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 Forum index » How-tos » Ambiophonic Sound Reproduction
Ambiophonic shortcoming, or poor implementation?
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Adzic



Joined: Jan 22, 2020
Posts: 2
Location: France

PostPosted: Wed Jan 22, 2020 10:56 am    Post subject: Ambiophonic shortcoming, or poor implementation? Reply with quote  Mark this post and the followings unread

Hi!

I've been toying with ambiophonic for the last couple of days. I'm only on macOS so sadly I can't use AmbiophonicDSP, and I've only been able to explore it through the Aria3D extension (which doesn't offer detailed setting, but a few presets).

One thing I noticed, when closest to perfect cancellation I was able to get, is that the high frequencies information (up from 4-5Khz i'd say) don't seem to follow the rest of the spectrum in the imaging hologram.

The resulting sound is wide and quite exciting indeed, but the far left or right instruments seemed to be robbed from the top of their respective frequency range (as well as the very bottom, which is less problematic i.m.o.), which was only featured between the two speakers, and they ended up sounding a bit "veiled" or boxy.
This mid/high separation increased the contrast between the middle and side signal in a way that was a bit distracting, instead of having a full, united and coherent wall of sound.

Are those shortcomings intrinsic to the R.A.C.E technology (itself limited by laws of physics), or do they disappear with a closer-to-perfect cancellation?

I've read that upward from a certain point in the spectrum, the frequency waves-lengths get too short and random from proper cancellation, so this would point toward an inherent problem of 2-speakers ambiophonic system.

If this can't be overcome with the two-speaker ambiophony, does having a set of ambiphonic speakers behind, or a set of stereo speakers at 180 degrees on each side fixes that problem completely?

It would be a deciding factor for me, for if I'm to hear the violins at my 9 or 10 o clock, I do need the sheen of their bows to be coming from the same spot.

So if there are any expert present, I'd love your insight.
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Adzic



Joined: Jan 22, 2020
Posts: 2
Location: France

PostPosted: Thu Jan 23, 2020 6:34 am    Post subject: Reply with quote  Mark this post and the followings unread

So it seems true indeed, after some reading and testing, that what I'm describing is due to the immovable fact that frequencies, as they get higher, can't effectively be canceled.

So I'm not sure Ambiphonic sound reproduction is everything it claims to be:

It claims dramatically wider sound stage when it should claim the (impressive indeed) widening of the middle band only; since under 250Htz and above 5K it doesn't do much. The vast majority of instruments frequency range extends beyond 5K, and the timbre of side instruments is then denatured because divorced from an important part of their frequency range. Moreover, this widening is at the detriment of the perceived width of the high frequencies, which, being bound to stay within the limits of the physical speakers, collapse from 60 degrees in conventional equilateral stereo to 15-25 degrees.

This is made worse by the fact that a lot of mixing engineers are in the habit of hard panning (or close to hard panning) mostly the high-frequency sounds, for it doesn't affect the stable balance of the mix. So most often, hi-hats, shakers, tambourines, high synths, etc. are the widest elements of a mix, and designed to "frame" the rest of the stage by doing complimentary job from far left and far right, resulting in a pleasant wide (wide-ish, when you had a taste of ambiophony) symmetry.

In ambio, these elements are all but made mono and confined to 10-15 degrees from the center, while the mediums of pianos, guitars, synths, etc. are indeed dramatically wider —close to 180 degree—, resulting in a virtual stage that is quite far from the intended artistic purpose of the artists and engineers.

Here are a few examples in which this proves to be a distracting problem:

- The above-mentioned high-hats, shakers, etc. going from the intended extremes to the center of the stage.

- The broad-range instruments panned widely being divorced from a very important part of their timbre, the top end (which, if it is reproduced within the bound of the speakers, is too far apart from the perceived location of the instruments to be associated with it, —if it isn't drowned in the presence of the elements from the previous point). Ex: hard-panned guitar will be featured on the extrem, but missing their shiny strings sound, or pleasantly clicky plectrum strokes, which will be either heard towards the center or drowned in the activity there.

- In the context of orchestral music, which seems to be an important aim of the ambiophonic project, the medium band of the string section will increase in width thanks to the cancellation, while the top-end of their timbre will be collapsed and clumped together in the 20 degrees in front of you. This has negative implications in three different dimensions:


1) Timbre integrity: (see point above): everything that is outside of the 20 degrees covered by the speakers will lack to some degree part of its top-end.
1) Clarity: these high frequency are important in dissociating the lines during intricate counterpoint or more complex writing in general, and the top end of the cellos being smashed down in the center along with the top-end of the first violin (and everything in between), and competing now with the top end of the woodwinds, affects clarity a lot.
2) Proximity: The top-end of the spectrum is perhaps the most important cue concerning the proximity of the source. As sound travels in the air, higher frequencies will be increasingly absorbed first, and a lack of top-end is easily interpreted as increased distance from the listener, especially in an organic/acoustic context such as orchestral music. So the first violins (supposed to be closest to you) will appear through good cancellation to your 9 or 10 o'clock, let's say, but their top end is stuck in the middle, and too far from the perceived source (far left) to be associated and combined with it. The effective sound of the violin you hear to your left ends up sounding as if a mixing engineer dialed a low-pass at 5k, which makes it sound duller, further away and less intimate and immersive as a result. This also tends to squash a little the perception of depth of the room, for the "low passed" side strings will be imitating the natural low-pass created by the air absorption for the woodwinds, brass, and percussions, resulting in a shallower space.


- Lastly, in the context of a movie: I've tested a few minutes with a few scenes of Rogue One. The effect can be helpful and interesting in some regards, but at other times, it's far from ideal: there is a scene under the rain, in which the folleys artist hard-panned left and right the sound of the rain on stone (close to white noise). In stereo (especially with a headset, but even with speakers), it allows the immersive impression of the whole scene being "rained on", while still letting an invisible space for high frequencies in the middle for dialogues and other effects. In ambio, during the same scene, the rain is squashed in the 20 degrees between the speakers, being way less pleasant and immersive, and competing a little more with dialogues, and the drony ambiance that is extended out in the broadened stereo field is then divorced from the scene in a way that sounds more artificial.

I didn't have much time to test it, but I'm sure if I stumbled into that scenario in a few minutes, there are a lot of examples of that kind during movies and video games.


So, dear people of ambiophonic leniency, am I missing something there? I have to be, because when I read ambiophonics.org, I get the impression of someone very demanding and uncompromising on quality, and yet the things I describe above, while not disturbing to the highest degree in every scenario, are surely compromises of a nature I'm not willing to make, just to have an awesomely broader mid-band.

What do you think? [/list]
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