Panning and perceived volume

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inverseroom
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Panning and perceived volume

Post by inverseroom » Thu Nov 03, 2005 5:18 pm

OK, sound experts, answer me this. When you're mixing have a track centered, it's coming in equal proportions out of each speaker, correct? If you pan, say, hard right, does the sound come out in the same overall amplitude out of the right speaker, or half the amplitude, or somewhere in between? Of course hard panning makes a sound "jump" out of the mix, but is this because the same amount of volume is emanating from a single space, or because the sound, now isolated, acts on your psychology to take on new prominence?

Furthermore, if there is in fact some kind of equation at work here, does it differ from board to board? Is this an element of what gives a board a particular "sound"?

Sorry about all the undoubtedly incorrect terminology...but I think you know what I mean.

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Post by soundguy » Thu Nov 03, 2005 6:04 pm

most common panner configurations cause a 3dB drop when in the center position versus the full left or right positions. When you are panned hard right, for instance, you are moving the signal but also making it louder by 3dB compared to its level panned center.

make sense?

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Post by inverseroom » Thu Nov 03, 2005 6:50 pm

Yeah, sure. But...you mean in one speaker? Like if you mute the left speaker and then move the pot from hard right to center, then there will be a 3db drop in overall volume? But if you have the left one on, then the loss will be made up there?

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Post by soundguy » Thu Nov 03, 2005 8:02 pm

yes, I mean in one channel.

if you have a console with metering you can see it in real action for yourself, put in a steady tone, pan hard right and set gain so the channel is reading +3. When you move the panner to the middle the channel should now be sitting at 0. As far as psychoacoustics go, I really dont have a straight answer for you there's probably an old aes paper on the subject though I bet from back in the day when they invented stereo and panning on consoles. I suppose there is some make up of that loss psychoacoustically between two channels and just the one. If you have some time, maybe check out the following comparison:

take two channels. Set one pannned at 12 o'clock then pan the other hard right. Set the middle channel to read 0dB and set the hard right channel to read -3dB. Turn off the left speaker. They should, in theory, sound to be at about the same level.

To get more to the root of your question I'd then plug in the speaker you shut off and compare the middle channel in both speakers at 0dB to now multing the hard right channel to a second channel hard left and setting them both at -3dB.

Im not sure what this would prove. Im having a hard time getting this one out of my head and onto the screen ccoherently at the moment.

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Post by s00p3rm4n » Thu Nov 03, 2005 10:02 pm

I also think the frequency range, transients, aspects of the sound have a lot to do with perceived volume too. I guess I'm weird - I tend to listen for the weird stuff that's hard-panned to one side, and it usually is quickest to pop out for me (maybe that's because it's been specifically mixed that way? I dunno).
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Post by Professor » Fri Nov 04, 2005 2:45 am

I'm going to have to go with the notion that when you pan signal hard left it is at 0dB in the left speaker, then as you pan through to center it is reduced to -3dB in the left, and then as you pan through to hard right it drops to negative infinity in the left. Now the drop from 0 to -3dB is a 50% reduction in the energy, but it seems that next drop from -3 to -infinity is a slightly bigger drop. So maybe that's why it really seems to stand out and move quickly to peg in that speaker. Of course, there is also the psychoacoustic difference between a phantom signal located between two speakers, and the sudden arrival at a "point source" pegged right smack in the middle of a particular speaker.
As for the effect when considering both speakers, well when you're panned to the center you have reduced the energy to each speaker by 50%, but 50% plus 50% equals 100% and so the signal at the center is the same strength as the hard-panned left or right signal. Between hard and center is where the signal is meant to evenly transition and maintain the balance for a smooth movement across the stereo field. It's basically a logarithmic cross fade calibrated from 0 to -3 to -infinity and inverted for the other side.

Oddly enough, I believe there are some old consoles (maybe British-made ones) which were calibrated to -6dB at the center. And I really want to say that there was a recent digital board which had the option(!) of setting to either -3 or -6 at the center. I can't remember who it was, maybe as mundane as the Mackie d8b or as esoteric as the Otari Advanta that never made it to market, or maybe I'm just really tired. Damnit now I'll have to look that up.

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Post by joeysimms » Fri Nov 04, 2005 9:27 am

There seems to be something in panning either hard l,r, or center that makes the speakers happier. like, a guitar panned 2 o'clock r is causing weird sort of undefined phasey mush? I'm not saying it IS, just saying i've been much happier using hard left, hard right, and center. it seems to project better.
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Post by NewYorkDave » Fri Nov 04, 2005 10:09 am

It's really not complicated.

We're sitting in a room, facing a spaced pair of speakers, and there's a signal coming out of one speaker. If we send the same signal to a second speaker, at exactly the same amplitude, we've doubled the power of that signal. It won't sound "twice as loud" to our ears but it will indeed sound louder.

We add a panning control to allow us to move the apparent location of the sound from one speaker to the other and all points in between. But if we want the volume level to remain the same as it travels back and forth, the sum of the powers from the two speakers must always equal 1. With the signal panned dead center, the output of each speaker must be attenuated to one half of the full power... in other words, -3dB.

The important thing to remember is that we're concerned with the addition of powers, not of voltages. The reason for this is because a reverberant field (which describes all real-life rooms to a greater or lesser extent) randomizes phase, and as a result the not-phase-correlated-but-otherwise-identical signals add according to power and not voltage. In a truly dead acoustical space, and with the phase of the signals perfectly correlated, it would be simple addition of voltage.

The reason some British consoles went with a greater "center attenuation" is because of the rise of nearfield monitoring in the '60s and '70s and the reduced (but not eliminated!) contribution of room acoustics. -4.5dB was chosen by some as a good compromise between the two theoretical cases.

In order to maintain constant power, a panpot must have an unusual taper. Here's an illustration of such, from way back in 1941!

Image

More info at http://www.widescreenmuseum.com/sound/Fantasound1.htm
Scroll down to "THE DIFFERENTIAL JUNCTION NETWORK." The physics haven't changed in 64 years.

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Post by I'm Painting Again » Fri Nov 04, 2005 10:21 am

joeysimms wrote:There seems to be something in panning either hard l,r, or center that makes the speakers happier. like, a guitar panned 2 o'clock r is causing weird sort of undefined phasey mush? I'm not saying it IS, just saying i've been much happier using hard left, hard right, and center. it seems to project better.
the pan pots and electronics are happier too at those settings from what I understand..its more of a "unity" spot for panners..

Is that right techies?

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Post by inverseroom » Fri Nov 04, 2005 11:21 am

NewYorkDave wrote:In order to maintain constant power, a panpot must have an unusual taper. Here's an illustration of such, from way back in 1941!

Image
:D :D :D :D

That's what i wanted to know!!!

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Post by Knights Who Say Neve » Fri Nov 04, 2005 1:21 pm

Threads like this are why I love the TOMB.

Sorry, off topic, but I had to say it. :D
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Post by snuffinthepunk » Fri Nov 04, 2005 5:28 pm

inverseroom wrote:
NewYorkDave wrote:In order to maintain constant power, a panpot must have an unusual taper. Here's an illustration of such, from way back in 1941!

Image
:D :D :D :D

That's what i wanted to know!!!
crazy...i had this picture in mind as I was reading the post. So I'll go on to assume that it has something to do with our logarithmic hearing curve. Pan something hard left, then slowly sweep it to the right and we hardly notice at all because the signal in the right is so low, but as it logarithmically gets louder to us that would explain why there is the abrupt shift in it's place. does that sound right?
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Post by Family Hoof » Sat Nov 05, 2005 10:21 pm

What the two Daves said is the way it is. The amount of center attenuation is called a mixer's "pan law". Different consoles and DAWs do it differently. I think there is one piece of software which has no center attenuation, whereas Logic Audio allows you to choose between two or three different pan laws.

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Post by jajjguy » Sun Nov 06, 2005 6:41 am

just to beat this thing into the ground...

if you double the sound energy present in a room, say by turning on two loudspeakers instead of one, the level goes up by 3dB.

sound level (in decibels) = 10*log(energy)

if the sound energy of a guitar rocking out full strength in the left speaker is, say, 10,000,000, and then you pump the same signal into the right speaker as well, the total sound energy is now 20,000,000. and the sound pressure level in decibels jumps from

10*log(10,000,000) = 70dB
to
10*log(20,000,000) = 73dB

voila. and that's why the center pan position generally compensates by reducing the level by 3dB.


Surely someone will ask what the units are of sound energy. This gets complicated. Sound energy is a matter of fluctuations in air pressure, which is measured in pascals. But the 10,000,000 number above is not 10,000,000 pascals. It's a ratio of the pressure in the room to a reference pressure of 20 micropascals, which is near the lower limit of our hearing sensitivity. So the 10,000,000 number actually means 10,000,000 times the reference pressure, or 200 pascals. (At this point, i've probably made an arithmetic mistake or two, so look it up yourself before using these numbers for your rocket science project.)

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Post by syrupcore » Sun Nov 06, 2005 10:56 pm

Knights Who Say Neve wrote:Threads like this are why I love the TOMB.

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