why do certain chords in music sound “better” than others?

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So I don’t know a ton about music theory, but I’m curious about how this works. Why do our brains like to hear chords that are in tune? And how do we explain why something is tuned properly?

In: 32

It is difficult to say “why” we associate certain combinations of sounds with specific emotions – there are some theories that we have developed to get alerted by specific non-harmonious sounds, that may indicate the presence of predators, while other sounds – like birdsong – indicate no danger. Or at least we had an advantage in interpreting warning and/or “all clear”-sounds from other species… But to me this all sounds rather far-fetched.

Fact is, some of these combinations (like the perfect fourth or fifth) are perceived as harmonic, others (like the tritone) don’t immediately harmonize.

However, I would not agree that “some chords” don’t sound good: a crafty musician can make any chord sound “good”, by just putting it into the right context. This is admittedly easier for some chords than for others … or maybe it is just that most of us just have more experience with how to use, e.g. Am than something as harmonically complex as e.g. F#13b9.

Music and chords can be thought of as combinations of sounds. And sounds are simply vibrating air molecules. The speed at which they vibrate determines the pitch (high or low) that we experience, and we measure that as frequency (in units of Hertz or Hz), or how many times it vibrates in 1 second.

As the frequency increases, so does the pitch, but this relationship is not linear. In fact, when we double the frequency, we will hear the same “note” but one octave higher. E.g. 440Hz is an A, and 880Hz is the next higher A, and 1760Hz would be another A. Since they are doubles of the same frequency, the wavelengths of the notes will easily match up and therefore sync together. The same can be said of other multiples of the base frequency, 440×3, 440×5, 440×6 etc. which is why when you hear these notes together, they sound in tune. The oscillations would line up fairly often.

On the other hand, frequencies that are “out of tune” are often the most noticeable, because their frequency is ever so slightly higher or lower than the multiple they’re supposed to match up to, so the wavelength oscillations never quite line up happily.

As we try to tune to increasingly complex intervals (distances between the notes), it becomes harder to tell, however tuning by an octave is usually the easiest, as it is simply double or half the frequency. With practice, we are able to identify different intervals with ease.

Chords can be dark or bright with many colours in between. A basic triad or 3 note chord consists of the I, III, and V notes of the scale with the same root as the chord. Major triads are happy, and some keys are more happy; a major C is ‘bouncy’, a major F is more ‘romantic’. Minor triads are dark or ‘sad’, it’s just a major triad with a flat III note. Among minor chords some sound more sad, such as A minor and D minor.

Adding a VII (7th note, or I-III-V-VII) adds another level of colour; a natural VII gives you a dreamy major 7th chord. A flat VII note makes you want it to resolve to the major I chord (when it’s a V7 ‘dominant’ chord). That’s the basics but there are other colours that can be added like a flat 5th or flat/sharp 9th, 11ths and 13ths as well, a suspended 4th, the 6th instead of the 5th, and so on, depending on what the melody is doing. Essentially what is happening is, tensions are created, then they are resolved, harmonically speaking.

There are sonorous and dissonant intervals. Our culture informs us just how much dissonance sounds “good”. For example, medieval church singing only used “perfect” intervals of 1:1, 1:2, 2:3, and 3:4 — what are called unison, octave, 5th, and 4th.

Bulgarian folk music uses intervals like flatted 2nd and major 7th that are rarely heard in western choral music.

We are told what sounds good in part by our ears and in part by our expectations.

I think its a combination of maths and culture.

The maths bit is how the frequency spectrum is split up, and how the frequencies of notes relate to each other. In Western music the note A4 is tuned to 440Hz. If we double that to 880Hz we get an A5 ( the same note an octave higher; if we half it we get an A3, so an octave lower. Notes which have a simple mathematical relationship (so 2:1, 3:2 for instance) to each other tend to sound good played together.

The culture bit comes in when you consider that modern music theory is largely based on western classical music. Other cultures/traditions may split the frequency spectrum up differently (Indian classical music, or Indonesian gamelan for instance) and can sound dissonant to ears brought up on different music traditions.