The problem with the above explanation is that it starts at a lower level of abstraction than is warranted. Analogously, it explains MOSFET's rather than algorithms. The fundamental unit of Music Theory is the Interval (as in "frequency interval between notes"). A better explanation would have explained Intervals, how particular combinations of Intervals form various Scales, and how Scales influence Chord Progressions and Key Signatures.
There are 12 unique notes in an Octave (yes, octave means 8; ignore this for now). On the 13th note, the octave repeats itself (counting is 1-indexed). But of these 12 notes, only specific subsets are combined into specific scales.
The most popular scale is the Major Scale which follows the pattern "Tonic Major_2nd Major_3rd Perfect_4th Perfect_5th Major_6th Major_7th" (there exist other notations). The Major Scale imparts a generically-happy mood. But there's other scales, including: the Chromatic Scale; the Major Scale; 3 varieties of Minor Scales; 7 varieties of Diatonic Modes (including Major and Natural Minor); the Pentatonic Scales; etc. E.g. Smoke on the Water, Sunshine of your Love, and Fight for your Right (to Party) all sound similar because they use the Blues Scale.
Once you familiarize yourself with the intervals, scales, and their various notations (which is its own feat), you can jump into the meat & potatoes of Music Theory. Which mostly consists of analyzing Chord Progressions and Key Signatures in order to find commonalities in mood. Chord Progressions and Key Signatures determine a song's general mood. It's too complicated for me to summarize quickly. But it's where all the interesting stuff happens.
N.B. I've deliberately omitted various details for the sake of brevity. E.g. I could have mentioned Time Signatures, Rhythms, Tempo, Dynamics, etc.
> The fundamental unit of Music Theory is the Interval (as in "frequency interval between notes"). A better explanation would have explained Intervals, how particular combinations of Intervals form
Guess what... A perfect fifth is a 3:2 ratio/interval of frequencies (+/- a small allowance for the historical/mechanical constraints that lead to well/equal tempering unless we're talking modern micro-tonalism in which case no adjustments are necessary). The inverse, 2:3, is a perfect fourth.
The example frequencies I gave correspond to concert-A, then E and D. I took a very simple/short path from intervals to harmonic function/progression to try to give a taste of the meat and potatoes before providing a link to additional sources.
I avoided music theory terms because that would've been a circular definition for any readers who had no understanding of even the basics.
In light of your post, I should've added a sentence or two about mood (major = happy, diminished = tense/scary) and compared that to how you can make a 'warm' picture using reds, oranges and yellows or a sombre picture with darker colors, etc.
I didn't learn music through Youtube. So unfortunately, I'm not familiar with any videos that I would consider comprehensive or canonical. At best, I can share videos that highlight a particular pattern, or share examples of popular songs that I recognize as having a commonality. Which might give you a better feel for what music theory is.
Another thing to keep in mind is that musical patterns accrete into genres. And there's a wide variety of genres. So it's difficult for any single video to cover everything in detail. I think it's more common for videos to cover the patterns of a particular genre. E.g. if you're interested in Blues, consider searching for videos about Blues.
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https://www.youtube.com/watch?v=xm4LO22-cyY
I remember the above Vox video highlights a unique chord which sounds "melty" and is often used in holiday music. The chord is known as a "minor_7th, diminished_5th" aka "m7d5".
https://www.youtube.com/watch?v=5pidokakU4I
This video is about the infamous "4-chord pop progression". It's ubiquitous on the radio. Elitists and connoisseurs tend to look down on it for appealing to casuals. The progression is "I V vi IV" (capital denotes major chords, lowercase denotes minor chords).
https://www.youtube.com/watch?v=kfjXp4KTTY8
When I think of the "12-Bar Blues (Chord Progression)", I think of Stevie Ray Vaughn's "Pride and Joy". But there's tons of educational videos on this. It's very popular in not only Blues, but Rock & Roll. It's "I I I I; IV IV I I; V IV I I". But things get interesting here because musicians often substitue "jazzy" chords like Dominant_7th's (aka V^7). For bonus points, look up "tritone" (N.B. Rock is truly the devil's music).
https://www.youtube.com/watch?v=dISEg1ydQoM
I'm not actually sure what song I'm thinking of, but there's a particular trope often used in Hollywood films to denote a bullfight. It's based off the Phrygian Mode, which tends to sound very "spanish-y". In lieu, I've linked the the first bullfight track I found.
https://www.youtube.com/watch?v=X4fa44_sq2E
A genre I'm particularly fond of is House. Which is often characterized by its "Four on the Floor" drum beat. It's very simple, just continuous quarternotes of kicks. The rhythm is sometimes denoted "1 2 3 4" (where the structure of a single bar is "1 e & a 2 e & a 3 e & a 4 e & a"). The above video is Daft Punk's "Superheros".
And then there's Jazz. Which is hard to explain, because it's the genre where anything goes. And besides jazz, there's lots of other techniques and obscure genres that I can't possibly cover in a single post.
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In any case, I'd suggest looking up a particular genre you like and studying it. If you're a musician, learn scales. 90% of pop music these days uses either Major or Natural Minor. But you can really expand your horizons by learning other scales. It's boring, but it builds a strong foundation. Like how a basketball player will run laps rather than shoot freethrows all day.
There are 12 unique notes in an Octave (yes, octave means 8; ignore this for now). On the 13th note, the octave repeats itself (counting is 1-indexed). But of these 12 notes, only specific subsets are combined into specific scales.
The most popular scale is the Major Scale which follows the pattern "Tonic Major_2nd Major_3rd Perfect_4th Perfect_5th Major_6th Major_7th" (there exist other notations). The Major Scale imparts a generically-happy mood. But there's other scales, including: the Chromatic Scale; the Major Scale; 3 varieties of Minor Scales; 7 varieties of Diatonic Modes (including Major and Natural Minor); the Pentatonic Scales; etc. E.g. Smoke on the Water, Sunshine of your Love, and Fight for your Right (to Party) all sound similar because they use the Blues Scale.
Once you familiarize yourself with the intervals, scales, and their various notations (which is its own feat), you can jump into the meat & potatoes of Music Theory. Which mostly consists of analyzing Chord Progressions and Key Signatures in order to find commonalities in mood. Chord Progressions and Key Signatures determine a song's general mood. It's too complicated for me to summarize quickly. But it's where all the interesting stuff happens.
N.B. I've deliberately omitted various details for the sake of brevity. E.g. I could have mentioned Time Signatures, Rhythms, Tempo, Dynamics, etc.