Which is true and contributes to the audio delay. But even on my 5S's own speaker or on wired headphones, there is a very noticeable delay when the audio circuit needs to wake up to play a UI sound. For example, entering my PIN or typing on the keyboard (I have the keyboard sound on). Once it's active it's fine, but there is definitely a startup delay in the circuits in the iPhone itself.
10/14/15 at 8:30pm