Music sounds sped up on iPhone 6S
Turns out, the 6S (and the 6S Plus) hardware sample rate cannot be changed when there's no headset or audio interface plugged into it. This means it''s stuck in the 48 kHz position. This is causing problems with many audio apps.
If you have this problem, try unplugging your headphones or audio cable and plug them back in again. That should reset the sample rate. It seems to only sound sped up when listening to music through the iPhone's speakers with nothing connected.
Hopefully Apple will release a fix soon but we are also trying to find a solution too.
Please let us know if you have any other issues at firstname.lastname@example.org