi",Orientation="row");
[B2,A2] = designVarSlopeFilter(slope2,Fc,"hi",Orientation="row");

Visualize your filter design.

filterAnalyzer(B1,A1,B2,A2,...
       SampleRates=Fs,...
       FrequencyScale="log")

Diminish Plosives from Speech Signal

Open Live Script

Plosives are consonant sounds resulting from a sudden release of airflow. They are most pronounced in words beginning with p, d, and g sounds. Plosives can be emphasized by the recording process and are often displeasurable to hear. In this example, you minimize the plosives of a speech signal by applying highpass filtering and low-band compression.

Create a dsp.AudioFileReader object and a audioDeviceWriter object to read an audio signal from a file and write an audio signal to a device. Play the unprocessed signal. Then release the file reader and device writer.

fileReader = dsp.AudioFileReader('audioPlosives.wav');
deviceWriter = audioDeviceWriter('SampleRate',fileReader.SampleRate);

while ~isDone(fileReader)
    audioIn = fileReader();
    deviceWriter(audioIn);
end
release(deviceWriter)
release(fileReader)

Design a highpass filter with a steep rolloff of all frequencies below 120 Hz. Use a dsp.SOSFilter object to implement the highpass filter design. Create a crossover filter with one crossover at 250 Hz. The crossover filter enables you to separate the band of interest for processing. Create a dynamic range compressor to compress the dynamic range of plosive sounds. To apply no make-up gain, set the MakeUpGainMode to "Property" and use the default 0 dB MakeUpGain property value. Create a time scope to visualize the processed and unprocessed audio signal.

[B,A] = designVarSlopeFilter(48,120/(fileReader.SampleRate/2),"hi",Orientation="row");
biquadFilter = dsp.SOSFilter(B,A);

crossFilt = crossoverFilter( ...
    "SampleRate",fileReader.SampleRate, ...
    "NumCrossovers",1, ...
    "CrossoverFrequencies",250, ...
    "CrossoverSlopes",48);

dRCompressor = compressor( ...
    "Threshold",-35, ...
    "Ratio",10, ...
    "KneeWidth",20, ...
    "AttackTime",1e-4, ...
    "ReleaseTime",3e-1, ...
    "MakeUpGainMode","Property", ...
    "SampleRate",fileReader.SampleRate);

scope = timescope( ...
    "SampleRate",fileReader.SampleRate, ...
    "TimeSpanSource","property","TimeSpan",3, ...
    "BufferLength",fileReader.SampleRate*3*2, ...
    "YLimits",[-1 1], ...
    "ShowGrid",true, ...
    "ShowLegend",true, ...
    "ChannelNames",{'Original','Processed'});

In an audio stream loop:

Read in a frame of the audio file.
Apply highpass filtering using your biquad filter.
Split the audio signal into two bands.
Apply dynamic range compression to the lower band.
Remix the channels.
Write the processed audio signal to your audio device for listening.
Visualize the processed and unprocessed signals on a time scope.

As a best practice, release your objects once done.

while ~isDone(fileReader)
    audioIn = fileReader();
    audioIn = biquadFilter(audioIn);
    [band1,band2] = crossFilt(audioIn);
    band1compressed = dRCompressor(band1);
    audioOut = band1compressed + band2;
    deviceWriter(audioOut);
    scope([audioIn audioOut])
end

As a best practice, release your objects once done.

release(deviceWriter)
release(fileReader)
release(crossFilt)
release(dRCompressor)
release(scope)

Input Arguments

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`slope` — Filter slope (dB/octave)
real scalar in the range [0:6:48]

Filter slope in dB/octave, specified as a real scalar in the range [0:6:48]. Values that are not multiples of 6 are rounded.

`Fc` — Normalized cutoff frequency
real scalar in the range 0 to 1

Normalized cutoff frequency, specified as a real scalar in the range 0 to 1, where 1 corresponds to the Nyquist frequency (π rad/sample).

`type` — Filter type
`'lo'` (default) | `'hi'`

Filter type, specified as 'lo' or 'hi'.

'lo'–– Lowpass filter
'hi'–– Highpass filter

Data Types: char | string

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: 'Orientation',"row"

`Orientation` — Orientation of returned filter coefficients
`"column"` (default) | `"row"`

Orientation of returned filter coefficients, specified as the comma-separated pair consisting of 'Orientation' and "column" or "row".

Data Types: char | string

Output Arguments

collapse all

`B` — Numerator filter coefficients
3-by-4 matrix | 4-by-3 matrix

Numerator filter coefficients, returned as a matrix. The size and interpretation of B depends on the Orientation:

If 'Orientation' is set to "column", then B is returned as a 3-by-4 matrix. Each column of B corresponds to the numerator coefficients of a different second-order section of your cascaded IIR filter.
If 'Orientation' is set to "row", then B is returned as a 4-by-3 matrix. Each row of B corresponds to the numerator coefficients of a different second-order section of your cascaded IIR filter.

`A` — Denominator filter coefficients
2-by-4 matrix | 4-by-3 matrix

Denominator filter coefficients, returned as a matrix. The size and interpretation of A depends on the Orientation:

If 'Orientation' is set to "column", then A is returned as a 2-by-4 matrix. Each column of A corresponds to the denominator coefficients of a different second-order section of your cascaded IIR filter. A does not include the leading unity coefficient for each section.
If 'Orientation' is set to "row", then B is returned as a 4-by-3 matrix. Each row of B corresponds to the denominator coefficients of a different second-order section of your cascaded IIR filter.

References

[1] Orfanidis, Sophocles J. "High-Order Digital Parametric Equalizer Design." Journal of the Audio Engineering Society. Vol. 53, November 2005, pp. 1026–1046.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2016a

expand all

R2024b: Warning that filter design functions will return coefficients in row orientation by default

The designVarSlopeFilter, designParamEQ, and designShelvingEQ functions will return filter coefficients in row orientation by default in a future release. With row orientation, the functions return the coefficients as matrices where each row contains the coefficients of the corresponding second-order section of the filter.

The default value of the Orientation name-value argument, "column", will be removed in a future release and throws a warning in R2024b. Set Orientation to "row" to return coefficients in row orientation in the current release.

R2024a: Filter design functions will return coefficients in row orientation by default

The designVarSlopeFilter, designParamEQ, and designShelvingEQ functions will return filter coefficients in row orientation by default in a future release.

designVarSlopeFilter

Syntax

Description

Examples

Design Lowpass IIR Filter

Process Audio Using Lowpass Filter

Design Highpass IIR Filter

Diminish Plosives from Speech Signal

Input Arguments

`slope` — Filter slope (dB/octave)
real scalar in the range [0:6:48]

`Fc` — Normalized cutoff frequency
real scalar in the range 0 to 1

`type` — Filter type
`'lo'` (default) | `'hi'`

Name-Value Arguments

`Orientation` — Orientation of returned filter coefficients
`"column"` (default) | `"row"`

Output Arguments

`B` — Numerator filter coefficients
3-by-4 matrix | 4-by-3 matrix

`A` — Denominator filter coefficients
2-by-4 matrix | 4-by-3 matrix

References

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

R2024b: Warning that filter design functions will return coefficients in row orientation by default

R2024a: Filter design functions will return coefficients in row orientation by default

See Also

Topics

designVarSlopeFilter

Syntax

Description

Examples

Design Lowpass IIR Filter

Process Audio Using Lowpass Filter

Design Highpass IIR Filter

Diminish Plosives from Speech Signal

Input Arguments

slope — Filter slope (dB/octave) real scalar in the range [0:6:48]

Fc — Normalized cutoff frequency real scalar in the range 0 to 1

type — Filter type 'lo' (default) | 'hi'

Name-Value Arguments

Orientation — Orientation of returned filter coefficients "column" (default) | "row"

Output Arguments

B — Numerator filter coefficients 3-by-4 matrix | 4-by-3 matrix

A — Denominator filter coefficients 2-by-4 matrix | 4-by-3 matrix

References

Extended Capabilities

C/C++ Code Generation Generate C and C++ code using MATLAB® Coder™.

Version History

R2024b: Warning that filter design functions will return coefficients in row orientation by default

R2024a: Filter design functions will return coefficients in row orientation by default

See Also

Topics

`slope` — Filter slope (dB/octave)
real scalar in the range [0:6:48]

`Fc` — Normalized cutoff frequency
real scalar in the range 0 to 1

`type` — Filter type
`'lo'` (default) | `'hi'`

`Orientation` — Orientation of returned filter coefficients
`"column"` (default) | `"row"`

`B` — Numerator filter coefficients
3-by-4 matrix | 4-by-3 matrix

`A` — Denominator filter coefficients
2-by-4 matrix | 4-by-3 matrix

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.