I've seen a number of attempts to describe the pronunciation of Loch & Bach [as in the composer], all of which seem to end up as Lock & Back. I hope this clears the air:The “ch” is a voiceless velar fricative. An explanation of the voiceless velar fricative is found at wikipedia.com under Voiceless velar fricative.
An excellent pronunciation of “loch” can be found at forvo.com under /word/loch#en
The Scottish “ch” is pronounced in the same manner as Jews pronounce “lochaim” or “chala” [as in the bread]. Or as the Germans pronounce “Bach”.I.e. NOT as “lock” “kala” or Back”.