How to display data saved with getSpectrumData? Why are saved values different from input?

Hello dear community,

in my example code I create two sinus signals, display it with spectrumAnalyzer and save data to tables (later I will use it to receive data from hardware device). There are 3 ways to display it: 1. time I just display a created sinus-signal

and save it directly to variable "y" directly and to variable "data" using getSpectrumData function.

When I display "y" it works perfectly:

when I try to display "data" saved by getSpectrumData I get no signal information:

What is wrong?

Thank you!

% create two sinus signals
wave = dsp.SineWave(Frequency=100,SampleRate=1000);
wave.SamplesPerFrame = 1000;
wave2 = dsp.SineWave(Frequency=150,SampleRate=1000);
wave2.SamplesPerFrame = 1000;

% init variables
data = [];
y = [];
frames = 500;

% init scope 1
scope = spectrumAnalyzer(SampleRate=wave.SampleRate,...
ViewType="spectrum-and-spectrogram",...
FrequencyScale="Linear");

for ii = 1:frames
    x = wave() + 0.5*wave2()+ 0.05*randn(1000,1);
    scope(x); % spectrum of created signal x
    if scope.isNewDataReady
        y = [y,x]; %save input signal
        data = [data;getSpectrumData(scope)]; % save signal using getSpectrumData
    end
end
release(scope)

% init scope 2
scope = spectrumAnalyzer(SampleRate=wave.SampleRate,...
ViewType="spectrum-and-spectrogram",...
FrequencyScale="Linear");

for a = 1:width(y)
    scope(y(:,a)) % spectrum of saved signal y
    pause(0.01)
end
release(scope)

% init scope 3
scope = spectrumAnalyzer(SampleRate=wave.SampleRate,...
ViewType="spectrum-and-spectrogram",...
FrequencyScale="Linear");

for a = 1:height(data)
    scope(data.Spectrum{a,1}) % spectrum of saved signal using getSpectrumData
    pause(0.01)
end

[Nik Rocky]

No ideas? =(

[Khodour Al Kadry]

Hi Nick

getSpectrumData will return the computed spectrum in frequency domain. In your third case where you are plotting the saved data using getSpectrumData, you are actually plotting the frequency response of data that is already in frequency domain.What you should do, is set the InputDomain='frequency' on spectrumAnalyzer, this will allow you to plot pre-computed spectrum (frequency doamin data).

Regards

-Khodour