In music, time is measured in beats. A beat, then, is a unit of time. But beat is also the word for the rhythmic impulse whether felt, understood, or indicated with a physical gesture from a hand, foot, or conductor's baton that marks the start of each unit of time. It can also be the word for the physical gesture itself, as in, "That conductor has a very clear beat."
A beat is a regular, repeated impulse, like a pulse, but like a pulse it's also variable: fast music has a fast beat the time intervals between the impulses are short and slow music has a slow beat. Beats are grouped into measures, so that one speaks of "three beats to the measure," for example, or "four beats to the measure." In any given piece, a note value such as the eighth note, quarter note, or half note is assigned as the value of the beat. For example, "2/4 time" means that there are two beats per measure and that the value of the beat is a quarter note (indicated by the "4"). And "6/8 time" means that the beat is an eighth note and there are six beats per measure.
The double meaning of beat impulse and duration can sometimes lead to confusion. To start at the beginning of a measure and "hold a note for three beats" means to hold the note for the length of time covered by three complete beats. To hold a note "until the third beat" is another way of saying to hold it for two complete beats.
Here are a few common terms that have to do with beat:
ON THE BEAT: When a note or sound coincides with a beat, that is, with the beginning of a beat, it is said to be "on the beat."
DOWNBEAT: The downbeat is the first beat of a measure. It is also the strongest beat, where the greatest "weight" or rhythmic emphasis normally falls although music may be written in such a way as to shift that emphasis. A downbeat, like any other beat, may be "empty," meaning empty of sound, while the beat itself is still counted and felt.
The word downbeat may also refer to the gesture that a conductor gives on the downbeat of a measure.
UPBEAT: An upbeat is a beat that occurs just before a downbeat, but the term is used primarily when the beat in question has a preparatory function, when it "belongs," in a sense, to the following downbeat. In "The Star-Spangled Banner," for example, the opening word, "Oh," comes on the upbeat to the first measure, and "say" comes on the downbeat. The word upbeat may refer either to a beat or to an actual note or group of notes. If a certain note comes on the upbeat, in other words, then it's also correct to say that that note is an upbeat. Musicians very often use the colloquial term pickup to describe such a note (or group of notes), as in, "Do you have a pickup to the third measure, or do you start right on the downbeat?"
The word upbeat may also refer to the gesture that a conductor makes on the upbeat of a measure, usually as a preparatory signal for the orchestra.
OFFBEAT: In the most general sense, an offbeat is any beat that is not the downbeat of a measure. It implies a "weak," or unstressed beat, often a beat that occurs between two stronger beats. (Like upbeat, the term offbeat may refer either to the beat itself or to a note that occurs on the offbeat.) Think of a pattern like "Boom-chick, Boom-chick, Boom-chick." The "chicks" are offbeats. To thicken the plot, however, if the "boom-chicks" are grouped two to a measure, "Boom-chick, boom-chick/Boom-chick, boom-chick/Boom-chick, boom-chick," then the lowercase booms, while "on" the second beat of each measure, are also offbeats, because the second beats are weaker than the downbeats. Similarly, in the pattern "Oom-pah-pah, Oom-pah-pah, Oom-pah-pah," the "pah"s are all offbeats. When a composer chooses to place an unexpected stress on the offbeat, the result is called syncopation.
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