DRUMMER CAFE

it's when a song transitions from one tempo to another.  an example is "Jesus is just alright with me" by the Doobie Brothers.

It is the transition from one time signature to another, thus giving the feeling of a tempo shift when none actually takes place.  Anthony Cirone's "Portraits in Rhythm" includes some snare drum etudes where metric modulations takes place.

Right. The tempo stays the same, but what gets the beat (quarter, dotted-quarter, etc.) changes. But once the change has been made, the new realized tempo is different. It can still be in 4/4 or whatever time signature you were originally in.

Once you make the shift, assuming you are staying there and really performing a metric modulation, you can still be in 4/4 because the new "what get's the beat" has been established and can be thought of as the quarter-note.

Let's say I'm playing a groove, it's in 4/4 and 90 bpm. This means the quarter-note gets the beat; 90 quarter-notes in a minute. When I shift, performing a metric modulation, let's say I'm going to let the dotted-eighth-note get the beat. When I do this, the ratio is 3:4; the quarter-notes occur in the span of 4 dotted-eighth-notes. At this point, I'm still thinking 4/4 because I'm just emphasizing or implying where I'm shifting or modulating to. There's still 16 sixteenth-notes in the bar.

Once you do this, if you maintain it, the ear hears a new pulse. We can use some good ol' Algebra to see what the new tempo is ...


Doing the math, we find that if I shift from quarter-note pulse to dotted-eighth-note pulse, the new tempo is 120 bpm.

Since I have shifted, performing the metric modulation, there's no need to relate it to the old meter or tempo. I've established my new pulse, and can notate it in 4/4 or any new meter you want ... but rather than 90 bpm, I'm now at 120 bpm.

In my audio example from the 5-Minute Lesson, I stayed in 4/4, but performed a metric modulation by first letting the dotted-eighth be my new implied pulse, then actually shifting to it permanently, making it equal to my old quarter-note ... time signature wise.