the duration is expressed as fractions or multiples of a beat,

rather than as a duration in seconds.

Beats are related to or even synonymous with pulse.

And they're clearly related to tempo,

which is often expressed as beats per minute.

Rhythm then concerns multiples or subdivisions of beats.

It can be expressed symbolically in western notation

in the form of both rests and notes.

So for instance,

all of our western rhythmic durations are related to the whole note,

as it's called in America, or the semibreve, as it's called in Britain.

Semibreve represents the full duration of one bar in 4/4 meter.

We'll come to meter in a little while, but

suffice to say, 4/4 is the most common meter that we come across.

The semibreve can, of course, be subdivided and

these subdivision have different names.

In British nomenclature, for example, we speak of minims, crotchets, quavers, etc.

There are two minims per semibreve.

This is also known as the half note in American parlance.

This is then subdivided into two crotchets,

crotchets are quarter notes in the US and

there are four quarter notes in a whole note, or a semibreve as you might imagine.

Crotchets are then further divided into quavers, eighth notes, and

on into semiquavers, 16th notes, and so on and so forth.

So if you use the American nomenclature, which is derived from the German,

by the way, it's very easy to see how many of a particular rhythm you'll

have in a whole note, as all rhythms are expressed in relation to this.

So let's just recap here and look at the actual notation of these rhythms.

First of all,

we've got the open round note symbol, which is the semibreve or whole note.

This is four beats long in common time, or 4/4 meter.

Again, more on this later.

Then we've got the half note, or minim, the crotchet, the quaver,

and the semiquaver.

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We also have the equivalent rhythms in rests.

Rests are necessary to indicate where a musician stops playing notes.

Most music consists of notes surrounded by space, of course, otherwise musicians

would never get the chance to breathe or rest, and neither would the music.

So first of all, again, the semibreve or whole note rest, the minim or

half note rest, the crotchet or quarter note rest, the quaver,

eighth note rest, and the semiquaver, or sixteenth note rest.

You can see that the quaver and

semiquaver notes are essentially crotchets with little flags on their stems.

Each flag that you add divides the rhythm by two.

So we could further divide semiquavers into demisemiquavers or

32nd notes in American parlance.

And these can be further subdivided into hemdemisemiquavers or 64th notes,

etc., etc.

Now those flags, which we've seen on the quavers of lesser durations,

can actually turn into what we call beams.

We use beams so that we can group notes in twos, fours, eights, etc.

And thereby easily see a beat's worth, or sometimes more, of shorter notes.

This makes it easier to orientate ourselves in the flow of the music, so

we can recognize where the beat boundaries are.

Here's another example.

You can see that the number of flags which we use in the individual notes

is reflected in the number of horizontal beams.

And that adding one more beam is equivalent to adding one more flag,

that is, we're subdividing the rhythm into two.

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