I've run into a quirk in a piece I'm writing, something I've never had to deal with—any ideas?:
The piece is in 4/4. One bar has an extra half-beat (with 18 sixteenth notes rather than 16).
4.5/4 = 9/8, so it seems like I can switch to 9/8 time there, right?
But what about tempo? I've indicated a metric tempo at the start of the piece—but in 4/4, each quarter note gets one beat, and in 9/8, each eighth note gets a beat. So at the same tempo, you're suddenly going twice as fast, right?
Do I solve this by putting "metric modulation" symbols before and after the 9/8 bar? E.g., "[quarter note] = [half note]", then "[half note] = [quarter note]"? Or do I have that turned around? (Or considering this bar's contents, would "[sixteenth note] = [eighth note]", etc., be clearer?)
Or should I simply enter a new metronome value—from "[quarter note] = 80" to "[quarter note] = 40", then back?
Hope this makes sense. Thanks!