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In Reply to: RE: Audibility of a 1 ms delay posted by David Aiken on January 04, 2009 at 14:18:15
With a subwoofer, typically located 8 to 12 feet away from your ears, the majority of bass energy that reaches your ears will bounce off one or more room surfaces first.
Most of the bass energy that reaches your ears IS ALREADY DELAYED by many milliseconds because of the time needed for reflections off walls, floor, and ceiling ... before reaching your ears.
Also, there is no test evidence that any human can hear a 3 millisecond delay, much less a 1 millisecond delay, in the subwoofer frequencies under 100Hz.
I'd say the use of a digital subwoofer parametric equalizer to eliminate 2 to 4 bass peaks of +3 to +6dB .... is FAR more important to the bassline than the added 1 millisecond delay (that could be immediately eliminated by moving the subwoofer 1 foot closer to one's ears).
The probability that a subwoofer is currently located in a position where a mere 1ms of additional delay makes the "time gap" between the subwoofer and main speakers audible ... seems like a low probability event.
Let's say a specific listener with really good hearing can hear a 5ms subwoofer-satellite speaker time delay.
For an additional 1ms delay to make an audible difference, his subwoofer would have to be located where it had at least a 4ms delay (which would need an additional 1ms delay to become audible) ... but had no more than a 5ms delay (which would already be audible).
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Richard BassNut Greene
"The Floyd R. Turbo of Bingham Farms Michigan"
Follow Ups:
I could swear he said the human ear/brain combo was capable of discrimination on the order of a few femtoseconds. Is that wrong???
The direct sound always arrives first and is always higher in level than the first reflections.
What you say about most bass being reflections and delayed is true of all frequencies, not just bass frequencies. That doesn't make the direct sound unimportant. Some parts of our perception are drawn from the direct sound and some from the reflected. The direct sound usually gives us our timing for a sound since it arrives first. Exceptions can occur when a later arrival is louder, which doesn't occur with individual reflections, or arrives after an exceptionally long delay which won't occur in a room. The fact that, in some cases, the reflected sound field can, in total, be louder than the direct sound is usually irrelevant in small room situations like ours because it simply isn't sufficiently louder than the direct sound for the direct sound to lose precedence and, in any case, the brain is taking information from individual reflections, especially the first ones which arrive as separate events with clear intervals between them.
And you said: "Also, there is no test evidence that any human can hear a 3 millisecond delay, much less a 1 millisecond delay, in the subwoofer frequencies under 100Hz."
That still misses my point. There can be other factors delaying the direct sound and they may not delay it enough to make the delay audible so we have an inaudible delay. Add another delay and you can end up with a total delay that is audible. An additional delay of 1 ms will, in the right circumstances, be enough to make the total delay audible so it is possible to notice the addition of a 1 ms delay. I never said it will happen every time but it can happen in some cases.
David Aiken
Such a large percentage of the bass energy under 80Hz. is reflected energy that it's almost irrelevant to discuss direct versus reflected sound at those frequencies.
If subwoofers are set up properly, placed near other speakeres and located approximately the same distance from one's ears, then adding a 1ms subwoofer timing delay by using a digital parametric EQ is very unlikely to be audible.
But if the subwoofers were located far behind the main speakers, perhaps in the room corners where they produce the most uneven frequency response possible in a rectangular room, then it's possible adding just 1ms additional delay could create an audible deterioration of the bass note quality. (Moving the subwoofers 1 foot closer to one's ears would regain 1ms.)
One could also buy an analog parametric equalizer, which is more expensive, and much harder to set precisely, compared with a digital parametric equalizer ... but an analog EQ would avoid the 1ms time delay caused by A to D to A processing.
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Richard BassNut Greene
"The Floyd R. Turbo of Bingham Farms Michigan"
It's always relevant to consider direct vs reflected sound because they contribute different things to our perceptions.
And you keep missing the point that it's not the delay added by a particular device but the total delay introduced at all stages that can be the critical factor.
End of discussion.
David Aiken
The point seems to be whether an added 1ms delay for subwoofer frequencies would be audible, and not sound right.
I say that's very unlikely to be audible.
You had no point, other than pontificating that 1ms of additional delay might be the 'straw that broke the audio system's back'.
The benefit to the bassline frequency response from parametric EQ is so much more audible than a 1ms time delay, that I can't understand your theoretical problem with a +1ms delay.
An analog EQ would avoid the 1ms delay.
Or use a digital EQ, and move the subwoofer 1 foot closer.
Ho hum
Case closed.
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Richard BassNut Greene
"The Floyd R. Turbo of Bingham Farms Michigan"
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