Audio: mixer track level different from bus1 level

Hello,

Could someone tell me why on the edit page, when I play audio on the timeline,
the audio level on bus1 is roughly 3db lower to that of the source track?

i.e. Source track peaks at -15db, bus1 peaks at -18db.

Track gain sliders are at 0.0.

Is this normal?

Thanks

The summation of two identical signals of equal amplitude and phase increases the level of the resulting signal, hence the attenuation on the stereo Bus 1 to produce equal power output and equal perceived loudness. This is the result of Pan Law, in this case “-3dB compensation” being applied.

Thanks Reynaud for the comprehensive answer.
I will spent the rest of the week digesting that.