How to change key? I understand I open the pop-up menu above and just choosing a new key and before I shut down (leave) the project I just save my changings and so i have gotten a new key of the song, right? It's that simple.. ? It seems like in me it works. But in internet I read that I need to choose timeline, then hit command x, then have to choose the right key and then command p. This last sentence is not relevant, if I can choose a new key and save changes and thus also a new key is gotten.. ?

The first part of what you said is correct, but keep in mind that if you change the Key up top after you've recorded a bunch of tracks, the Software Instrument tracks will be transposed automatically but the audio tracks will not be transposed automatically, you'd have to manually match the new key with the Transposition slider (or better, with the Vocal Transformer). It's a bit complicated, and clunky, so unless you specifically need to change the key of a song after you've already recorded some tracks there's really no reason to mess around with the Key. Video #8 in the course attached above shows the use of the Key popup menu at the top. I don't know anything about command x and p and the timeline..?

But there is a need to change the key always. I mean, I have recorded some part of the song (without my voice) and as I don't know in which key the song sounds better, I need to try all of the keys... Having sense.. ? If you will make a new song, how do you know, which key is netter for you.. ? Or do you have the favourite keys already? I haven't made any song yet and I am not in common about the keys, thus is a good idea to change them and listen to, which sounds best to my project. If i have found a right ley, only after it I use the vocal, thus transposing the software instrument tracks is not a problem, as it does automatically anyway. I also enclose a video where is the command x choice is seen... Maybe it has a sense as there also vocal (audio track) is involved.. ? I mean, with command x I can change audio file easily.. ? I myself have never done it. https://youtu.be/rk5VAwtNjk8

Ok, that workflow sounds fine -- as long as you record the vocal after you've determined the best key for you, you avoid having to transpose the voice, which does not sound as good as transposing the Software Instrument tracks, which works fine. As I said, if you have a reason to transpose -- in your case to find the best key to sing in -- then it makes sense for you to use that feature as you do. Remember, I have no idea what your workflow is, so I can't really make suggestions on how you should approach things -- I can only comment on how certain features in GB work, not whether or not you should use those features. Regarding the video.. I have no idea what he's trying to do there -- the video starts in the middle, I can't hear him, and the tiny snippet of music sounds the same before and after he does whatever he does, so it doesn't really make any sense to me..

You write that audio track will not be transposed automatically in case of changing the keys. Well, I recorded vocal in c maj and then changed key to e min and my vocal sounds very differently. What is that, if not transposition of vocal to the other key.. ?? But it sounds very strange, that e min. Is that normal e min or unnormal e min? In last case, anything is wrong.. ? Video is enclosed. https://youtu.be/lGWxjx_Rw90

Hmm.. I tried it again and it did work for me -- apparently the Enable Flex button in the Editor pane > Track tab has to be off for that track for key changes to be automatically applied to Audio tracks as well as to Software Instrument tracks -- last time I tried it I had that button on, which seems to prevent Audio tacks from following key changes made up top. Strange limitation -- I can't imagine why that should be, other that it must be just another limitation in the time and pitch shifting capabilities of GarageBand [which is, after all, free, and so deliberately limited in what it can do]. And yes, when you change the key on an Audio track -- especially a vocal track -- it's likely to sound strange, that's a limitation of pitch-shifting in general and especially the pitch-shifting quality in GarageBand. It's not a particular key that makes it sound strange, but how far away from the original key you change it -- so, for example changing the key from C to D [2 semitones away] may sound ok, but changing it from C to G [7 semitones away] is likely to sound strange and unnatural.

So you say that from C to G sound is strange and unnatural. OK. There are 2 ways to improve it - change step by step from key to key C to D, D to E etc until G. So we are changing always close keys and the result will be OK then, right.. ? Or after I have changed key right from C to G, I use vocal transformer and its Formant to get the voice more natural... Right? That's only a theory, I must to try it, too.

No, changing pitch incrementally like that will not make larger transpositions sound better, because you're not actually changing it gradually -- every time you choose a transposition value it's recalculating it from the original pitch. AFAICT the best way to get better transposition quality in GB is to use just the Vocal Transformer to transpose, instead of any other method of transposition. If you transpose all tracks including the vocal with the Key menu at the top, you'll usually get poor sound quality on the vocal -- you could try to improve that by opening a Vocal Transformer plug-in on the vocal track, leaving its Pitch slider at 0 [since the vocal has already been transposed by the Key change], and setting to Formant slider to compensate. So, for example, if a Key change from C to G makes the voice go DOWN in pitch, then you'd set the Formant slider in the Vocal Transformer UP by an equal number of steps. C to G is 7 semitones if the pitch goes up, and 5 semitones if the pitch goes down -- when I tried that Key change it made the voice go DOWN to a lower G [5 semitones lower], so setting the Vocal Transformer Formant slider UP to +5 compensated, for a better sounding vocal transposition, similar to what I got if I just used the Vocal Transformer and not the Key change menu. This seems to work, but you have to know the number of semitones that a Key change is moving the pitch up or down to be able to effectively compensate with the Vocal Transformer's Formant slider, so it requires an understanding of the relevant music theory -- the number of semitones between one key and another, going either up or down in pitch. Alternatively, you could transpose all Software Instrument track Regions with the Transpose slider in the Editor pane, but transpose Audio (vocal) tracks only with the Vocal Transformer. Then you could just set the Transposition values in both places numerically to the same number, which might be easier -- a little more work if you have a lot of tracks, but it doesn't require as much music theory knowledge about keys and semitones..

OK. But much more easy is to record some regions in (2x) 7 different tracks ( all in different keys, the voice and piano for example ), thus I get 7 original keys and then to compare, which of them is sounding better... Right.. ? I am just now realizing that.. (smile)

I guess you could do that, record multiple takes of your voice in different keys and then go back and listen to those multiple takes of your singing in different keys to determine which key you like best for your voice -- if that workflow works for you then you might as well go with it.. Some people might just record a Software Instrument track, sing along with it live at different keys until they find a key that's comfortable, and then record the vocal. But if you need to hear your voice in playback to get a better idea of which key you like it best in, then your approach seems fine..