A track sheet is the document that says what is on each channel of a multitrack recording. In its plainest form it is a numbered list. In practice it is the most compressed record of a session that exists, and someone who can read one can walk into an unfamiliar project and be useful within a few minutes.
What is actually on it
At minimum: the track number, what was recorded on it, and which take is the keeper. A well-kept sheet adds the microphone used, the preamp, notable settings, and a note about anything unusual. Dates matter more than people expect, because they let you reconstruct which sessions belong together when the file names have stopped being informative.
The genuinely valuable entries are the ones that record intent. "Room mic, far, for the bridge only" tells you something no waveform will. So does "DI kept in case the amp does not work" and "scratch vocal — keep for timing reference".
Reading the structure
Start by looking at what got the most channels. A kit with eight microphones and a bass on one DI tells you where the attention went. A vocal with four comped takes and a guitar with one tells you which performance was hard to get. This is not always what the artist would tell you, and it is usually more honest.
Then look for gaps. A session with no room microphones was probably recorded somewhere that did not offer any, which tells you the ambience will have to be added and that the close sounds need to survive that. A session with no DI on a bass means the amp sound is the only sound, and reamping is off the table.
Take numbers tell a story
A part that reached take twenty-three was difficult, and the difficulty is usually audible. It might be a tempo the player could not settle into, an arrangement that changes underneath them, or a part written outside their comfort. When you find that in a track sheet, listen to the early takes as well as the keeper. The first take is frequently looser and better, and the later ones are frequently more accurate and stiffer. Which one serves the song is a real question and not always the one that was marked.
Naming conventions are documentation
Channels named "Audio 1" through "Audio 24" are a decision to make the next person guess. It costs nothing during the session to name them properly and it costs an hour later to work them out. The convention itself matters less than its consistency: pick one, use it for everything, and make it sortable so related tracks group together.
Two habits that repay themselves: put the source first, so that "Gtr — rhythm L" and "Gtr — rhythm R" end up adjacent, and never reuse a name for a different thing between sessions. A track called "Vox" that means lead vocal in one session and background vocals in another is worse than no name.
What to write down that people usually do not
The tuning, if the session is not at concert pitch. The tempo, including whether the take followed a click. Any signal processing that was printed rather than monitored, because that cannot be undone. Which headphone mix the performer was hearing, if it was unusual. And the reason for anything strange, because in six weeks nobody will remember why the second snare microphone was polarity-inverted.
The sheet is for the future, not for now
During a session everyone knows what everything is. That is exactly when the sheet feels unnecessary and exactly when it must be written. Three months later, working from files alone, the difference between a good sheet and no sheet is the difference between an afternoon and a day.
It also matters when someone else does the work. A mix engineer receiving stems with a proper sheet can make decisions on the first pass instead of asking questions for two days. This is one of the few pieces of session discipline that produces a measurable saving in time and money, and it takes about fifteen minutes.
If you are handed one
Read it before you open the session. Form an expectation of what you are about to hear, then check it against the audio. The places where the sheet and the recording disagree are the places worth asking about, and they are usually where the interesting decisions were made.