It's not even clear if there is some sort of soft clipping at play in Alexandre's case, but some of the Apple hardware has used such either in the CoreAudio driver or in the hardware codec itself. As I recall the main reasoning was to prevent hard clipping from damaging the tiny laptop speakers and some models it was bypassed when headphones are plugged in.

Personally, I test all mixes and masters in iTunes using the headphone out of a Mac Mini. If it sounds bad there I don't blame the driver though.

On Tue, Dec 31, 2013 at 8:00 PM, Simon Wise <simonzwise@gmail.com> wrote:

On 01/01/14 11:32, Chris Clepper wrote:

It's very, very easy to avoid any sort of clipping processing by using
hardware with drivers that don't have any! Avid, Apogee, MOTU, RME, and
many others have bit transparent OSX CoreAudio drivers.

Also, any DAC worth it's using can reconstruct far beyond 0dBFS without
distortion, so hearing volume increase past -1..1 in software is not
surprising. I recall the ADI 1955 and equivalent TI part putting out
+12dBFS or something ridiculous, but those ain't Wolfson low power
headphone codecs neither!

So it is the driver for the built-in audio output that is adding the feature/problem? I rarely use OSX these days, just an old setup with a G4 mac mini and a MOTU that hasn't been updated for years but still does its job nicely.

Simon