If you’ve ever taken lessons in a second language you will have come across recordings of native speakers. Normally there’s a short conversation and you’re supposed to be able to either translate it or hear words you’ve just learnt in context.
If you’re employed doing these recordings, I implore you: slow down. The people listening can’t speak the language yet, let alone at full speed while they’re trying to translate words in their head.
Half speed lets people hear words they haven’t learnt yet being pronounced slowly and correctly. It also lets them pick the words they know, translate them if required and put them into context of the conversation.
I’m not a bad student. My French is coming along in leaps and bounds. I can have conversations with my natively speaking mum about everyday things and I rarely miss a beat.
But with professionally recorded French language resources, they may as well be saying
« c’estunegrandpapillonblancsurlavoiturenoire »
Va lentement s’il vous plaît.