What Sensitivity Should I Use For My Digital Device?

There are two common options for digital device sensitivity in SoundCheck, Unity Digital or Unity Digital (AES 17).

The default SoundCheck option is Unity Digital, which sets the sensitivity to 1 FS/FS. This is used to express peak and RMS amplitude. When used to define peak amplitude the maximum values are +1 and -1 FS which correspond to the maximum positive and negative digital codes in a digital audio sample stream. 1 FS RMS or 0 dB re 1 FS correspond to the RMS amplitude of a square wave that reaches the maximum positive and negative digital codes. The maximum amplitude of a sine wave in this scheme is therefore .707 FS or -3.01 dB re 1 FS. This represents the maximum amplitude of a sine wave where the peak positive and negative deflections reach the maximum positive and negative digital code.

Unity Digital (AES 17) is based off the Audio Engineering Society standard method for digital audio. AES17 defines 1 FS as the RMS amplitude of a sine wave that reaches the maximum positive and negative digital codes in a sample stream. The AES17 definition of FS cannot be used to express peak signal amplitudes.

For a signal of a given amplitude, the AES17 and SoundCheck definition of FS differ by 3.01 dB.