Home |
Search |
Today's Posts |
#1
|
|||
|
|||
Another older article from Ferstler
I thought I would give you winners another article draft to
play around with. I published this one a number of years ago, and even had a somewhat different version as part of a chapter in my third book. To make it fit in with the group here and be a bit more up to date I have edited it slightly. Channel Balance and Channel Shifting. Just how much of a difference in LEVEL between two speakers of a stereo pair is needed to shift a centered "image" off to one side? If one sits some distance away but exactly on the axis between two speakers (in the so-called "sweet spot"), identical sounds coming from each system will form a centered, "phantom" image, provided the speakers are well positioned and working OK. If the sound of one channel is made just one dB louder in level than the other, there will be only a very slight change in the perceived location of the central image toward the louder speaker. One dB isn't very much, but it can move that central image a tad. If a 3-dB difference is produced, a definite shift will take place, however. If your speakers are about 12 feet apart and you are sitting on the central axis about 12 feet back from a line drawn between them, a difference of that magnitude will move the central sound about two feet closer to the louder unit. Under similar listening conditions, a 6-dB difference will move the central image to a point about mid way between center and the louder speaker. A 10-dB difference will move it to within a foot or two of the louder one. Finally, a 15-dB difference will result in a nearly complete collapse of the central image into the louder-playing system. If one sits off to the side a bit while this is going on, it will be possible to see how the balance control will help to keep the central image centered for the best sound under such conditions, by adjusting the relative levels of each channel. That control is a useful tool for musical enjoyment. Even if one's receiver or power amplifier has no level meters to verify such balance testing, adjusting the balance control while sitting in a variety of locations will be a good way to learn more about how to edit your system for good performance. Just remember to use a recording with a tightly focused central image, such as a solo singer. Test discs are excellent for this kind of thing, too. OK, going a bit further, just how much of a difference in TIME between the signals of both speakers is required to shift the image to one side? Well, during stereo playback, with the listener located in the sweet spot, all that is required to move a centralized image strongly toward either speaker is a delay or advance in the sound to one channel of 1 to 1.5 milliseconds. Sound moves at 1130 feet per second, so a distance difference of only 1.1 to 1.7 feet will achieve the 1 to 1.5 ms required. Even a difference of a bit less than .5 ms (under half a foot) will shift the image about 20 degrees off center. This is why shifting the listening position to one side a couple of feet will cause the sound to shift radically toward the nearer speaker. (Moving to one side also causes a small change in the relative sound levels of the two speakers but the main cause for the image shift is the timing change.) If a pair of speakers is 12-feet apart and the listener seated at a central position 12 feet from the axis between the speakers, the signal path from each speaker to the listener is about 13.5 feet. If the listener moves 2 feet to the left, the signal path from the left speaker drops to 12.6 feet and the one from the right speaker increases to 14.4 feet, a difference of 1.8 feet. This is sufficient to shift the sounds of transient signals radically to the left and will cause steady-state sounds to have a phasy and diffuse quality, because of comb-filtering effects. Correcting this can be partially accomplished by using the balance control to increase the gain in the more distant speaker by 6 to 10 dB. (Increasing its level by a 6 dB will have the effect of re-centering an image that was shifted sideways by a 1.25 millisecond time delay or a difference in distances to each speaker of 1.4 feet.) This will help transient signals stay properly positioned but will not eliminate the phasy quality of steady-state signals. When listening critically, there is no substitute for sitting in the sweet spot and keeping the balance control centered. Correcting the problem can be better accomplished by use of a center-channel speaker and properly adjusted center steering. Usually, if you engage your center channel when playing two-channel program material (via Dolby Pro Logic, DPL II, DTS Neo:6, or some other proprietary steering system that is closely related to DPL), there will be a general collapse toward the center that will ruin or at least partially ruin the sound-stage spread. Most two-channel music recordings are not happy with a properly set up Dolby or Dolby-like center-steering arrangement. However, if you back off the center level about -3 dB, the stage width will be nearly completely restored. The amount required may vary, and some recordings might require as much as a 6-dB cut in the center. In spite of this reduction in center level, the central focus should be better that it would be with a "phantom" center, not only when listening from off axis, but also from on axis. When sitting right in the middle, the simulated "hard" center somewhat eliminates the four-arrival-clue phenomenon that we get with a phantom center, and the result is a sense of solidity in the middle of the soundstage that we normally only experience when we listen to a real performer in that location. Needless to say, for the center channel to work to best effect, the center speaker itself has to be a good one (hopefully the equal of the left and right mains in terms of upper bass, midrange, and treble performance) and it also needs to be at a height that is similar to that of the main speakers. Unfortunately, this is not the case with a lot of home-theater systems. Channel Separation Typical CD players have an isolation level between channels of anywhere from 80 to 110 dB. (The hypothetical, 16-bit limit is about 96 dB.) Power amplifiers do nearly as well, sometimes also having in excess of 100 dB. I recently have reviewed one that was considerably better. When CD players are tested by some enthusiast magazines, the reviewers often discuss extremes of channel separation as if it makes a great deal of difference. Some get quite carried away and attribute tight imaging or an expansive sound stage to the very high separation measurements found on some super-grade (and super-expensive) models. (Still, remember that cheaper models often measure just as impressively.) However, for all intents and purposes, a channel separation of 30 dB is "perfect" (at least with musical program material) and it is nearly impossible to detect any benefit from separation levels in excess of even 20 dB. Look at it this way, a 10 dB difference in sound level is a power difference of 10 to 1. Twenty dB adds up to 100 to 1. That is, if one channel is putting out 1 watt and the other is 10 dB louder, the latter is generating 10 watts. If it is 20 dB up from the one-watt channel, it is generating 100 watts. Now, even a neophyte will realize that if one channel is delivering one watt to a speaker system and the other is cranking out a hundred times that amount, it will be impossible to hear what the weaker channel is playing - even if the listener is sitting nearly on top of the softer-playing speaker. A mere 20 dB of separation generates level differences so large that going beyond that point is academic. This is why typical phonograph cartridges, which rarely have much better than 20 to 25 dB of separation, are able to give us stereo. While players that cannot achieve separation levels of at least 80 dB may have analog-circuit design defects or a malfunction that precipitates other audible problems, people who place much importance on CD player channel separation that is notably better than that are sweating unimportant details. Howard Ferstler |
#2
|
|||
|
|||
"Howard Ferstler" wrote in message ... I thought garbage deleted Margaret |
#3
|
|||
|
|||
"Howard Ferstler" wrote in message ... I thought I would give you winners another article draft to play around with. I published this one a number of years ago, and even had a somewhat different version as part of a chapter in my third book. To make it fit in with the group here and be a bit more up to date I have edited it slightly. Channel Balance and Channel Shifting. [snip garbage] Sound moves at 1130 feet per second, so a distance difference of only 1.1 to 1.7 feet will achieve the 1 to 1.5 ms required. Even a difference of a bit less than .5 ms (under half a foot) will shift the image about 20 degrees off center. [above=utter garbage] Howard, a little reminder about the speed of sound. According to the ASTM, http://www.aerospaceweb.org/question...re/q0126.shtml, the speed of sound is defined as 1,116.4 feet/second, not 1130. This is why shifting the listening position to one side a couple of feet will cause the sound to shift radically toward the nearer speaker. No, it's not. You are incorrectly applying the theory of localization of impulse sounds to music. It doesn't work that way. (Moving to one side also causes a small change in the relative sound levels of the two speakers but the main cause for the image shift is the [more garbage snipped] Howard Ferstler Howard, you've filled your allotted garbage can for this week. Further dumps not permitted until next week's pickup. |
#4
|
|||
|
|||
Howard "Asperger" Ferstler said:
I thought I would give you winners another article draft to play around with. We didn't play around with the first one. We ignored it. Did you ignore the link I gave you for the information on Asperger's Syndrome? Unlike your articles, it is very useful, and might make your life a bit easier. Boon |
#5
|
|||
|
|||
Margaret von Busenhalter-Butt wrote:
"Howard Ferstler" wrote in message ... I thought garbage deleted Margaret As usual, my comments went right over your head. Grow a brain, Margaret. Howard Ferstler |
#6
|
|||
|
|||
Robert Morein wrote:
"Howard Ferstler" wrote in message ... I thought I would give you winners another article draft to play around with. I published this one a number of years ago, and even had a somewhat different version as part of a chapter in my third book. To make it fit in with the group here and be a bit more up to date I have edited it slightly. Channel Balance and Channel Shifting. [snip garbage] Sound moves at 1130 feet per second, so a distance difference of only 1.1 to 1.7 feet will achieve the 1 to 1.5 ms required. Even a difference of a bit less than .5 ms (under half a foot) will shift the image about 20 degrees off center. [above=utter garbage] Howard, a little reminder about the speed of sound. According to the ASTM, http://www.aerospaceweb.org/question...re/q0126.shtml, the speed of sound is defined as 1,116.4 feet/second, not 1130. At sea level. On average, 1130 fps works best, simply because most people do not live at sea level. The practical difference between the two numbers we have both noted, at least for use with consumer-related audio topics, is slight at best. This is why shifting the listening position to one side a couple of feet will cause the sound to shift radically toward the nearer speaker. No, it's not. You are incorrectly applying the theory of localization of impulse sounds to music. It doesn't work that way. Read the whole article. It deals with both time delays and level differences. Then, go sit in front of your speakers and do some listening. Get a good test disc to supply the signals. (Moving to one side also causes a small change in the relative sound levels of the two speakers but the main cause for the image shift is the [more garbage snipped] Howard, you've filled your allotted garbage can for this week. Further dumps not permitted until next week's pickup. At least I post sometimes lengthy material about audio, which is more than we can say about you backbiting nitwits. The best most of you can do is make inane suggestions about what products to buy. Howard Ferstler |
#7
|
|||
|
|||
Marc Phillips wrote:
Howard "Asperger" Ferstler said: I thought I would give you winners another article draft to play around with. We didn't play around with the first one. We ignored it. Over your head. One would think that if you REALLY want to prove that I am worthless as an audio writer you would read and dissect the articles and then show where I am wrong. However, you are simply unable to do this, because the material is over your head. Did you ignore the link I gave you for the information on Asperger's Syndrome? Unlike your articles, it is very useful, and might make your life a bit easier. This is an audio newsgroup. Why not read my material and show everyone just how wrong I am? Howard Ferstler |
#8
|
|||
|
|||
Howard said:
Marc Phillips wrote: Howard "Asperger" Ferstler said: I thought I would give you winners another article draft to play around with. We didn't play around with the first one. We ignored it. Over your head. Do you understand the word "ignore"? How can something be over your head if you ignore it? In order for something to be over one's head, they have to read it and THEN not understand it. Evidently the English language is over YOUR head. One would think that if you REALLY want to prove that I am worthless as an audio writer you would read and dissect the articles and then show where I am wrong. That would require giving you much more attention than you deserve, which is certainly your objective. However, you are simply unable to do this, because the material is over your head. See above concerning your inability to understand what other people write. Did you ignore the link I gave you for the information on Asperger's Syndrome? Unlike your articles, it is very useful, and might make your life a bit easier. This is an audio newsgroup. Why not read my material and show everyone just how wrong I am? Why not read the material I provided and see how right I am? Boon |
#9
|
|||
|
|||
On Tue, 05 Oct 2004 20:46:35 -0400, Howard Ferstler
wrote: At least I post sometimes lengthy material about audio, |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Article draft from Ferstler | Audio Opinions | |||
Ferstler Readies and Article | Audio Opinions | |||
[Admin] Rec.Audio.High-End Newsgroup Guidelines | High End Audio | |||
[Admin] Rec.Audio.High-End Newsgroup Guidelines | High End Audio | |||
[Admin] Rec.Audio.High-End Newsgroup Guidelines | High End Audio |