ranjit The first YouTuber doesn't provide good advice imo
The only thing that didn't gel with me with is the same theory topic of intervals. In that vid, he says 'a fifth above' --- the word 'above' will confuse a heap of people I reckon, and it isn't 'coherent' when he teaches it in that way.
LINK - 1053 seconds
Intervals in my opinion - from a particular 'perspective' - involves spans of notes - when words such as thirds, fifths etc are used for teaching that is.
So if the root note is C (in a major scale), then a 'fifth' spans five notes in the key of C. So a fifth (in interval terms), with C as the reference lower note - would involve C and G, with C and G spanning five notes in the key of C (C major). We wouldn't say (like he does) that 'G' is a 'fifth ABOVE C' - in the key of C that is.
When talking about intervals - I reckon that the span of notes makes a heap more sense - from the span perspective that is.
The only condition where saying 'above' makes any sense is when the intervals are in terms of 'distance' between notes - but this only works when the units for example are in number of semitones. That is - G is seven semitones above C, which does relate to an interval of a 'fifth'. But here, tying the number '7' (for seven semitones) to the number '5' becomes a waste of time. Which also means that music theory sites telling students that intervals are distance between notes is somewhat misleading unless they tell people that the 'distance' is in a particular units -- of semitones, but thinking in terms of 'distance' when when dealing with thirds, fifths is a waste of effort -- as it is much more effective to deal with 'span' when terms such as thirds, seconds, perfect fifths etc are used.