> With the spatial audio they're actually cheap if you figure I'm done with any Dolby Atmos, 9.1, 7.1, 5.1 etc stand alone setup. I'm watching movies with this.
Spatial audio is a replacement of true surround sound to you? it's a gimmicky weird audio effect to me. Zero sense of sound source behind or in front of me.
Humans have limited ability to discriminate between directly in front and directly in back based solely on cues encoded in the audio. It is a well-known ambiguity in how we hear space along that narrow axis. How you arrange the sound sources doesn't matter much. Research has demonstrated that human perception of a sound being "front" or "back" is determined by non-aural sensory cues. Specifically, if you can see a plausible sound source in front of you, you will hear it in front of you. Front-to-back spatial discrimination is based almost entirely on the visual cortex providing a model of the space in which the sound notionally exists.
In practice, humans subconsciously compensate for ambiguous front/back spatial positioning by turning their heads, putting the sound source on an axis where they do have excellent spatial discrimination. For obvious reasons this doesn't work well for headphones. Unless, of course, you have some kind of head tracking built into them.
I'm sure visual sensory input factors somewhat into how audio positioning is being processed by the human brain.
However an audio experience w/o visual input via physical surround sound sources provides convincing and precise positioning of audio sources. So that indicates visual input is just a tiny factor.
What I struggle with given all audio enters the two years, regardless of headphones or multiple speakers, why is the latter so much better at conveying "surround" sound than headphone? Does this distill down to a simple scenario of sound waves entering the two ears?
A lot of this research was done at NASA Ames in Mountain View. That's how I became familiar with it, I met some of the people working on it (a very long time ago). They had a lab where you could sit at the center of a sphere of speakers where they ran experiments on spatial perception of audio. It was really interesting. Broadly speaking, headphones should outperform surround speakers for spatial perception in absolute terms but it is much easier to generate quality spatial perception with cheap speakers than cheap headphones because of how it interacts with biology (see below).
In short, two "microphones" (your ears) is not enough to place a sound in 3-space, which makes audio illusions and perception gaps possible. Beyond time-of-flight and amplitude differentials, the human ear acts like a notch filter where the notch frequency changes as a function of angle of incidence. We don't hear the notch but the brain uses it to infer angle in a plane. This has significant issues e.g. it doesn't work well for new sounds with novel spectral signatures because we can't discriminate between a natural notch frequency and one created by the ear. It is possible to synthesize audio that breaks this part of our brain by synthesizing a set of cues that violate the laws of nature -- it is pretty uncomfortable. Creating spatial perception through signal processing has a couple limitations:
First, every human ear has a unique notch filter pattern. Spatial audio over headphones, which partially bypass the notch filtering, works best when they literally insert a microphone into your ear canal and measure the unique notch filtering patterns using test patterns. This can be fed into the software algorithms to create more accurate spatial cues for your unique ears. The perceived result is qualitatively different. There is no universal algorithm that works for everyone.
Second, the relationship between your ears and the sound sources don't change with headphones. In nature, animals either change the orientation of their ears, to basically sweep the notch frequency cues (humans have vestigial biology for this) or in the case of humans we move our heads for both notch frequency and time-of-flight cues. With headphones, the sound sources turn with you, so it produces no cues.
To make natural sounding spatial audio work on headphones, the audio source needs to be able to detect changes in head orientation in real-time and apply appropriate DSP to the raw audio. This is less of a problem with surround sound speaker systems because head motion provides these spatial cues naturally. I haven't tried it out but Apple's real-time head tracking plausibly provides the necessary DSP inputs to produce a spatial model that tracks as good or better than external speakers. Where external speakers fall short is that, unless you are in a carefully acoustically treated space, the space itself injects all kinds of spectral, temporal, and amplitude artifacts that unpredictably degrade the spatial cues in the audio.
>. I haven't tried it out but Apple's real-time head tracking plausibly provides the necessary DSP inputs to produce a spatial model that tracks as good or better than external speakers.
Apple's spatial audio head tracking is unreliable at best. I can fool the system easily by rotating my head at a speed that is slower than a snap rotation, side to side.
Even when the tracking is working properly, it sounds like simulated surround sound from home theater receivers of 20 yr sago.
> It is possible to synthesize audio that breaks this part of our brain by synthesizing a set of cues that violate the laws of nature -- it is pretty uncomfortable
Do you need special equipment to do it, or can it be done on a PC with speakers? I'd be quite interested in listening to this
Yeah I'm skeptical about the statement as well. If you used a good binaural microphone [1] to record someone talking in front of the dummy head, and behind, in a small room, then played the audio back to someone through decent headphones, I'd be tremendously surprised if they couldn't immediately discern which recording was which.
I own binaural recording equipment. My experience along with listening the golden standard of binaural recording (the barber shop simulation) indicates front and rear positioning is still not possible with binaural.
The left/right sound stage is huge though in binaural recordings!
Spatial audio is a replacement of true surround sound to you? it's a gimmicky weird audio effect to me. Zero sense of sound source behind or in front of me.