HOW IT WORKS
Auto Gain works by adjusting the level of tracks in your library up or down to a standard volume level. This ensures all the files in your library are at the same volume level.
As part of the overview building process, Serato DJ software automatically calculates an Auto Gain value for each track. This value represents the gain adjustment required to match the perceived loudness of the track to a reference level. If the Use Auto Gain option is checked, each time a track containing Auto Gain data is loaded to a deck, the track gain knob will be set to a value that matches the level of audio in the track to the reference value selected from the drop down list to the right.
The drop down list allows you to select from 89dB (quieter) to 98dB (louder), however 92dB (default setting) is the recommend value.
To turn auto gain on in Scratch Live, go to the Playback page of the Setup screen and check the "Use Auto Gain" option. You can select your desired dB value from the dropdown box.
In Serato DJ, you can also find the "Use Auto Gain" option in the "DJ Preferences" page of the setup screen.
If you have manually adjusted the Track Gain knob at all, Alt + Click on the knob to reset to the saved Auto-Gain level.