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What is the connection between time-signature, beat, and tempo? Mainly time-signature and tempo. Tempo is beats-per-minute I know, but does the time-signature affect it?

For example, in a 120bpm tempo, are note durations of 4/4 time-signature different from 2/4 time-signature? Or how about 4/4 with 6/8? Or is it merely just for adjusting/displaying the notes per measure?

Some of you may be wondering why I am confused. This is because, isnt the bottom part of a time-signature denote which notes are considered as beats? So, if 4/4 at 120bpm = 120 quarter beats per minute, then how much will a 6/8 (8th notes are considered as beats) have as beats per minute? Theoretically, I know that this shouldnt be the case, because well, Tempo IS Beats-Per-Minute.

Thanks!

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3 Answers 3

up vote 6 down vote accepted

Time signatures are primarily for notational purposes. Beat, tempo, and meter all describe a certain thing about the music, but the time signature is just how that's codified when it's written down.

As you know, Tempo is the frequency of the beat, and Beats are a kind of rhythmic emphasis that happens at regular intervals in most music. Meter is an important term--that tells us how each beat is subdivided (i.e. in two or in three) and how to group beats into larger chunks, also at regular intervals.

Time signatures, plus information about tempo, tells us how to get all of that information from notes written on the page. A quarter note alone has very little meaning until we contextualize it in terms of what note value the beat is assigned to and what the frequency of beats is.

You are correct in noticing that there is overlap between tempo markings and time signatures. That is because, while there are some conventions for how they usually relate, these conventions can be broken.

Consider 4/4 time with a tempo marking of q = 60 (bpm). This one is simple, there are sixty quarter notes per minute, and four quarter notes per measure. But what if the tempo marking was h (half note) = 60? There's no hard and fast rule that says the tempo marking has to be equivalent to the time signature (and in fact in 6/8, it rarely is), but in that case, there are still four quarter notes to each measure, it's just that the tempo is being given in how many half notes there are per minute.

Tempo is usually given with a note duration. If that duration is missing, then you can usually assume that it is referring to the bottom part of the time signature. But it is fairly rare to just see a number at the top of the page without any context. In the example you give, there is no note value assigned to the beat, so you would assume that it is referring to the quarter note for time signatures of 4/4 and 2/4.

For 6/8, things get a little bit hairy. This time signature always means that there are six eighth notes per measure, but not always does the eighth note get the beat! 6/8 is most commonly used to refer to a duple meter with a triple subdivision. This means that a dotted quarter note would get the beat, and each beat would be divided into three eighth notes. Most American folk songs fit this model (think about how you would write down "Pop Goes the Weasel"), and 6/8 time is used to avoid writing a triplet figure over every subdivided beat. 6/8 tempo markings are usually written as q. (dotted quarter) = x, but they occasionally will be e (eighth note) = x, signifying that you have six beats per measure.

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So can I just make sure, Time-Signatures are usually just for display purposes? And that for example, playing a music at 4/4 time signature at 120bpm will result in same total playing time if changed to 8/8 at 120bpm? Thanks! –  user488792 Jul 4 '11 at 6:27
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Time signatures are used to contextualize the notation and give information about meter. And yes, those two examples would be the same duration AS LONG AS THE TEMPO IS MARKED q = 120 for both examples. BPM only tells you musical information, it doesn't tell you what notation duration is the beat. –  NReilingh Jul 4 '11 at 14:45
    
Thanks that cleared it up for me! I got confused 'cause I read a paper that correlates the time-signature as the basis for the tempo. –  user488792 Jul 4 '11 at 15:56
    
There is some discussion that suggests that certain time signatures imply faster tempi than others, for example 6/8 is usually faster than 3/4 (think "Irish Washerwoman" vs. "Tennessee Waltz"). However, this would be shown in the metronome marking. By the way, metronome markings often differ in, say, different editions of Chopin Etudes or whatever. The composer usually doesn't put any. On the other hand, time signatures are absolutely required (unless you are Erik Satie) and not subject to change by editors. –  BobRodes Feb 6 at 18:24
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For example, in a 120bpm tempo, are note durations of 4/4 time-signature different from 2/4 time-signature?

If in both cases the quarter note = 120 bpm, then no - the duration is the same.
Time Signatures such as 4/4 are used for notation. They do not describe the tempo, which is a physical (aural) phenomena. Tempo can be represented various ways: with words (adagio, allegro, etc) and a more precise bpm value. Bpm will always define what duration is given as the beat. For example:

quarter note = 120 bpm
half note = 60 bpm

You won't (shouldn't) ever see just "120 bpm". Too many assumptions can be made from this.

Time signatures are not used to convey tempo.
Tempo, is not used to convey time signatures.

Meter was described well by NReilingh.

Hope this helps!

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Wikipedia entries on Tempo and Meter are informative on this topic.

A short answer is that tempo specifies the speed of playing, meter specifies how a score is logically divided into measures (bars) and beats, and that there are rules about how they interrelate but these rules have a bit of fuzziness:

  • For simple meters, the lower number of the time signature is the beat value, that corresponds to the BPM of the tempo.
  • For compound tuple meters (e.g. 6/8) the beat value is typically 3 times the lower number of the time signature, which is the same as the "dotted value of twice". In the case of 6/8, this is three eighths, or a dotted quarter.
  • If the tempo is noted with an explicit note value (e.g. Tempo: 120 = ♩), then this trumps the above rules.
  • If tempo is specified by name (e.g. Allegro), the precise BPM is less significant than the ballpark BPM, which is fuzzily influenced by the type of piece and its cultural associations, but the above rules still apply.
  • If the tempo is significantly fast or slow, common sense may be applied that the BPM applies to half/double the above logic.
  • For complex meters (e.g. 2+2+2+3/8), the above rules presumably apply, but at that point, the musician probably has more context than any rules can provide.

In music, all rules are meant to be broken. For instance, John Cage's 4'33" is traditionally notated as having a tempo of 60 BPM, but is frequently performed at 1/3 this speed.

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Is that the piano version of the Cage, or one of the many orchestrated versions…? –  Bob Broadley Apr 11 at 16:58
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I am most familiar with the version for solo Triangle. I'm a trianguloutist. (This is my neighbor's favorite piece!) –  Jason Boyd Apr 11 at 17:03
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