1.4.5. Time, Timeline, and Time-Shifting

There are many ways to measure musical time. The four most popular time scales for digital audio are:

Bars and Beats: Usually used for MIDI work, and called "BBT," meaning "Bars, Beats, and Ticks." A tick is a partial beat.
Minutes and Seconds: Usually used for audio work.
SMPTE Timecode: Invented for high-precision coordination of audio and video, but can be used with audio alone.
Samples: Relating directly to the format of the underlying audio file, a sample is the shortest possible length of time in an audio file. See Section 1.3, “Sample, Sample Rate, Sample Format, and Bit Rate” for more information.

Most audio software, particularly digital audio workstations (DAWs), allow the user to choose which scale they prefer. DAWs use a timeline to display the progression of time in a session, allowing you to do time-shifting; that is, adjust the time in the timeline when a region starts to be played.

Time is represented horizontally, where the leftmost point is the beginning of the session (zero, regardless of the unit of measurement), and the rightmost point is some distance after the end of the session.