I am pretty new to music. One question I have is how do I know how how many bars a line in a song is. For example in Basket Case by Green Day, how do I know how long the first line is other than the number of seconds?
By simple counting. If a song is in 4/4, which covers many, many songs, listen to the beats. Each bar will have a count of four, then a slightly emphasised note heralding the start of the next bar. So, count four for as many times it takes to go from the beginning to the end of a line, that's how many bars long it is. Often the answer is 4, which works for a lot of pop type songs. We rarely count music in seconds, although when recording, the machine will often use seconds and smaller units of time to display where in the music things are.
TL;DR: Usually you just count.
For many cases in modern pop music you just need to count exactly how many beats passed before it starts to kinda repeat itself. But there's a catch. Although beat strengths may sound similar to each other, they differ by their roles in a bar (unless it's a 1/4 or 1/x, which is very rare case). So first that you do is recognize the cycling pattern in the rhythm. That's a bar. Then you count number of beats per each bar, – and here you go! Time signature for this piece is n/4, which means literally "n quarters per bar".
This method covers most cases, but not all of them. You have to keep in mind several things:
- Using this method it may be difficult sometimes to distinguish "2/x" from "4/x" or "3/x" from "6/x" etc.
- Pattern may vary. It means, that time signature for different parts of the piece is different.
- Pattern may cycle over another smaller pattern. This is not so rare in classical music. Possible example of this is "2/4 + 3/8 + 4/4," which means literally "two quarters, then three eights, then four quarters per bar."
- You can't be sure about quarters. Although it usually is "n/4", it may be "n/8" or "n/2". Learn more about this.