# How can I understand FFT about MATLAB

## Forum: Digital Signal Processing / DSP / Machine Learning FFT amplitude at different frequencies-Matlab

Hello everyone, I have an audio signal with a tone that was generated with a sine tone generator, the frequency of which I want to determine. In addition, there is interference on the audio signal in the form of a person speaking, but the sound is played continuously. Before I analyze my audio signal with an FFT, I put a window function over it to smooth the ends and avoid jumps. The FFT gives me the frequency. But I don't understand why the amount of the FFT is highest at this frequency, even though a person speaks repeatedly in this audio signal. The amount depends on the fact that the tone was played continuously or on the volume, because the person speaking is temporarily louder than the sound. I just want to understand, because for me all of this has the advantage that I can quickly find my frequency by filtering for the highest amount.

: Postponed by the moderator

Moin, look at this: https://www.gomatlab.de/einheit-der-amplitude-im-frequenzspektrum-t29162.html and just play around with MATLAB a little. Generate a few sine waves and do an FFT of them. Vary the frequency and amplitude of the signals, mix signals and see what comes out.

Mm N. wrote:> But I do not understand why the amount of the FFT is the highest at this> frequency, although> a person speaks over and over in this audio signal with the volume,> because the person speaking is now louder> than the sound. Not "or", but "and" :) Just imagine that using the energy (= integral of power over time): The tone has a fairly constant frequency all the time, so the entire energy adds up in one (sharp == very narrow) spectral line. The speech signal has a considerable spectral width; As you can see in the spectrum, its energy is distributed over many spectral lines, which is why the individual line cannot get so high. Even so, the speech signal could have a higher total energy than the sound; you would have to do the math.

### Important rules - read first, then post!

• Use upper and lower case
• Do not insert longer source code in the text, but as a file attachment

• [c] C code [/ c]
• [code] code in other languages, ASCII drawings [/ code]
• [math] Formula in LaTeX syntax [/ math]
• [[Title]] - Link to article
• Insert reference to another post: right-click on the post title,
"Copy address" and paste it into the text