The ReplayGain panel allows you to configure at what level ReplayGain is calculated and lets you configure various parameters used when synthesizing Sound Check from ReplayGain.
The default target level for Yate's ReplayGain processing is -18 LUFS (Loudness units relative to Full Scale). You can specify a different target level if you wish.
Sound Check values are calculated based on stored ReplayGain values. The Sound Check offset setting can be used to change the parameters used to produce the value. The offset, if an, is relative to the LUFS value used to produce the ReplayGain Track Gain and ReplayGain Track Peak items. While any reasonable LUFS value can be used as a baseline for loudness, it makes more sense if all your tracks are based on the same value. As mentioned above, Yate's default LUFS value used in the ReplayGain calculations is -18. iTunes supposedly uses -16 as its LUFS value when doing its calculations. You can leave the ReplayGain LUFS as -18 and specify a Sound Check offset of 2 if you wish the Sound Check settings to be based on -16.
You can elect to use the track or album ReplayGain values when calculating the Sound Check values. While typically the track values are used, it is a personal preference.
When calculating the Sound Check values you can also choose to ignore peak data. Some applications produce the Sound Check data with peak and some do not. Historically, Yate used the peak data.