Can someone tell me what interval (chord?) this is?

[warwick.hoy]

I hear it a lot in basslines. I'm not sure if it is an octave and I'm just not hearing it that way. Listen to the bassline as the interval (chord?) in question comes in 36 seconds into the song. He does a little glissando kinda thing with it too. Here is the song.

http://www.last.fm/music/Umphrey%27s+McGee/_/The+Fuzz

P.S. Sorry if this is the wrong forum.

~James

[3506string]

Ab and D together slid half a step lower and back. I hear it a lot on Home Improvement.

[JTE]

I didn't listen, but if it's Ab and D, it's a diminished 5th, also known as a tri-tone. Ab and D are the key elements of either a Bb7 (they're the b7 and the 3rd respectively) or of an E7 (where I'd call the Ab a G# so it's the 3rd of the chord, and the D is the b7).

It's a common blues guitar bit ("Red House" for example), and it's why you can substitute a Bb7 for an E7.

jte

[DocBop]

Using a tritone for a double stop has been done for ages on bass. It is typically used to imply a dominant 7th chord. Either note of a tritone is the 3rd or 7th of a dominant chord. That is why tritone substitutions work.

[onlyclave]

Originally Posted by JTE

It's a common blues guitar bit ("Red House" for example), and it's why you can substitute a Bb7 for an E7.

You should clarify that statement a bit. In a dominant 7 chord the root and the perfect fifth don't add any color. The third and seventh (a tritone apart) are called the "critical tones" because they give the chord color and function. In a II V7 I (or any cyclic 5th progression) the V7 may be substituted with a bII7 chord because the chord members that are the 3rd and 7th in the V7 are also (although enharmonically spelled) the inverted 7th and 3rd of the bII7 chord, plus the downward chromatic root movement sounds good to the ear too. That's why you can substitute a Bb7 for an E7 in some cases.