DVD rotation speeds vary by type!


#1

I can acoustically hear differences in rotation speed at same data rate between:
-R/RW and +R/RW.
DVD SL and DVD-DL.
DVD+R DL has the highest rotation speed at same data rate.

DVD original and DVD-R,RW have identical rotation speeds.
DVD-DL and DVD-R DL have identical rotation speeds.

Tested with multiple disc drives (HL, TSST, Pionéer).

Is that deliberate? Why is that?