What determines dissonance?

[wotgoplunk]

Sounds simple enough. (nothing on the search btw, this has probably been asked before).

So to elaborate a bit, why do we classify a minor 2nd as dissonant, yet a perfect 5th as a consonance?

Is it just what is aurally pleasing (no pun intended!) that defines it? I personally really dislike the sound of a perfect 5th, to me, it sounds dissonant, but I have no problem with the majority of modern music.

But here's my catch. Please don't use that complex mathematical stuff. 

Is there an uncomplicated method to define it?

[m1469]

Well, of course I am very interested in this subject, too.  I will just say that I believe that 3rds used to be considered "dissonant."

[thalberg]

Overall the uncomplicated method would be to say that dissonant sounds clash and consonant sounds blend.

Sound subjective? It is.  Different people in different periods defined consonance and dissonance in different ways.  Medieval folks thought fourths were consonant; Enlightenment folks considered them dissonant.   Overall I say do not lose sleep over it.  Though if fifths sound dissonant to you, I find that odd.

[wotgoplunk]

Overall the uncomplicated method would be to say that dissonant sounds clash and consonant sounds blend.

Sound subjective? It is.  Different people in different periods defined consonance and dissonance in different ways.  Medieval folks thought fourths were consonant; Enlightenment folks considered them dissonant.   Overall I say do not lose sleep over it.  Though if fifths sound dissonant to you, I find that odd.

Surely a diminished seventh chord, or even a dominant seventh chord blend, yet have dissonant intervals? If I listen to a V⁷ it sounds pleasing. The tones don't seem to clash.

They're not odd in a chord. After hearing a perfect fifth a few times though, it doesn't sound right to my ear at all. A bit odd, I'll give you that. 

[mcgillcomposer]

Sounds simple enough. (nothing on the search btw, this has probably been asked before).

So to elaborate a bit, why do we classify a minor 2nd as dissonant, yet a perfect 5th as a consonance?

Is it just what is aurally pleasing (no pun intended!) that defines it? I personally really dislike the sound of a perfect 5th, to me, it sounds dissonant, but I have no problem with the majority of modern music.

But here's my catch. Please don't use that complex mathematical stuff. 

Is there an uncomplicated method to define it?

Your question has a simple one word answer: context.

For example, a P5 can be dissonant in a certain context, and consonant in another.

[thalberg]

Your question has a simple one word answer: context.

For example, a P5 can be dissonant in a certain context, and consonant in another.

Just out of curiosity, can you give an example of a context in which a perfect fifth would be dissonant?   

[mcgillcomposer]

Just out of curiosity, can you give an example of a context in which a perfect fifth would be dissonant?   

Sure - consider a passage with triadic harmony...very rich thirds - a nicely flowing counterpoint that builds to a climax on a perfect 5th ... it will sound very dissonant.

[thalberg]

Sure - consider a passage with triadic harmony...very rich thirds - a nicely flowing counterpoint that builds to a climax on a perfect 5th ... it will sound very dissonant.

Interesting!

[wotgoplunk]

Sure - consider a passage with triadic harmony...very rich thirds - a nicely flowing counterpoint that builds to a climax on a perfect 5th ... it will sound very dissonant.

Question then, in an atonal piece chock-full of "dissonant" chords...would a perfect unison then be considered dissonant?

[mcgillcomposer]

Question then, in an atonal piece chock-full of "dissonant" chords...would a perfect unison then be considered dissonant?

It depends on how it is approached - but most likely, ya.

[counterpoint]

Question then, in an atonal piece chock-full of "dissonant" chords...would a perfect unison then be considered dissonant?

I suppose, mcg means a cognitive dissonance (sort of "there's something wrong!?!?"), not a real musical dissonance.

[gyzzzmo]

l

[mcgillcomposer]

I suppose, mcg means a cognitive dissonance (sort of "there's something wrong!?!?"), not a real musical dissonance.

Yes, but that is what counts. It is all about what we perceive.

[stringoverstrung]

Yes, but that is what counts. It is all about what we perceive.

I'm not an expert but if i'm not mistaken there is also a objective side to dissonance, has to do with frequency, harmonics and fourrier analysis if i'm correct.
(like octave is double the frequency so should never be dissonant)

[mcgillcomposer]

I'm not an expert but if i'm not mistaken there is also a objective side to dissonance, has to do with frequency, harmonics and fourrier analysis if i'm correct.
(like octave is double the frequency so should never be dissonant)

Bang on!

[danny elfboy]

Consonance and dissonance depends on the ratio of vibrations.
The octave of a note has twice the vibration of the note so the ratio is simply 2:1
The fourth therefore has a ratio of 4:3
The fifth has a ratio of 3:2

Simple ratio = consonance

A minor second has a ratio of 21:12
A diminished fifth has a ratio of 17:24

Complex ratio = dissonance

The same applies to chords.
Major chords have simpler ratios and are therefore received as simpler information.
Minor chords have more complex ratios and are therefore received as complex information which causes us to perceive them as more intimate, emotional and "sad".

[steve jones]

Sounds simple enough. (nothing on the search btw, this has probably been asked before).

So to elaborate a bit, why do we classify a minor 2nd as dissonant, yet a perfect 5th as a consonance?

Is it just what is aurally pleasing (no pun intended!) that defines it? I personally really dislike the sound of a perfect 5th, to me, it sounds dissonant, but I have no problem with the majority of modern music.

But here's my catch. Please don't use that complex mathematical stuff. 

Is there an uncomplicated method to define it?

Absolutely. The ratio between fundamentals is what determines dissonance. The more complex the ratio, the greater the dissonance.

A good example would be to detune guitar strings of the same pitch. The pulsing that you hear quickly leads into dissonance. But at that point just before, you can create some beautiful 'chorus' effects. The orchestral string section relies on this to achieve that wonderful 'thickening' in tone.

So perhaps it is important to note that ratio complexity defines dissonance only up to a point. Beyond 1/4 tones, it becomes seriously difficult to identify discrete pitches (Im not sure its even possible). Hence the most extreme dissonance becomes unison, the most perfect consonance!

SJ