Question about attack speed with frenzy

Hello, was wondering how exactly IAS works with a skill like

Frenzy or

Double Swing.

Each attack animation is 2 swings, but does the main hand swing at a different speed then the offhand assuming 2 weapons with different speeds are equipped? Or does the game take some sort of average attack speed based on both weapons equipped and gives an equal animation time for each swing?

Cheers

According to the IAS calculator it only takes the Mainhand IAS and any Armor IAS into account. So mainhand (right) has to be rather fast, offhand can be anything.

https://d2.lc/IAS/

If remember it correct, the games takes the average of both weapons base speed and then add the IAS of the mainhand as weapon-IAS. IAS of the second weapon is ignored.