Oh, I didn’t know they exist. Have to take a look (or I’ve forgotten they do) … 
Otherwise there was almost all said about these chipmunk practices in these recent particular topics:
- Listening Practices Level 2 - what to aim for? - General / Questions - SSi Forum
- Double speed listening practice as described in Aran's recent videos - General / Questions - SSi Forum
- Listening practice too fast - General / Questions - SSi Forum
- Speed of listening exercises - General / Questions - SSi Forum
- New listening practices sound like Iestyn and Cat are underwater - General / Questions - SSi Forum
Here in the list are only the forum topics from this year and I hope it can bring some help and understanding of why and how.
Hwy!
Tatjana
EDIT to include @DaiRoberts’s own (I believe first on this forum) topic here
Shwmae Pawb