Hi everyone,

I'm trying to understand the concept of relative/parallel scales.

First of all, would I be right in saying that relative scales is e.g. C Major and A Minor (6 steps apart) Say the riff was played in the key of C Major. Then one could play a solo in A Minor and the two together would sound well.

Parallel is when one e.g. plays a riff in C Major and solos in C Minor (or vice versa, I imagine). I imagine this is correct.

So, e.g. when one is playing a riff in a half-whole diminished scale, what would be the relative or parallel scales for that, if any? Are relative/parallel scales only used with modes?

Thanks!

Relative and parallel are two different concepts.

Relative is diatonic - meaning staying within the confines of the major scale.

Parallel has no regard to the staying within the confines of the corresponding diatonic harmony.

So your first example is soloing Am over Cmaj... diatonic (Am is Cmaj's relative minor)

Soloing Cm over Cmaj is exactly what you said parallel.

Now you can only find parallel harmony to a key not particularly to a scale, so it's undetermined how to define half-whole diminished without knowing what key it's based out of.

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Thanks for the reply.

So the concepts of relative/parallel modes can also apply to the diminished scales? I thought they didn't. Could you give me an example, say in the key of C? Thanks!

The Locrian mode is diminished. So if you had something like B Locrian, then that would be in the key of C, so Cm would be the parallel scale.

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Shit... I never realized the Locrian mode was the Diminished scale!

So, davie_gravy, C Minor is the parallel scale to the Locrian mode? Does that mean that the two can be played together (one riff and one solo and vice versa)?

Thanks a lot for the help. I really needed to know this info.

Cm is the parallel to C major. Now, C major contains a diminished mode which would be B Locrian. Cm is not parallel to the Locrian mode, it's parallel to B Locrian. You can only find parallels to keys, not necessary a scale, but I would assume the Locrian mode of Cm (assuming this minor is Aeolian then, it's the key of E), which is D# would prob be the associated parallel mode to B Locrian, both of which were derived from their key.

I don't play using much parallel harmony, I'm more of a diatonic fan, so I can't really vouch over how well particular modes will work with other modes in various keys. You just gotta mess around with em because somehow you can always find an application for it.

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It isn't. (apologies to davie, who knows his stuff, but his assertion could cause confusion.)
Locrian mode can be regarded as a "half-diminished" mode, because a 7th chord built on its root is a half-diminished (m7b5) chord. (Eg, B-D-F-A from C major.)

But the "diminished scale" (in the conventional sense) is something different. It has 8 notes (octatonic), and runs WHWHWHWH. Sometimes called the "whole-half diminished" (for obvious reasons) it has just one other mode, called (guess...) the "half-whole diminished" - HWHWHWHW.
Jazz musicians use the WH dim scale to solo over dim7 chords, and the HW dim to solo over 7b9 chords.
A dim7 chord is the natural VII chord in a minor key, and a 7b9 is the natural V chord. (Derived from harmonic minor in each case, but jazz musicians don't seem to like using harmonic minor to improvise with... )
Eg, in key of C minor, the V chord is G7b9 (G-B-D-F-Ab) and the VII chord is Bdim7 (B-D-F-Ab... notice the similarity?). The C harmonic minor scale would fit both, but a jazz dude is more likely to choose the G HW dim or B WH dim scales - which are the same set of 8 notes:
G Ab A# B C# D E F.
Just to add to davie's reply:
"Parallel" means sharing the same root note. So C minor (C aeolian or C natural minor) would be parallel to C locrian (or C major or C dorian, etc).
C aeolian is relative to D locrian (not B locrian) and any other mode of the Eb major scale.

As davie says, any relative mode can be played against any other - because they are all the same 7 notes! (It's hardly worth thinking of relative modes as different scales at all.)
With parallel scales it's trickier - because they each contain at least one "wrong note" relative to the others.
Eg, we are very familiar with the sound of a parallel minor scale over a major key - that's the blues! But other parallel scales (being less familiar) are likely to sound more "wrong".
If only one or two notes are different that might be OK.
Eg, for C major (ionian), C mixolydian and C dorian are very familiar bluesy alterations, containing b7 and/or b3 respectively.
C lydian is also familiar in jazz improvisation, which means raising the 4th of C major (F# instead of F). (Only over a C chord, mind, not any other chord in the key.)
But C phrygian and C locrian modes are going to sound more "off" against a C major tonality.
That may not mean "wrong" or "bad" (if you want a "wrong note" sound, then that's good!).

A more musical-sounding application of parallel modes is to write a sequence using chords from those modes, alongside chords from a basic major (or minor) key - and then just use the appropriate scales when playing over those chords.
Eg, a chord sequence in C major (C, F, G, Am, Em, Dm or any combination) could include chords like Bb, Ab, Eb or Fm (from C minor/aeolian), or Db or Bbm (from C phrygian or locrian). Or indeed (going in the other direction) D major from C lydian.
It takes skill to weave a large number of these together so the whole thing works, but anything is possible. (Tip: start by borrowing just one or two chords from a parallel mode. Don't overdo it to start with....)

Thanks a lot to both of you for explaining it all to me. I had searched for some info about this stuff on Google and YouTube but strangely enough didn't find anything. I could have used the wrong search words perhaps.

Anyway, I'll have to go through this chunk of info and try it on the guitar.

I've got one last question, if you don't mind. So, are these techniques used much in Metal?

These techniques are definitely used in metal often. Alexi Laiho loves diminished sweeps. Steve Vai has used all 7 modes in his recordings (and some other odd ones, I'm sure). Some bands aren't even aware of what they're doing, but they still use odd modes (Opeth, anybody?). And holy shit... just listen to Tool. Mastodon is another band that fucks with weird keys in their writing (but not as much as Tool, mind you). And if you're asking about relative keys used in metal, I'm quite sure this is very common.

If you have any other questions, I'm taking my second semester of Harmony class in college... and although its kicking my ass I'm still learning quite a lot about all these concepts.

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Well parallel harmonies are used all the time in metal. I'm sure many are using parallel keys over their progressions especially since much metal is power chords which can be major or minor, so it prob just slips by my ear.

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tr00

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Thanks for the replies, everyone.

So, just to recapitulate...

When soloing over a riff which is based on a certain scale, one can obviously solo using that same scale (or mode) on which the riff is based. Or else, there are these relative/parallel modes where one can use different modes to solo over a riff in order to add more 'flavor' and make it sound more interesting.
This is what I understand by the concept of relative/parallel modes. I don't know whether I'm mistaken or not.

Could anyone confirm whether the above is correct or not, please?

That is correct.

Also realize that it's not just parallel keys that you can play out of. Many keys share common chords and chords on the IV and V can be major, minor, or dominant 7th chords. So that opens so many keys over the same progressions.

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Thanks again, man. I have to go over these things. I shouldn't have asked about them really. I'm still not at that stage yet. Hopefully, it won't be long 'til I come to them.