For popular music, you can determine the time signature by listening to the rhythm section, especially the drum kit and bass. These two instruments typically carry the musical pulse. You can figure out the time signature’s note value (lower number) by listening to the subdivisions of the pulse, and you can figure out the time signature’s note count (upper number) by listening for the repetition of the pulse.
The beat varies greatly from genre to genre, but there are a few handy generalizations to help you find the pulse. Usually the easiest way is to listen for the hi-hat, which consistently carries the pulse in most popular music. Listen for a steady pattern like one of these:
- tick, tick, tick, tick (quarters/crotchets)
- tick-tick, tick-tick, tick-tick, tick-tick (square eighths/quavers)
- tick-tick-tick, tick-tick-tick, tick-tick-tick, tick-tick-tick (triplets)
- tick . . . tick-tick . . . tick-tick . . . tick-tick (shuffle/swing)
The “square” patterns are played evenly or with a regular accent every two, four, or eight ticks of the hi-hat, and they almost always indicate a time signature in 4. Triplet, shuffle, and swing patterns sometimes use compound time signatures, although it’s also very common to write them in 4 with an indication to play eights with triplet or swing feel. (It’s hard to go wrong by writing a popular music score in 4 – it’s by far the most common signature value, and as others have noted, it’s usually trivial to convert to equivalents.)
Once you have the basic pulse from the hi-hat, you can use the bass and snare to find the count. The convention for most popular music is to carry the downbeat in bass (guitar or drum) and the backbeat in snare. Ignoring fills and syncopation, you should find a steady pattern like “thump, hit, thump, hit.” The thumps mark downbeats and the snare hits mark backbeats. If you find that pattern exactly, the piece is in 4/4 time. Otherwise, count how many beats it takes the whole pattern to repeat. If the count is even, divide it in two until you get to an odd number or 4. For example, if you hear “thump, hit, hit, thump, hit, thump, hit” repeated, the song is in 7/4 time (grouped into 3/4 + 4/4). If you hear “thump, thump, hit, thump, hit, hit” repeated – a count of six – the song is in 3/4 time.