From the forum:

Metal riffing is usually most successful when there is a large transfer of energy from one riff to another, as this is how the song communicates.

Multiple riffs or layered riffs in the best metal often manage to achieve complex intertwining tension trade-offs, whether it be the battering complexity of tracks like “Fall From Grace” or poignant riffing of “My Journey to the Stars”. Melody, rhythm, and just about everything play into this structuring of music.

Trophic levels seem to be a good metaphor for this:

       -A-
     ---B---
  -----C-----
-------D-------

(Losing energy as you travel up the food chain)

Something like that. Much like how trophic levels have certain amounts of energy being transferred from one member in the food change to the next, riffs have that power as well. The main difference is that riffs are not locked into certain energy transfers, but rather by manipulating this, we can see varied results.

For example:

If we take a band that has very high net energy transfer, we get something like this.

-------A-------
-------B-------
-------C-------
-------D-------

(Energy is transferred totally from level to level; sturdy structure technique can fail if not enough energy spread throughout. Unlike later FAIL in that it has a large amount of energy that maintains interest.)

In this case, we have a song that transfers all energy from one riff to the next. This tradeoff creates an intense song, maintaining power throughout.

Now let’s take something more complex:

-------A-------
   -----B-----
       --C--
    ----A----

(Repetition of A riff later on is given more poignancy by putting in two riffs which help magnify its later recurrence.)

Now, we begin with a riff, before cycling into a riff with a distinct lack of power in comparison to the first (C), but this riff paves the way for the more powerful riff following it, and to cap it off, the initial riff is repeated, creating a sense of importance.

This structure would be a “journey” as ANUS puts it, as the same riff is used at both the end and beginning, but the last one is more important due to interaction in between. (Mind you that there can definitely be more than 3 riffs, this is just an example.)

Now for ambient, it’s different:

                      -----
              ----            ----
        -------               --------
----------          A           ----------
        -------               -------
                 ----      ----
                      -----

(Different in that the idea is “framed” inside the music, as stated somewhere else on forum)

Now these are the ways you can FAIL.

-A-
-B-
-C-
-D-
-E-
-F-

(Loads of riffs, but there is no journey or real kinetic friction, so something like Necrophagist could be likened to this, “riff buffet”. NO difference in energy levels, and very little to start with)

--A (It's probably C in disguise actually)--
--B--
 -C-

(metalcore, AKA caveman structure. Very little variance, and the small jump in energy from C to B is pretty pathetic anyway)

Metal is interesting in that it can use both the ambient and riff like structure to great effect.

Let me know what you think, what can I fix, I know I ignored some things. Is this an oversimplification?

– razorfield9