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Originally Posted by ekliptiko
But what does it do to the audio? How is it creating this faux soundstage?
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When soundwaves arrive at your ears they are slightly distorted by your body, head and your pinna. This distortion depends on the direction the sound is coming from and that's how you can distinguish whether a sound is above, below, in front or behind you. So a couple clever people measured this distortion (called the HRTF head-related transfer frequencies) by putting microphones in test subjects' ears and playing sound from speakers in various positions around the person.
Unfortunately our bodies are all slightly different, so the HRTF differ from person to person, so Dolby had to come up with a compromise that worked reasonably well for most people.
Apart from HRTF, Dolby Headphones seems to add some reverberation, phase shift and crossfeed, essentially all the ingredients needed to simulate what you'd hear if the sound didn't come from headphones but from speakers in a virtual room.
Quote:
Originally Posted by ekliptiko
And does it degrade the audio? To what Extent?
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Yes, every bit of processing degrades the audio in some sense. However, there is a good reason why somebody might still want to enable Dolby Headphone, see below.
Quote:
Originally Posted by ekliptiko
IMO, some songs sound better with it on, and some not.
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Exactly. Some engineers master sound with headphones in mind, i.e. the audio has less stereo separation, more reverb and perhaps even HRTFs built in. If that's the case, you definitely want to listen with Dolby Headphone turned off.
However, other tracks are mastered strictly for stereo speakers. In that case if you just listen to the raw audio it can sound downright unpleasant with the voices seemingly in your head and one of your ears feeling deaf at times. A good example would be the 2009 Beatles Stereo Box Set.
There are some ways to get HRTF with higher fidelity than Dolby Headphone. For example I use Panorama 5 - a VST plugin that allows you to select from several different sets of HRTFs. That still not as good as going to a laboratory that can measure your actual individual HRTFs, but at least for me it's a big step up over the generic ones from Dolby. Also Panorama calculates sound reflections in the room (and applies HRTF to them as well) while Dolby only adds Reverb.
