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Old 27th June 2009, 01:06 AM   #1
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The skills of engineers and producers of multi-channel program appear to be about at the level of early "ping-pong" stereo, but even at its best, the limitations inherent in the technology itself preclude realization of the objective of moving a virtual performance into our listening spaces.

Whatever spatial cues are present in two-channel recordings do not rely upon sidewall reflections for their effective reproduction. To the extent that having them "enhances" the apparent source width, the effect is pleasant, but also deleterious to imaging and spectral quality.

Studies indicate that given the ability to adjust reflections to increase spaciousness, listeners will dial them to extremes far in excess of any natural occurrence, and call the result "Good," artificial and inaccurate as it may be. Think Bose 901.

In this sense, soundstage and imaging are somewhat mutually exclusive, and I believe Geddes in his Summa paper, and Toole in his new book outline the psychoacoustics well. Cue extraction shows potential for providing us with the best of both....
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Old 27th June 2009, 01:25 AM   #2
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What's "Cue extraction"?

Best, Markus
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Old 27th June 2009, 01:45 AM   #3
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Quote:
Originally posted by markus76
What's "Cue extraction"?
Ascertaining those soundfield cues which are responsible for the perception, isolate them, and manage them. Research indicates what cues relate to enhanced ASW, apparent source width, and suggests that LEV, listener envelopment, cannot be achieved in small spaces such as our listening rooms except via surrounds implementing the appropriate delays. Please read Toole's book; I can't reproduce the illustrations without violating copyright.

The alignment Earl recommends incorporates some of these teachings: minimize the early first ipsilateral (same side) reflection via constant directivity, and emphasize the later low IACC, interaural cross-correlation, contralateral one. The text and diagram in his Summa paper contrasts the behavior of omni vs. CD, and you'll also find the 22.5° rationale presented here:

http://www.gedlee.com/downloads/Cum%20laude.pdf
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Old 27th June 2009, 03:03 AM   #4
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Know LEV, ASW, etc. pp. Don't think that answered my question. What cues of a stereo recording do you want to extract and how do you want to manage them in a way that is true to the recording?

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Old 27th June 2009, 04:56 AM   #5
ScottG is offline ScottG  United States
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Quote:
Originally posted by ZilchLab
The skills of engineers and producers of multi-channel program appear to be about at the level of early "ping-pong" stereo, but even at its best, the limitations inherent in the technology itself preclude realization of the objective of moving a virtual performance into our listening spaces.

Whatever spatial cues are present in two-channel recordings do not rely upon sidewall reflections for their effective reproduction. To the extent that having them "enhances" the apparent source width, the effect is pleasant, but also deleterious to imaging and spectral quality.

Studies indicate that given the ability to adjust reflections to increase spaciousness, listeners will dial them to extremes far in excess of any natural occurrence, and call the result "Good," artificial and inaccurate as it may be. Think Bose 901.

In this sense, soundstage and imaging are somewhat mutually exclusive, and I believe Geddes in his Summa paper, and Toole in his new book outline the psychoacoustics well. Cue extraction shows potential for providing us with the best of both....

What you are discussing here is rather different then what I was.

Note that I'm not suggesting that you should increase *listener* room reflections in an attempt to achieve better soundstaging or imaging. (..that was more the adding "ambiance channels camp".) But I *would* suggest than an increase to listener room reflections *may* not be quite as harmful to either imaging or soundstaging as others would argue.

Soundstaging is not an artifact of the listener's room. It's an artifact of the venue where the recording takes place (or is processed). It is integral to the performance, both artistically and in respect to image localization and as such is not at all mutually exclusive to imaging.
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Old 27th June 2009, 05:08 AM   #6
ScottG is offline ScottG  United States
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Quote:
Originally posted by ZilchLab

Research indicates what cues relate to enhanced ASW, apparent source width, and suggests that LEV, listener envelopment, cannot be achieved in small spaces such as our listening rooms except via surrounds implementing the appropriate delays.

..and it's quite incorrect.

Anyone who has heard good stereo reproduction could tell you the same.

Listener envelopment *can*, and often is achieved via good *2* channel reproduction. It's part of the reason people pay so much money for audio equipment or spend so much time in forums like these (..trying to find a way to do it for less).
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Old 27th June 2009, 01:28 PM   #7
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You guys are mixing things up. LEV can't be achieved with 2 channel stereo. LEV is a property of a diffuse (not a property of acoustically small rooms!) soundfield >80ms. There's no way to recreate these properties with 2 speakers. ASW can be created with strong lateral reflections but you sacrifice localisation by doing so. Furthermore the increase in ASW is not controlled by the recording. It's a incalculable property of the speaker–room interaction. In the end it's like sounding a speaker because "I like it better". That's no longer accurate sound reproduction that is true to the original (the recording).

Extreme toe-in of speakers has nothing to do with LEV or ASW (indirectly it can). It introduces trading effects when the listener moves to the left or the the right. But this effect is too incalculable because trading is signal dependent. In addition I suspect thresholds vary a great deal from person to person too.

Best, Markus
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Old 27th June 2009, 01:47 PM   #8
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80mS = 12.5Hz = 27.4 meters (90 ft) A big room.
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Old 27th June 2009, 02:03 PM   #9
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Level would be too low and the soundfield won't be diffuse (isotropic and homogeneous). Furthermore you would perceive an envelopment that is a distinctive property of the listening space and not the recording.

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Old 27th June 2009, 02:57 PM   #10
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Well, imho, if the speakers fire straight out, you usually get a not very good stereo image... and you are way off axis for the tweeter (which on some speakers might be a design benefit?). So that brings us to some sort of triangulation set up. The next question is if you are on axis, or alternately the speakers cross in front or behind you. In my room you can choose to sit in all three positions if you wish... different presentation of the soundfield.

Sort of like being on tracks and you can roll toward or away from the stage... that's all.

The issue of off center line imaging for your friend(s) who are visiting is tougher.

We should consider the Beveridge setup and what the Ohm F speakers do about this. (Heresy, both).

As far as the room, I'd say that 99.9% of us are in extremely handicapped rooms - way way too small to do justice. But then there is the converse problem that of the speakers being way way too small to deal with a way way bigger room. So, that leaves us with absorbing and diffusing reflections, which is not the same at all as a much longer natural return time (absorbed or diffused or not). If you want to hear things to good advantage I am afraid you and I need to build or buy a room the size of a small barn, literally.

Pick your compromises, optimize as much as possible and then you have to live with it...

_-_-bear

PS. the last guy to do something genuinely interesting with stereo was probably Jimi Hendrix on Electric Ladyland...
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