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T Chap
Posts: **4,051**

I have a 100hz sine wave that I am adding harmonics to with a tube/saturation plugin. I want to experiment with how different the harmonics look vs the fundamental to see what the simulation is doing to add/create harmonics that weren't there. I haven't tried to look at the output on a scope as it makes sense the scope can only show all voltages combined so it would not be possible to analyze a specific harmonic to see its shape compared to the original. For example how different will a 2nd harmonic (octave) look.

The first obvious though is to try to get a tight filter on the 2nd harmonic and try to view it on a real scope. Then test various waves ie sine saw square triangle. Maybe someone knows a better more accurate way to isolate a frequency and view its shape. The spectrum analyzer only allows so much. Even a square wave looks look a sine. The second image is an example of how what I want to see isolated on a scope.

The first obvious though is to try to get a tight filter on the 2nd harmonic and try to view it on a real scope. Then test various waves ie sine saw square triangle. Maybe someone knows a better more accurate way to isolate a frequency and view its shape. The spectrum analyzer only allows so much. Even a square wave looks look a sine. The second image is an example of how what I want to see isolated on a scope.

## Comments

3,4304,0516,545Also, try an x-y lissajous display of 100Hz against a harmonic.

By the same token, take the 100Hz signal after the saturation plugin, and play it against a second sine wave generator that is locked to a harmonic of 100Hz. At some amplitude and phase, the second signal will cancel out the harmonic component in the distorted signal.

3,430There are basically two ways to visualize a signal. Time domain represents voltage changing over time, which is where you see the actual sine waves if a signal is pure enough and a mishmash if it has a lot of component frequencies. Frequency domain is a graph of the frequencies comprising the signal, such as you get from a spectrum analyzer. In the real world neither graph represents a signal perfectly because of measurement resolution.

You can reconstruct a signal by taking the frequency domain graph and connecting up a bunch of oscillators set to the component frequencies and amplitudes and adding them up, and you could "take out" a frequency by not hooking up that oscillator. In fact this is exactly what you are doing when you play back a MP3 music file, which represents sound as the sum of all the frequencies it contains during each short time slice. But you cannot take out a single pure exact frequency, because each element of the frequency domain graph represents a small range of frequencies. You would need infinitely fine voltage and time resolution to isolate a single pure tone.

In practice as long as we have good but not necessarily perfect resolution we cannot tell the difference between an original sound and a reconstructed sound made of pure tones representing the center frequencies of the elements of the frequency domain graph, which is why MP3 compression works.

19,838Edit: Oh. Harmonics. Never mind.

4,0514,051155https://en.m.wikipedia.org/wiki/Square_wave

https://cnx.org/contents/cvkPOvcs@1/Fourier-Series-Square-wave

3,430Where I think you are misunderstanding this is that harmonics aren't "added" except in very theoretical situations; the waveform is created by some process like toggling a switch or overdriving the vacuum tube, which causes the voltage to change, and harmonics are just

there. Fourier's theorem doesn't say you must add sine waves to create a signal, although it says youcando that; the true significance is thatany signalcan be described as a sum of sine waves, and Fourier analysis just reveals which sine waves you would need to add together if you wanted to replicate the signal that way (which is, incidentally, exactly how mp3 music compression works). All this can be used to design filters and other circuits that affect a signal byhaving the same effectas enhancing or removing ranges of those sine waves. It doesn't mean that at any point all those component sine waves are actually broken out as individual signals that can be inspected separately.4,051