Sync

Sync is important because it is what aligns the chart with the song. If the sync isn't good enough, players can get frustrated because if they hit the notes to the music, they get poor scores, and if they hit the notes by timing, it doesn't line up with the song. Poor sync makes a chart feel like it was shoddily constructed, and in more extreme cases, it is extremely difficult to even play. Sync is considered to be one of the most mechanical, most objective topics regarding chart making. It should be crystal clear what the chart artist wishes to accomplish through note positioning, so sync is more or less either accurate enough or not accurate enough, and usually not a matter of interpretation and subjectivity. (There are plenty of exceptions to this rule, but they will be discussed in the advanced topics sections.)

There are three major components to sync: offset/gap, BPM, and rhythm.

Offset refers to where the chart starts. Even if everything else is correct, if your offset is off, the entire chart will be shifted a certain amount of time early or late. Getting the offset correct initially is also important because bad offset could cause the sync to be inconsistent later on, so fixing it will become very tedious.

BPM stands for "beats per minute." Almost all songs have a natural pulse that hold the timing of the song together, which is referred to as the beat. BPM is simply an indicator of how fast or slow the pace of the beat is. For some songs, the BPM is fairly constant throughout (a lot of electronically generated music have constant BPM for the whole song, making it easy to sync), while others have BPM that fluctuates, sometimes instant, sometimes gradually. BPM is important because an inaccurate BPM will eventually cause a chart that is initially properly synced to slowly go out of sync due to a drift in timing. Accurate BPM assures that this does not happen; a chart that is initially in sync stays in sync.

The last component is rhythm. Even if you have the right offset and BPM, placing down notes in an incorrect rhythm makes the other two meaningless. This is a little bit more difficult to describe because it's more open-ended, but the idea is that you want to try and follow the rhythmic patterns the way they were intended to be in the music. For example, a rhythmic pattern in 16ths should not have triplet rhythms in it. For the majority of most songs, the rhythm is quite straightforward. However, if the rhythm it should be written as isn't accurate enough, don't hesitate to adjust it using the different rhythmic intervals (such as pushing them forwards or backwards by 48th or 64th notes) instead of by BPM changes or stops. The colorful notes you create will probably look pretty anyways and act as a warning to players that the rhythm is slightly out of place.

Although these are all the standard components that a chart should apply for accurate sync, technically as long as the notes lines up with the song at the correct times, the chart is fine. However, thinking about sync as these components will almost always dramatically make your sync easier to do, fix, and adjust, as well as make your chart look more appealing, organized, and clean. As you get more and more comfortable, try to aim for your sync to be as accurate as humanly possible. Experienced players can detect when the sync is off even by a couple of milliseconds, so if you can afford to hone your sync skill, it is worth it!

When you're working on the sync or checking it, make sure to use both a combination of your own sense of hearing and playtesting, as well as double-checking against the waveform of the recording if you're using an appropriate editor. Lowering the rate and using an assist tick sound can help as well, not only to check sync but also to figure out if the notes are lining up with the sounds you want it to line up with.