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I've read this Wikipedia article on parallel fifths, which also touched on parallel octaves. However, I'm having difficulty understanding the difference between doubled and parallel octaves. I think I understand what a parallel fifth is, and I thought I understood a parallel octave. However, the example of the Washington Post (awesome piece) threw me off. If I have the same melody octaved over itself, is that a parallel or doubled octave? What am I missing?

Are either of these the same as a consecutive octave?

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You might also be helped by these pages: music-theory.ascensionsounds.com/tag/parallel-octaves and tonalityguide.com/tkforbidden3.php –  Ulf Åkerstedt Feb 3 '13 at 21:22

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up vote 10 down vote accepted

The words denote totally different concepts and the difference lies in the arrangemental intent for the instruments playing tones in parallel octaves:

Parallel, or consecutive, octaves
If the intent of an arrangement is to have independent voices but two (or more of) them happen to move in parallel at the octave (or in unison, or two or more octaves apart) at some point, then you are dealing with parallel, also called consecutive, octaves which is considered "bad" in some contexts; it's considered as a mistake in the arrangement. A parallel octave refers only to two consecutive notes!

Octave doubling
If you have two or more instruments that are intentionally arranged to play the same voice (in unison or) one or more octaves apart, then you have octave doubling, which gives you a fat sound. Octave doubling refers to longer passages of music; most likely at least a full phrase in order be meaningful.


More ranting:

Parallel octaves equals consecutive octaves. An example of this, say in a SATB choir arrangement, would be having the bass voice and the alto voice both sing first a G and then a C (or any other two same consecutive notes one (or two) otave(s) apart or in unison). When the intent is to have voice leading with independent voices - where each part plays a role of its own - this is considered bad, especially in music styles of the common practice period, since the parallel voices for a moment loses their independence and start to sound as one unit; e.g. a four part arrangement will momentarily sound like a three part arrangement, and this moment will stick out in an uncomfortable fashion.

The Washington Post example features octave doubling. Here all instruments are intentionally playing the same voice albeit doubled in different octaves. The intent is to achieve a fat timbre by doubling all the instruments.

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You have a couple good questions here.

Parallel Fifths and Parallel Octaves occur primarily in realizing functional harmony; whether it is in a chorale, a fugue, or any number of traditional forms of the European Classical tradition.

They are the result of two voices moving in parallel motion - hence the term "parallel fifth / octave." They are forbidden in counterpoint because they weaken the integrity of the independence of the voices. This is one of the reasons why Debussy's parallelism caused such a stir when he began using it consistently.

The rules change a little bit when a large ensemble comes into play. Composers will double melodies at the unison or octave to provide different timbres - the texture of the sound. To answer your question, if you have a melody doubled over itself at the octave, it is both doubled and in parallel motion, so it's both.

Why is that not wrong?

Because the context of the rules have changed.

Typically with a large ensemble, a composer will maintain the SATB (soprano, alto, tenor, bass "voice") integrity of the overall musical texture. Large ensembles are divided into three, sometimes four choirs: the woodwind choir, the brass choir, the string choir, and the percussion choir. Within each of these choirs composers distribute the voices according to the sound that they want to achieve. To this end, they usually end up "doubling" music that they've already written with several types of instruments.

This is why the trumpets for example can play the same line as the flutes and they're technically not breaking any rules.

"Consecutive octaves" are just another name for "parallel octaves", so no worries there.

It is important to note that I am speaking very generally about this with respect to large ensembles and a specific time period. There are exceptions to every circumstance.

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So, the difference between doubled octaves and parallel octaves is that doubled octaves are the melody being played by two instruments and parallel octaves are the melody and harmony coinciding an octave apart? –  American Luke Feb 3 '13 at 2:37
    
@Luke: If two voices produce notes which are in unison, or differ by a fifth, or an octave, or some number of octaves and a fifth, and the voices both move by the same upward or downward interval, they may be perceived as representing one musical line. It's fine if different parts of a piece have different numbers of musical lines, but the places where the number of lines changes should "make sense". –  supercat Feb 4 '13 at 19:52

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