In popular music, half time is a type of meter and tempo that alters the rhythmic feel by essentially doubling the tempo resolution or metric division. Thus 4
4 approximates 8
8. It is not to be confused with alla breve or odd time. Though notes usually get the same value relative to the tempo, the way the beats are divided is altered. While much music typically has a backbeat on quarter note (crotchet) beats two and four, half time would increase the interval between backbeats to double, thus making it hit on beats three and seven (counted out of an 8 beat measure [bar], common practice in half time):
1 2 3 4 1 2 3 4 1 2 3 4 5 6 7 8 1 2 3 4
A classic example is the half-time shuffle, a variation of a shuffle rhythm, which is used extensively in hip-hop and some blues music. Some of the variations of the basic groove are notoriously difficult to play on drum set. It is also a favorite in some pop and rock tunes. Some classic examples are the Purdie Shuffle by Bernard Purdie which appears in "Home At Last" and "Babylon Sisters", both of which are Steely Dan songs. "Fool in the Rain" by Led Zeppelin uses a derivation of the Purdie Shuffle, and Jeff Porcaro of Toto created a hybridization of the Zeppelin and Purdie shuffles called the Rosanna shuffle for the track "Rosanna".
It is important to realize that while in half time, the feel of notes are chopped in half, but the actual time value remains the same. For example, at the same tempo, 8th notes (quavers) would sound like 16ths (semiquavers). In the case of the half time shuffle, triplets sound like 16th note (semiquaver) triplets, etc. By preserving the tempo, the beat is stretched by a factor of 2.