Matlab 2023a: How can I set Window Length and NFFT in the Spectrum Analyser block in Simulink?

The spectrum setting for the Spectrum Analyser in Simulink Matlab 2023a don't appear to allow direct adjustment of the Window Length and NFFT. They could easily be set in previous versions. Is there a way to change these settings?

Answer 1

[Vandit]

Hi Donal,

I understand that you are facing difficulty in changing the 'Window Length' and 'NFFT' in the Spectrum Analyzer block in MATLAB R2023a.

From the below documentation, it looks like there is a change in the GUI of the Spectrum Analyzer block:

https://www.mathworks.com/help/dsp/ref/spectrumanalyzerblock.html#mw_b98e44df-ff40-45eb-a01f-b5c5f1297b51:~:text=R2023a%3A%20Spectrum%20Analyzer%20with%20improved%20responsiveness%20and%20toolstrip%20interface%20in%20Simulink

One workaround is to use the "set_param" and "get_param" functions, which are used to modify and retrieve block parameters in Simulink, respectively. Kindly refer to the following code snippet for modifying the 'Window Length' and 'NFFT' in the Spectrum Analyzer block:

% Get the current block path
>> gcb

ans =

    'untitled/Spectrum Analyzer'
    
% Get the current Window Length
>> get_param(gcb,'WindowLength')

ans =

    '1000'

% Set the Window Length to 1024 and verify the Window Length has been updated   
>> set_param(gcb,'WindowLength','1024')
>> get_param(gcb,'WindowLength')

ans =

    '1024'

% Get the current FFT Length (NFFT)    
>> get_param(gcb,'FFTLength')

ans =

    '256'

% Set the FFT Length to 1024 and verify the FFT Length has been updated     
>> set_param(gcb,'FFTLength','1024')
>> get_param(gcb,'FFTLength')

ans =

    '1024'

To know more about "set_param" and "get_param" functions, please refer to below documentations:

Set Simulink parameter value - MATLAB set_param (mathworks.com)

Get parameter names and values - MATLAB get_param (mathworks.com)

Hope this helps.

[Donal O'Toole]

Hi Vandit,

Thank you very much. The gcb, set_param and get_param commands go a long way to solving the issue. set_param(gcb,'FFTLength','1024') works perfectly on Matlab R2022b but get_param(gcb,'WindowLength') does not:

>> get_param(gcb,'WindowLength')

Scope block does not have a parameter named 'WindowLength'

The Window length parameter is clearly visible when I open the block in question so it's a bit surprising.

I've yet to try these commands on the Matlab R2023a version. I'll report back after I do.

Thanks again,

Donal