Sync rate is your score on a given song. For this achievement, you need 122%.

The highest scoring note is EXACT, but depending on your timing, EXACT will display either in blue or cyan. The thing you have to understand is that cyan EXACTs are worth more percentage points than blue EXACTs. So, to get this achievement, you have to be seeing the lighter coloured lettering almost all the time.

As with all the achievements, you can get this with the songs that come with the base game. You don't need any DLC for this.

I selected Gameboy, a short song with a strong beat. The 4K chart on Easy has only 180 notes.

Having selected a song, you're presented with some options.

This bit is crucial. The default speed setting is 4.0x. At this relatively slow speed, it is easy to see notes coming, but I find this makes me press the keys slower, and my timing fluctuates as a result. Bumping the speed up to 5.00x made my key presses more accurate and reliable.

If the notes aren't hitting the line in sync with the music, you can adjust Location. Location + shifts the notes downwards, making them hit earlier. Location - shifts the notes upwards, making them hit later. Judgement shifts the timing window earlier or later without altering the position of the notes on screen. While Location is useful for eliminating lag, I do not think there is any mileage in playing around with the Judgement setting. I found that altering the speed was enough to make everything click into place for me. Everybody's different, though, so experiment until you find the settings that work for you.

Now is your time to shine. Having calibrated your game correctly, you should be reliably hitting the notes within the required timing window. If you're still getting a lot of blue EXACTs, you may need to go back and change the game speed or the timing settings. Sometimes taking a break can help. I find I play at my best after I have warmed up on two or three songs, but if I have been playing for too long, I start making mistakes. So take those breaks!

Take heart: you have a small safety net. On the song Gameboy, you can get away with one blue EXACT and still get the 122% sync required for the achievement, so keep calm and feel the beat of the song, letting the music flow through your fingers.