MIDI beat clock, or simply MIDI clock, is a clock signal that is broadcast via MIDI to ensure that several MIDI-enabled devices such as a synthesizer or music sequencer stay in synchronization. Clock events are sent at a rate of 24 pulses per quarter note. Those pulses are used to maintain a synchronized tempo for synthesizers that have BPM-dependent voices and also for arpeggiator synchronization.
MIDI beat clock differs from MIDI timecode in that MIDI beat clock is tempo-dependent.
Location information can be specified using MIDI Song Position Pointer (SPP, see below), although many simple MIDI devices ignore this message.
MIDI beat clock defines the following real-time messages:
MIDI also specifies a System Common message called Song Position Pointer (SPP). SPP can be used in conjunction with the above real-time messages for complete sync. This message consists of 3 bytes; a status byte (decimal 242, hex 0xF2), followed by two 7-bit data bytes (least significant byte first) forming a 14-bit value that specifies the number of "MIDI beats" (1 MIDI beat = a 16th note = 6 clock pulses) since the start of the song. This message only needs to be sent once if a jump to a different position in the song is needed. Thereafter only real-time clock messages need to be sent to advance the song position one tick at a time.
Pulses per quarter note (PPQN), also known as pulses per quarter (PPQ), and ticks per quarter note (TPQN), is the smallest unit of time used for sequencing note and automation events. [1]
The number of pulses per quarter note is sometimes referred to as the resolution of a MIDI device, and affects the timing of notes that can be achieved by a sequencer. [2] [3] If the resolution is too low (too few PPQN), the performance recorded into the sequencer may sound artificial (being quantised by the pulse rate), losing all the subtle variations in timing that give the music a "human" feeling. Purposefully quantised music can have resolutions as low as 24 (the standard for Sync24 and MIDI, which allows triplets, and swinging by counting alternate numbers of clock ticks) or even 4 PPQN (which has only one clock pulse per 16th note). At the other end of the spectrum, modern computer-based MIDI sequencers designed to capture more nuance may use 960 PPQN and beyond.
This resolution is a measure of time relative to tempo since the tempo defines the length of a quarter note and so the duration of each pulse. The resulting PPQN per MIDI-Clock is thus related to the TimeBase in Microseconds defined as 60.000.000 / MicroTempo = Beats per minute. [4]
MIDI is a technical standard that describes a communication protocol, digital interface, and electrical connectors that connect a wide variety of electronic musical instruments, computers, and related audio devices for playing, editing, and recording music.
MIDI time code (MTC) embeds the same timing information as standard SMPTE timecode as a series of small 'quarter-frame' MIDI messages. There is no provision for the user bits in the standard MIDI time code messages, and SysEx messages are used to carry this information instead. The quarter-frame messages are transmitted in a sequence of eight messages, thus a complete timecode value is specified every two frames. If the MIDI data stream is running close to capacity, the MTC data may arrive a little behind schedule which has the effect of introducing a small amount of jitter. In order to avoid this it is ideal to use a completely separate MIDI port for MTC data. Larger full-frame messages, which encapsulate a frame worth of timecode in a single message, are used to locate to a time while timecode is not running.
Rhythm generally means a "movement marked by the regulated succession of strong and weak elements, or of opposite or different conditions". This general meaning of regular recurrence or pattern in time can apply to a wide variety of cyclical natural phenomena having a periodicity or frequency of anything from microseconds to several seconds ; to several minutes or hours, or, at the most extreme, even over many years.
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A metronome is a device that produces an audible click or other sound at a uniform interval that can be set by the user, typically in beats per minute (BPM). Metronomes may also include synchronized visual motion, such as a swinging pendulum or a blinking light. Musicians—and others including dancers, athletes, and health professionals—often practise with a metronome to improve their timing, especially the ability to maintain a steady tempo with a regular beat or pulse. Composers and conductors often use numerical metronome markings to communicate their preferred tempos to musicians preparing for a performance.
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In music theory, the pulse is a series of uniformly spaced beats—either audible or implied—that sets the tempo and is the scaffolding for the rhythm. By contrast, rhythm is always audible and can depart from the pulse. So while the rhythm may become too difficult for an untrained listener to fully match, nearly any listener instinctively matches the pulse by simply tapping uniformly, despite rhythmic variations in timing of sounds alongside the pulse.
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