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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!

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  • 1
    In 9/8, there are three dotted-quarter beats in a bar. It's not clear in your question what you actually want to achieve with the 9/8 bar (is each eighth note the same throughout the piece, or do you want the 9/8 bar to take the same time as a 4/4 bar?)
    – Andrew Leach
    Commented Jun 16, 2022 at 7:45
  • If there are indeed 18 notes, could you play them as tuplets, retaining 4/4?
    – Tim
    Commented Jun 16, 2022 at 9:24
  • "So at the same tempo, you're suddenly going twice as fast, right?" There is a notational convention for specifying that the eighth note of the new meter has the same duration as the eighth note of the old meter, so no, not necessarily.
    – phoog
    Commented Jun 16, 2022 at 14:37
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    I'm a little confused about how long you want the 9/8 bar to be. First, you write that "one bar has an extra half-beat," which makes it sound like you want the 9/8 bar to be only slightly longer than each 4/4 bar, with an eighth note in the 9/8 bar equal to an eighth note in each 4/4 bar. But then you write that you're considering various metric modulation and metronome marks, which makes it sound like you want the 9/8 bar to be over twice as long as each 4/4 bar, with an eighth note in the 9/8 bar equal to a quarter note in each 4/4 bar. Which one are you looking for?
    – Tanner Swett
    Commented Jun 16, 2022 at 15:59
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    "So at the same tempo, you're suddenly going twice as fast, right?" – If the length of a beat stayed the same when moving from 4/4 to 9/8, then it would sound like the musician is suddenly playing half as fast, not twice as fast. (But my understanding from reading the answers below is that that's moot, because the length of a quarter note, not the length of a beat, stays the same when moving from 4/4 to 9/8.)
    – Tanner Swett
    Commented Jun 16, 2022 at 16:02

4 Answers 4

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Here's some possibilities.

If the note grouping is as clear as in my example, maybe the metric modulation is unnecessary in A.

D is acceptable in today's music. But you will find it a challenge to produce in many notation programs!

Is there actually an extra note? Maybe E or F are what you really need.

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    I like [A] the best.
    – Brian THOMAS
    Commented Jun 16, 2022 at 12:35
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    For me [C] appears to be the best option. I'm reminded for some reason of one of the movements of Carmina Burana.
    – JimM
    Commented Jun 16, 2022 at 13:36
  • I'd vote for [E] or [F], personally, though it might depend on the situation. Avoiding time signature changes when you just want to extend a measure a bit longer seems like the simplest solution. If you want to be really precise, you could just include a textual note there indicating exactly how long to hold the fermata.
    – Darrel Hoffman
    Commented Jun 16, 2022 at 16:00
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    @Darrel Hoffman Of course, you can only vote for E or F if that's what the music DOES... Maybe there really are 4½ in-tempo beats in that bar!
    – Laurence
    Commented Jun 16, 2022 at 17:18
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    I could see someone interpreting C as triplets with the entire measure lasting a single beat, the same length as each beat in previous measures. Would that interpretation be incorrect?
    – Nigel
    Commented Jun 16, 2022 at 23:47
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In addition to other answers.

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?

I guess you are used to define tempo in "beats per minute", but in sheet music it is typically specified as number of notes of given value – e.g. quarter notes – per minute. Tempo specified this way does not change.

Also, if 9/8 is in fact a compound meter of 4/4 + 1/8, possibly the beat base doesn't even change, except for the time when it needs to shift by an eight note.

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Well, that depends. Time Signatures imply an inherent beat structure. 4/4 will have 4 beats of 1/4th notes. 9/8 as three beats each made up of 3 1/8th notes or one dotted 1/4th. Depending on what your music actually does this might be exactly what you want, or it might be confusing. Other options might include 4/4+1/8 or even simply 18/16.

About the tempo: Tempo is not given in beats per second, but in a specific duration value per second. Common modern consensus is that this tempo remains the same even if time signature changes happen. This would have been different in baroque time, which is why there is some old practise of putting the tempo indication L’istesso tempo (the same tempo) to indicate that the tempo does not change.

From what you’re saying you seem to imply you do not actually want this, but you want to have this 9/8 measure to be played in half the tempo of the 4/4 measures. This could simply be done by putting eighth = quarter as tempo indication.

But why not simply use one 9/4 with double note values instead? This way you would not induce any confusion by suddenly taking half the tempo for a single measure.

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  • "Key Signatures imply an inherent beat structure" - I think you mean time signatures?
    – Mark Beadles
    Commented Jun 17, 2022 at 16:37
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    @MarkBeadles Fugue, you’re right!
    – Lazy
    Commented Jun 17, 2022 at 19:13
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You're overthinking this.

"and in 9/8, each eighth note gets a beat"

  1. I could say "yes, and those beats are twice as fast" and be done with it. You get precisely the effect you want.
  2. But really, music theory does not have beats that are independent of note values. That only happens in DAWs / sequencers. Normally the beginning of a piece indicates how many quarter or eighth notes there are per minute, and that keeps holding, even with time changes. So: do not indicate anything. The player will figure "eighth note here is eighth note there" and play it correctly.
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