# I cannot get Spectrogram to highlight a single frequency signal

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John Hunt on 15 Jun 2020
Answered: John Hunt on 16 Jun 2020
I want to use the spectrogram function in matlab, before I do I wanted to make sure I understand it. So I did a small example with a sin wave with 440 Hz as the frequency. However, when I run the spectrogram function its shows that the strongest frequency is around 70 Hz. I would love some clarification.
x = 1:.001:5;
y = sin(440*x);
figure(1); plot(x,y)
figure(2); spectrogram(y, 1000, 500, [], 1000, 'yaxis');
Thanks
##### 2 CommentsShowHide 1 older comment
John Hunt on 16 Jun 2020
Well, that would make the difference. Thank you for pointing that out to me.

John Hunt on 16 Jun 2020
dpb answered this question in the comments sin() uses radians and the conversion from radians to hertz is 1/(2pi) and 440/(2pi) is 70.03.

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