Whether you are working on a piece single-handedly or in collaboration with others, as a musician, you will come across a click track at some point. So, what is a click-track? Its an audio track, with beats at regular intervals, that you can hear as you would when a metronome is played, as well as visualize when looking at the waveform.
So, why not use a metronome itself? Why is a click track indispensable? Its simple :
Of the two points above, the second one is much more important, in that, when collaborating remotely, each musician needs to still sync up with the rest of the group, when starting new sections in the song, or playing their solos over other’s backing, hence this particular track is of vital importance. When a vocalist, for example, expressively extends notes, the rest of the band should still be able to move together without missing a beat, otherwise any tension built up by the vocalist loses its impact. Delivering on the beat, has its own value.
Now, it is common, that a particular track may be recorded more than once, as the artist may feel that one part of the section sounds better in one track, while another section sounds good in subsequent recordings of the same track. In this case, it is common to cut and paste tracks from various sources, so that the audio sounds good. Bear in mind, when doing this, if you dont align each cut track to the cue points on the original click track, the next musician who needs to work with your track will find it very hard to accompany your track. Remember, all you tracks need to be aligned with each-other for a tight piece.
It is good practice, to have the lead musician design the click track, with its various changes and cue points, for others than let each musician individually figure out where the changes occur. Every guess has its inbuilt error which leads to subsequent avoidable rework. It is better in this case to get it right the first time than learn from mistakes.
I hope this helps most performing musicians understand elementary aspects of being a studio musician and helps making music more fun.