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Comment by devindotcom | Hacker News Reader

I don't mean to question your experience, but the inside/outside thing can very easily be a property of the headphones, not the mix. Certainly mixing it to emphasize that is a choice, but a good stereo mix is really not so fundamentally limited in its soundstage.

It may be the producer's deliberate choice to have the voice here, the guitar there, etc, and automatic "spatializers" may moot that choice. But of course so may playing it via a single-channel Bluetooth speaker. It's up to the listener to provide the experience they like best, but I question the need to have Apple pushing this particular type of mix so hard.

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> the inside/outside thing can very easily be a property of the headphones, not the mix

Not in any of my experience or knowledge. Literally every set of headphones makes it sound like both mono and stereo audio are coming from inside your head, unless the actual mastering is meant to provide an "outside your head" experience.

Originally, the "outside your head" experience only came from binaural recordings, where two microphones were placed inside dummy ears on a dummy head. That led to the famous "virtual barbershop" audio track and similar. The "outside" effect comes from a combination of relative delays* and the head-related transfer function (HRTF) [1] -- how the shape of your head and ear affects the sound waves.

Regular stereo mastering never uses any of these binaural effects, so it always sounds "inside", or "between the ears".

Spatializing stereo, on the other hand, is Apple's (quite successful) attempt to create relative delays and the HRTF. It has nothing to do with the quality or specifications of your headphones, and rather everything to do with the audio signal.

[1] https://en.wikipedia.org/wiki/Head-related_transfer_function

*To be precisely accurate, I believe the delays are actually included as part of the overall HRTF.

I don't think this is correct. The headphones themselves certainly have an large effect on the size and quality of the soundstage. Obviously encoding binaural delay and other psychoacoustic features is important too. But Apple is far from the first to do this kind of precision stereo manipulation.

> The headphones themselves certainly have an large effect on the size and quality of the soundstage.

They don't, not on its size. I'm not sure what mechanism by which you think they would?

> But Apple is far from the first to do this kind of precision stereo manipulation.

Certainly not -- I never suggested they were.

I don't know what to tell you. I've tested dozens of pairs of headphones and some have a clearly, obviously larger soundstage than others, with the same exact inputs. Others have a more "inside" feel. I think we must simply be talking about different things, because what I'm describing is a commonly cited property in headphone reviews and discussions.

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