In music and music theory, the beat is the basic unit of time, the pulse[clarification needed] (regularly repeating event), of the mensural level (or beat level). The beat is often defined as the rhythm listeners would tap their toes to when listening to a piece of music, or the numbers a musician counts while performing, though in practice this may be technically incorrect (often the first multiple level). In popular use, beat can refer to a variety of related concepts including: pulse, tempo, meter, specific rhythms, and groove.
Rhythm in music is characterized by a repeating sequence of stressed and unstressed beats (often called "strong" and "weak") and divided into bars organized by time signature and tempo indications.
Metric levels faster than the beat level are division levels, and slower levels are multiple levels. Beat has always been an important part of music. Some music genres such as funk will in general de-emphasize the beat, while other such as disco emphasize the beat to accompany dance
As beats are combined to form measures, each beat is divided into parts. The nature of this combination and division is what determines meter. Music where two beats are combined is in duple meter, music where three beats are combined is in triple meter. Music where the beat is split in two are in simple meter, music where the beat is split in three are called compound meter. Thus, simple duple (2/4, 4/4, 2/2, etc.), simple triple (3/4), compound duple (6/8), and compound triple (9/8). Divisions which require numbers, tuplets (for example, dividing a quarter note into five equal parts), are irregular divisions and subdivisions. Subdivision begins two levels below the beat level: starting with a quarter note or a dotted quarter note, subdivision begins when the note is divided into sixteenth notes.
Downbeat and upbeat
The downbeat is the first beat of the bar, i.e. number 1. The upbeat is the last beat in the previous bar which immediately precedes, and hence anticipates, the downbeat. Both terms correspond to the direction taken by the hand of a conductor.
This idea of directionality of beats is significant when you translate its effect on music. The crusis of a measure or a phrase is a beginning; it propels sound and energy forward, so the sound needs to lift and have forward motion to create a sense of direction. The anacrusis leads to the crusis, but doesn't have the same 'explosion' of sound; it serves as a preparation for the crusis.
An anticipatory note or succession of notes occurring before the first barline of a piece is sometimes referred to as an upbeat figure, section or phrase. Alternative expressions include "pickup" and "anacrusis" (the latter ultimately from Greek ana ["up towards"] and krousis ["strike"/"impact"] through French anacrouse). In English, anákrousis translates literally as "pushing up". The term anacrusis was borrowed from the field of poetry, in which it refers to one or more unstressed extrametrical syllables at the beginning of a line.[
On-beat and off-beat
In typical Western music 4
4 time, counted as "1 2 3 4, 1 2 3 4...", the first beat of the bar (downbeat) is usually the strongest accent in the melody and the likeliest place for a chord change, the third is the next strongest: these are "on" beats. The second and fourth are weaker—the "off-beats". Subdivisions (like eighth notes) that fall between the pulse beats are even weaker and these, if used frequently in a rhythm, can also make it "off-beat".
The effect can be easily simulated by evenly and repeatedly counting to four. As a background against which to compare these various rhythms a bass drum strike on the downbeat and a constant eighth note subdivision on ride cymbal have been added, which would be counted as follows (bold denotes a stressed beat):
- 1 2 3 4 1 2 3 4 —play eighth notes and bass drum alone (help·info)
- 1 2 3 4 1 2 3 4—the stress here on the "on" beat play (help·info) But one may syncopate that pattern and alternately stress the odd and even beats, respectively:
- 1 2 3 4 1 2 3 4 —the stress is on the unexpected" or syncopated beat play (help·info)
So "off-beat" is a musical term, commonly applied to syncopation that emphasizes the weak even beats of a bar, as opposed to the usual on-beat. This is a fundamental technique of African polyrhythm that transferred to popular western music. According to Grove Music, the "Offbeat is [often] where the downbeat is replaced by a rest or is tied over from the preceding bar". The downbeat can never be the off-beat because it is the strongest beat in 4
4 time. Certain genres tend to emphasize the off-beat, where this is a defining characteristic of rock'n'roll and Ska music.
source : wikipedia Beat music
source 2 : Download Beat on Beatestan.com