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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: Stereo vs. multichannel: what are your thoughts on this statement (inside). posted by carcass93 on June 24, 2010 at 12:14:29:
Hi
This is a subject (the stereo image) that I have been interested in for some time.
It seems to me that the issue has several layers, the first of which being how recordings are made vs how do we hear in X and Y planes.
Given there is little one can do about recordings unless you’re willing to work at that end, an examination of basic stereo is in order.
In a reflection free space, two nearly perfect speakers produce a very strong phantom image when both are driven with an identical signal, like the “floating in your head” image one has with headphones, the image instead floats in front of you. Caused by inter-aural crosstalk, there is also a maximum angle where one looses that ability so most speakers are at about 60-80 degrees front view.
When there are close reflections near the speakers, if they have re-radiation at the edges, if the spread the signal out in time, the ability to form a concrete phantom image is reduced or defeated.
This happens because the speaker and it’s surrounding area radiate clues as to it’s physical location. The mono image depends on NOT having clues from the speaker interfering or competing with it..
At the same time, the ability to make a stereo panorama is similarly harmed because the only image that can be recorded is the one extending between the two sources. While on can use “tricks” using the pinna response, these are still only tricks. It is commonly thought that reflected room sound adds realism, but in reality one is normally stuck with much more than is desirable for a good stereo image.
The popularity ot larger systems like electrostats, magneplanars and Horns is due in part to the fact that they have “directivity” in the form of a reduced radiation to the sides and produce a larger “direct field” in front where the direct sound is significantly louder than the reflected sound.
To the degree one can listen in the direct field, the better the stereo image and the measured response looks much like the speaker when listened to or measured outdoors or anechoic. Often less directional speakers like cones and domes measure better at a meter but might have a response more like + - 10 or 20 dB at the listening position (the latter representing a variance of 40dB or 10,000:1 in level).
So, with the speaker one has room interaction, it’s ability to actually reproduce the signal with minimal spreading in time and it’s ability to radiate sound without or minimal a spatial signature that says “here I am” to your ears..
One can tell when a speaker has little signature if you play one by itself playing a voice etc. It is easy to tell what direction it is with your eyes closed but the less source signature it has, the harder it is to ‘hear” how far away it is, to localize it’s depth. That is because when you reduce the clues, all you have to go on is what is in the recording and it doesn’t include the speakers position.
The speakers I work on at work, these are for larger spaces than living rooms but the goals at least for sound quality are the same while the difficulties greater. As they became more like one acoustic source in time and space, I found it became much harder to tell the distance using my ears and the stereo image became much stronger, enough to work for a large audience.
All of this "floating in space" hinges on playing back something and here is where the chain is weakest because the item in question is a product intended to be liked.
Acoustically, it may not be obvious but even recording a real stereo image live is very hard.
As a result, only occasionally are recordings made where what you hear is what you would have heard live. Mostly, recordings are panned position mono sources which works pretty well because your ears primary detection is via loudness. A sense of space can be added with a wide variety of reverberations end so on. Each is a work of the producers art, played back in real time, assembled over weeks / months a sliver at a time.
Since most loudspeakers do not produce a strong enough center phantom image, a center channel (L&R summed) was the next step, with speakers that did produce a good phantom image, this allowed a wider angle for the L&R to be used. I think the next step was to add a L-r and R-l extraction which gave the difference information from each channel.
Anyway, we then went to the movie 5,7 etc formats and the rest is history sort of.
Back to the product, the point is much of today’s recorded product is intended to maximize the average playback system. Since so many loudspeakers are (imho) are lame excuses (sonically) for an accurate reproduction system, the recordings are best suited for those.
Is it any wonder the race has been to have smaller and smaller loudspeakers combined with the “loudest” recording possible (given the state of what is generally the weakest, most error filled link in any playback system the loudspeaker). The power of marketing and SAF sensitivity has killed dynamic range I suppose.
Anyway, I know others than myself are interested in “stereo”, as you say “looking through a window” like I said I am interested in this.
I have also been “fiddling around” with a microphone thing which captures a stereo image the way it seems to me that it should work. I have a music recording (some kids in an Irish folk group) which I will add shortly but if you’re interested in such things as window recordings, down load the Harley recording at the bottom of the page at the link. Leave it as a wave file (mp3 @320k conversion totally kills the fireworks), try it with headphones first, keep in mind, it is a very “quiet” sounding recording with a wide dynamic range, it has no compression or limiting and the bike is pretty loud.
I am planning to record the fireworks again this year with the latest 2ch version.
http://www.danleysoundlabs.com/technical%20downloads.html
Best,
Tom Danley
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Follow Ups
- RE: Stereo vs. multichannel: what are your thoughts on this statement (inside). - tomservo 09:25:35 06/25/10 (0)
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