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4.3.6 How Music Affects the Brain: Tune Recognition
Music (tune recognition) arises when your brain compares frequency ratios of a succession of notes, an order of intervals. For music to affect the brain, your brain needs context. If it’s a tune without chords, the first note you hear supplies the beginning of context. The second note provides more information. The third, still more information. And so on.
All the while, your brain is comparing frequency ratios. If it perceives several different simple frequency ratios (for example, 2:1, 3:2, 4:3, etc.) among the note relationships (i.e., the intervals), it figures out there’s an organizing principle at work that is giving rise to the succession of simple frequency ratios it’s perceiving.
What is this organizing principle?
A scale of some sort.
It then expects to hear more notes from the same scale, but not necessarily in the same order.
In fact, your brain will get bored and lose interest in recognizing the tune unless it perceivessome surprises in the relationships between the pitches (the intervals) as the tune moves on.
As soon as the tune begins (sets the musical road trip in motion), your brain goes to work figuring out which note is the tonic—the tonal centre. All of the frequency ratios that define the other intervals depend on the tonal centre for context. The tonic note acts as a kind of gravitational force on the tune as a whole, which is why it’s called the tonal centre.
Your brain perceives a hierarchy of stability, with scale degree 1 (the tonic note) perceived as most stable.