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Re: Strange FFT AUDIO


From: Jeff Long
Subject: Re: Strange FFT AUDIO
Date: Mon, 19 Apr 2021 14:30:53 -0400

Right, actual signals are not perfect. If they were, you would have no harmonics at all (assuming you are using a sin or cos source). You do not show the dB scale, but it looks like the 1kHz spike is quite a bit larger than anything else.

On Mon, Apr 19, 2021 at 2:13 PM Alberto <alberto_gnuradio@libero.it> wrote:

Hi to all!
I have created a simple test in GNURadio.

Audio Source (audio pc interface) ——> QT GUI FREQUENCY SINK.

Audio is 1 KHz sine wave generate from Hp-8604B from FM bnc output.

In QT FREQUENCY SINK i see this:



Center frequency is 1 KHz.

This are a blocks:




In this image, same signal, but with other audio analysis.


why these huge differences?

Why a second peak at 2 KHz with same amplitude of 1KHz ?

ok it could be a harmonic ... but not of the same amplitude

Bye
Alberto


Inviato da iPhone

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