scattergram

Visualize joint time-frequency scattering coefficients

Since R2024b

Syntax

scattergram(jtfn,cfs,meta)

scattergram(___,Name=Value)

Description

scattergram(jtfn,cfs,meta) plots the spin-up and spin-down coefficients of the joint time-frequency scattering (JTFS) transform cfs using the coefficient metadata meta and the JTFS network jtfn. The scattergram function undocks and plots the JTFS coefficients in the current figure. cfs and meta are outputs of scatteringTransform.

Note

By default, scattergram assumes the spin-up and spin-down coefficients are in cfs.

scattergram(___,Name=Value) specifies options using one or more name-value arguments. You can add these arguments to the previous input syntax. For example, to plot the first-order time scattering coefficients filtered with the frequency lowpass filter, set PlotType to "S1FreqLowpass".

Examples

Visualize JTFS Coefficients of Multichannel Chirp

Use the helper function helperEchirp to generate a two-channel chirp with 2048 samples in single precision. The first channel contains an up-chirp, and the second channel contains a down-chirp.

len = 2048;
chirpRising = helperEchirp(10,400,len);
chirpFalling = helperEchirp(400,10,len);
multiChirp = single([chirpRising' chirpFalling']);

Create a JTFS network appropriate for the single-precision signal. Specify a time invariance scale of 32 samples and a quality factor of 16 for the first-order time wavelet filter bank. For the frequency wavelet filter bank, specify 2 octaves and an invariance scale of 2.

jtfn = timeFrequencyScattering(SignalLength=len, ...
    FilterDataType="single", ...
    TimeInvarianceScale=32, ...
    TimeQualityFactor=16, ...
    NumFrequencyOctaves=2, ...
    FrequencyInvarianceScale=2);

Obtain the JTFS transform of the signal.

[cfs,meta] = scatteringTransform(jtfn,multiChirp);

Visualize the spinned coefficients of both channels. The spin-up coefficients preferentially localize the up-chirp in the first channel, while the spin-down coefficients preferentially localize the down-chirp in the second channel. Because the frequency spacing in JTFS is logarithmic, the chirps appear linear.

scattergram(jtfn,cfs,meta,NumChannel=1)

figure
scattergram(jtfn,cfs,meta,NumChannel=2)

Helper Function

helperEchirp — Generate a chirp

function y = helperEchirp(f0,f1,N)
% This function is only intended to support examples in the Wavelet
% Toolbox. It may be changed or removed in a future release.
t = 0:1/1e3:(N*1e-3)-1e-3;
t1 = 2;
phi = 0;
tempVector = (f1/f0).^(t./t1);
instPhi = (t1/log(f1/f0)*f0)*(tempVector-1);
y = cos(2*pi*(instPhi+phi/360));
end

Input Arguments

jtfn — Joint time-frequency scattering network

timeFrequencyScattering object

Joint time-frequency scattering network, specified as a timeFrequencyScattering object.

cfs — Joint time-frequency scattering transform

dictionary object

Joint time-frequency scattering transform, specified as a dictionary object. cfs is the output of scatteringTransform.

meta — Joint time-frequency scattering transform metadata

cell array

Joint time-frequency scattering transform metadata, specified as a cell array of tables. meta is the output of scatteringTransform.

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.

Example: scattergram(jtfn,cfs,meta,NumChannel=2,NumBatch=3) plots the spinned, that is, spin-up and spin-down, coefficients of the second channel in the third batch.

PlotType — Coefficients

"Spinned" (default) | "S1FreqLowpass" | "S1SpinUpFreqLowpass" | ...

Coefficients to plot, specified as one of the following:

• "Spinned" — Second-order time scattering coefficients with spin-up ("SpinUp") and spin-down ("SpinDown") wavelets

• "S1FreqLowpass" — First-order time scattering coefficients filtered with the frequency lowpass filter

• "S1SpinUpFreqLowpass" — First-order time scattering coefficients with the spin-up frequency wavelets

• "SpinUp" — Second-order time scattering coefficients with spin-up wavelets

• "SpinDown" — Second-order time scattering coefficients with spin-down wavelets

• "U2JointLowpass" — Second-order time scattering coefficients filtered with joint lowpass filters

NumChannel — Coefficient channel

1 (default) | integer

Coefficient channel to plot, specified as a positive integer. NumChannel is greater than or equal to 1 and less than or equal to the size of the channel dimension in the coefficients array.

NumBatch — Coefficient batch

1 (default) | integer

Coefficient batch to plot, specified as a positive integer. NumBatch is greater than or equal to 1 and less than or equal to the size of the batch dimension in the coefficients array.

Version History

Introduced in R2024b