Creating a center track on a LR CD?

[Anonymous067]

So I'm playing around with some SFX for the show I'm working on...trying to play with a THUNDER cue!

Now, I looked at the BINK AUDIO TEST CD to get the idea of how to do this, but I want to know how on track two they get the SURROUND and CENTER channels. IS center just a combination of L and R? How do they do surround?? on a LR track...I don't get it...

http://www.binkster.net/extras.shtml

 

[Stookeybrd]

Bink has an explanation of each track on his CD. Scroll further down the page to the "Using the Bink Audio Test CD" link and he explains everything you'd ever want to know.

Tracks 1-2: Track Identification. These tracks will help you confirm the correct Left and Right patching and routing through your system. Track 2 has (in order) Left only, then Right only, then both Left and Right together (Center), then Left and Right with inverted polarity (Surround.) If your system has a polarity problem somewhere between Left and Right then the "Center" sample will sound unlocalized or absent and the "Surround" sample will seem punchy and centered. In a mono PA "Surround" should disappear completely.

 

[Anonymous067]

Bink has an explanation of each track on his CD. Scroll further down the page to the "Using the Bink Audio Test CD" link and he explains everything you'd ever want to know.

So is it possible to get three channels into the sound board? One for L, one for R, and one for another mono send?

 

[Anonymous067]

Bink has an explanation of each track on his CD. Scroll further down the page to the "Using the Bink Audio Test CD" link and he explains everything you'd ever want to know.

And on the surround, is it inverted from the other? so L is inverted from R? or they're BOTH inverted? I don't have a high level of understanding of this stuff!

 

[gpforet]

What are you trying to accomplish?

The bink CD is a two track CD. When used as a testing device, the left and right outputs are meant to routed as needed to test and calibrate a system. The routing is left entirely up to you. Each track is described as to what it contains. He also indicated what you should be hearing and helps you troubleshoot by telling you what may be wrong when you hear certain things.

Surround systems are wired with all speakers in-phase. Effects can be produced by sending out-of-phase content to one or more speakers.
Should you have questioned about whether your system is in-phase or not, the bink CD can be used to help determine that.

And on the surround, is it inverted from the other? so L is inverted from R? or they're BOTH inverted? I don't have a high level of understanding of this stuff!

 

[mixmaster]

And on the surround, is it inverted from the other? so L is inverted from R? or they're BOTH inverted? I don't have a high level of understanding of this stuff!

I'm not familiar with that CD but I would infer that the inversion is left inverted with respect to right on the fourth of that track.
"stereo" tracks typically have some information that is discrete to one track or the other because instruments have been panned left or right. Think about a guitar panned hard left or a keyboard hard right. Sounds panned to the middle have similar amounts of information in both the L and R tracks. If you invert the polarity of one side of a stereo signal, then those center-panned tracks become 180 degrees out of phase with themselves and start canceling themselves out. In a perfect world, stuff would cancel completely. In our less than perfect world, small differences in the amount of signal in each track means the cancellation is less than perfect.

The track section 3 test for this by providing some sort of signal (maybe pure tone instead of music) that "should" sum together cohesively in the center. If you have a polarity problem in you system, you get an inversion and will lose that "center" information. I suspect the next section of the track purposely inverts left with respect to right, intentionally causing some form of cancellation to the "center" information. A polarity issue in your gear will correct this issue and bring that center information back. The last comment leads me to believe that the information has been recorded in such a way that is cancels perfectly if mixed perfectly in a mono system.

There is no third channel on the CD, when I use the term "center information" I'm simply referring to information (tones, sounds, music, instruments, whatever) that is present in both the left and right channels simultaneously. Enough combing of channels with inverted channels could leave you with a center-information-only channel I suppose, but I wouldn't want to have to think all those inversions though.

 

[jkowtko]

So is it possible to get three channels into the sound board? One for L, one for R, and one for another mono send?

From a two-track (stereo) CD, it is not. But from a multi-track DVD, or from a computer using an audio interface that supports more than two outputs, you can supply as many tracks as you want to the board, and using the board, route to whatever speakers are connected independently to the board.

If you're not familiar with what I'm saying then you will need a lengthy tutorial on bus routing. In short, though, you need to have separate signal paths from source to destination, which includes audio player (DVD or PC), sound mixer, amps and speakers.

 

[Anonymous067]

If you're not familiar with what I'm saying then you will need a lengthy tutorial on bus routing. In short, though, you need to have separate signal paths from source to destination, which includes audio player (DVD or PC), sound mixer, amps and speakers.

Yup. Been at this for years....thanks. :]

 

[museav]

It is possible to get multiple channels from two tracks as that's how surround sound encoding works. However, it requires the signal to be matrix encoded during recording and an additional device to decode the two encoded tracks to the constituent channels during playback.

In the case of the Bink CD, I think he is simply saying the the 'center' track is L+R or summed mono and the 'surround' is L-R or one channel with the other inverted in polarity. If you have a stereo or mono system and the speakers are in polarity then the 'center' track will sound centered and louder and the 'surround' track should be very unfocused or disappear. If one channel is out of polarity then the inverse happens with the 'center' track sounding vague or disappearing and the 'surround' track sounding strong and centered.

The L-R concept is actually a little trick to get cheap 'pseudo surround', you wire across left + and right + and the resulting signal is the difference between left and right. I've used it a couple of times, the first time they tried it they called me to say it was not working at all, but when I asked what source they were using it turned out to be a mono videotape so the left and right channel signals were the same, which meant there would indeed be no 'surround' signal. But with a stereo source it actually worked in creating a simulated surround signal.

 

[gpforet]

Agreed, but the OP question was directed at the Bing CD which has no encoding.

It is possible to get multiple channels from two tracks as that's how surround sound encoding works. However, it requires the signal to be matrix encoded during recording and an additional device to decode the two encoded tracks to the constituent channels during playback.

In the case of the Bink CD, I think he is simply saying the the 'center' track is L+R or summed mono and the 'surround' is L-R or one channel with the other inverted in polarity. If you have a stereo or mono system and the speakers are in polarity then the 'center' track will sound centered and louder and the 'surround' track should be very unfocused or disappear. If one channel is out of polarity then the inverse happens with the 'center' track sounding vague or disappearing and the 'surround' track sounding strong and centered.

The L-R concept is actually a little trick to get cheap 'pseudo surround', you wire across left + and right + and the resulting signal is the difference between left and right. I've used it a couple of times, the first time they tried it they called me to say it was not working at all, but when I asked what source they were using it turned out to be a mono videotape so the left and right channel signals were the same, which meant there would indeed be no 'surround' signal. But with a stereo source it actually worked in creating a simulated surround signal.

 

[jkowtko]

Doesn't the Bink CD do this just to check phase between L and R?

 

[Anonymous067]

Doesn't the Bink CD do this just to check phase between L and R?

No, I believe Bink labels it L, R, Center, Surround. To check surround speakers...I think? Otherwise wouldn't he label it "phase check"?

 

[museav]

No, I believe Bink labels it L, R, Center, Surround. To check surround speakers...I think? Otherwise wouldn't he label it "phase check"?

I was pointing out that you can get more than one audio channel on two tracks, however I was not saying that is what the Bink CD is apparently doing. Read the second paragraph of my 11/11 response and Stookeybrd's 11/1 response. From the "Using the Bink Audio Test CD" notes it appears that the test track being discussed is intended to be a simple left/right routing and polarity check.

It does seem a good time to highlight the difference between polarity and phase. Polarity is amplitude related, phase is time related. Inverting the polarity of a sine wave, that is flipping it around the time axis, appears to have the same effect as a 180 degree phase shift of that same sine wave, however the latter is obtained by moving the sine wave one half wavelength along the time axis. This becomes a critical difference when one is addressing anything other than a single frequency sine wave, in other words for just about any real world signal.

 

[Anonymous067]

I was pointing out that you can get more than one audio channel on two tracks, however I was not saying that is what the Bink CD is apparently doing. Read the second paragraph of my 11/11 response and Stookeybrd's 11/1 response. From the "Using the Bink Audio Test CD" notes it appears that the test track being discussed is intended to be a simple left/right routing and polarity check.

It does seem a good time to highlight the difference between polarity and phase. Polarity is amplitude related, phase is time related. Inverting the polarity of a sine wave, that is flipping it around the time axis, appears to have the same effect as a 180 degree phase shift of that same sine wave, however the latter is obtained by moving the sine wave one half wavelength along the time axis. This becomes a critical difference when one is addressing anything other than a single frequency sine wave, in other words for just about any real world signal.

Sorry........