If I look at the picture, you call that curve as an audio (below). I thought it is a frequency curve? Because according to the picture, you are pointing to the place where is seen nothing - no curve I mean, only orange colour, but that is not a frequency, it is a shaded area of band 2. So if only shaded are is seen, how can you say you see a boost and cut of all frequencies? Are they invisible? As only by eye shaded area is seen. If the audio (a frequency?) is one place and bands 2 and 7 only boost and cut above or below the chosen frequency, then of course I will nit hear anything, as they don't touch the chosen frequency (where the audio is). So what sense have the 2 and 7 bands? How can I apply the eq to a signal that has lower notes to hear the effect of 2 and 7? Do band 2 effects only to a lower notes?

No, that's not correct -- the [orange] shaded area DOES represent a range of frequencies, and that's the range of frequencies that will be affected by that EQ band IF there's audio there in that range. When you boost or cut with an EQ you're not just boosting or cutting audio at the chosen frequency, you're boosting or cutting audio at the frequencies around that chosen frequency as well [or in the case of a shelving EQ, al the frequencies above or below the chosen frequency]. The chosen frequency is just the center of the range of frequencies that will be affected by that band, all the frequencies in the range of frequencies [like the orange area I highlighted in the previous screenshot] for that band are affected. But if there's no audio in the signal within that range then the EQ boost or cut won't have any audible effect -- the EQ will be set to boost or cut that frequency range, but if there's no audio there then you've simple selected the wrong range to apply EQ. And that's the problem here -- you were boosting/cutting low frequencies on an audio signal that has no low frequencies. If you want to experiment with low frequency EQ, you'll have to apply it to a signal that actually contains low frequencies. The electric piano sound you were using was playing higher-pitched notes that only contained frequencies above the range of the EQ band you were applying to it [as I indicated with the yellow box in the screenshot]. If you want to try out a low-frequency shelving band on that signal then play lower notes on the electric piano, so the spectral display [the area I drew the yellow box around] shows that there's audio down in the same range as the range of the EQ band you're applying to it.

I played one lower note on the piano, but you see, the sound ends before the note ends. Why is that? Mustn't the sound be during all the length of the note (on a region)? I wanted a long note, thus good to listen band 2. Do you listen to the difference of eq? I don't. You yourself write that has to be an audio in the signal. Well, low notes an audio (do you call sound as audio, as electric piano is midi track and audio track is a different one) but as band 2 doesn't touch the curve (as parametric does), of course, no effect. But you tell shelving eq boosts and cuts everything above or below chosen frequency. As you see by naked I there's nothing to boost or cut (only shaded area on the empty space), thus no effect on the sound is heard. Sense? Sense. I may put as low notes on the piano, but as band 2 doesn't reach to touch the curve - nothing will be changed... I'll send this letter now and video on next post.

The video https://youtu.be/XG5qOtmJxxw

No, the sound [the audible note] does not necessarily have to last as long as the MIDI note length. A MIDI note is only a piece of data, telling the Software Instrument plug-in to sound a particular note -- if that particular instrument plays shorter notes that die out on their own, then the notes may not last last as long as the MIDI note length. If you re-read the previous post you'll see that I said that instruments like piano, bass, or guitar play notes that die away on their own, and it you want an instrument that plays longer notes that will last as long as the MIDI note length you'd have to use a sustaining instrument like an organ or a string sound -- here you've once again chosen a piano that plays shorter notes that die away on their own. If you want longer, sustaining notes you'll have to use a different instrument. And once again you've chosen a sound that has little or no energy down in the range where you're applying EQ, so of course there's little or no audible effect from the EQ. If you look at the screenshot a couple of posts back you'll see where I drew a yellow box around the spectrum display that shows the frequency range of the audio of a note -- if those bumps are above the frequency range of the EQ band you're using [the orange box in that same screenshot], then the EQ can't have any audible effect on the sound. To hear an effect from that low-frequency EQ band you'll have to play lower notes.

So band 2 is for lower notes and band 7 is for higher notes and bands 3-6 are for so called normal, (commonly used on songs) mid range notes? Right?

A low-frequency shelving band is for sounds than include low-frequencies [which would be lower notes], and a high-frequency shelving band is for sounds that include high-frequencies. Btw, most instrument notes include harmonics & overtones that extend to higher frequencies, but not all -- for example, that electric piano doesn't have really have much in the way of higher-frequency harmonics & overtones.

I see your picture where band 2 is and where central frequency is and have remembered your suggestion to choose lower notes, but you can see (the low note is so low it is nearly on the bottom of the region, last long one) and hear the note is very low and it is still not where band 2 is. The low note is not so low to be a real corner frequency. I think the note is so low it is not in use in music at all. So band 2 has normally no use, as not so low notes are in use for it? Or where is a problem? If I choose more lower note as you suggest, it will be out of the region limits, or how... ? Video is enclosed, last part of it is I was talking about. https://youtu.be/VkEzi_J1SE8

All the notes you played were still above the frequency range you were cutting with the EQ, as shown by the spectrum analyzer. To hear the effect of that EQ band [of any EQ band] the frequency range of the note[s] must be within the range of frequencies being affected by that EQ band. To hear the effect of that shelving EQ band you'll have to either play lower notes or maybe try a different instrument, like a bass instrument, and play lower notes on that, so the spectrum analyzer [the yellow box in the screenshot] shows that the notes' frequency range falls within the frequency range of the EQ band in use. Try loading a bass instrument [like Fingerstyle Bass], and if you're penciling in notes, scroll down in the Piano Roll Editor and add notes between C1 and C2 [as shown on the keyboard at the left].

OK, I got it. So the bands 2 - 7 are boosting and cutting. The bands 1 and 8, what means they are moving everything.. ? What everything there still can be besides the audio frequency.. ?