Listen shenan1982 you cheeky little monkey why don't you think before you go posting stuff on line:
What I said is that there are different profiles, BT profiles, that IOS can use to do different things and even those profiles e.g. A2DP can use different codecs. IOS determines what BT profiles it uses and here IOS is clearly using a profile that is different from the one it uses to stream music A2DP. Perhaps it's using the Headset Profile (HSP) that is a low bitrate profile.
As others have noted when music is playing the Siri Voice is in high quality so perhaps this somehow tricks BT into using a different codec or profile. The Maps voice appears to be in high quality. And FaceTime is also not being implemented correctly too.
My point is you don't pick and chose haha