Decibels Full Scale. dBFS is often used for displaying the level when a signal is recorded by the sound card. The sound card must digitalize the signal, which means that the signal is represented as numbers. The maximum value of the scale is 0, which is the maximum amplitude for the A/D converter.
If the input signal is too high, the PC does not have any numbers left that can represent it (there is a limit in the number size) and the signal will be digitally clipped. Therefore, when recording a signal, make sure that the dBFS value is as high as possible, but not as high as 0, because that may give clipping of the recorded signal. For measurements –1 to – 6 dBFS is very good, but in most cases –20 dBFS or even lower will also give a good result.