A click track is a file with a beat on it. Everything else about a metronome is a matter of getting the beat in exactly the right place and making the sound easy to hear through headphones while something loud is happening.
Placement
Every click is placed by rounding its own beat time to the nearest sample. Adding one beat’s worth of frames to the previous click would be simpler and wrong: rounding error accumulates, and by bar 300 the click has walked away from the grid.
The difference matters for anything that gets edited to the grid afterward.
Subdivision
Quarters are the default. Eighths help with anything fast enough that the quarter feels sparse, triplets for compound time, sixteenths for programming and tight editing.
The accent stays on the downbeat whichever subdivision the clicks land on, so the bar is always readable.
Click sounds
Wood is a short pair of partials with a noise transient, around 12 ms. It cuts through a loud mix better than a sine, which is what most sessions need.
Beep is a single 1 kHz tone at 35 ms. It is the easiest to hear at very low levels and the easiest to ignore when it bleeds into a microphone.
Rim is 6 ms and mostly noise. Use it when the click is bleeding into an open mic and you need something that disappears fast.
Level and accent
The click sits at whatever level you set, and the accent defines the peak. Set the level for the headphone mix rather than for the file: a click at -6 dBFS is loud, and most sessions want it 15 to 20 dB below the music.
Bleed is the usual reason a take gets rejected. A quieter click with a shorter decay bleeds less than a loud one turned down at the desk.
Length
Length is set in bars rather than seconds, so the file ends on a bar line. A 32 bar file at 4/4 and 120 BPM is 64 seconds; change the tempo and the bar count holds while the duration follows.
Add a couple of bars at the front if you need a count-in that the take can start after.