Film-Tech Forum ARCHIVE: L/R & Centre sound mix

This is topic L/R & Centre sound mix in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Matthew Taylor (Member # 2310) on 10-30-2005, 02:57 PM:

I've been setting up my CP-50 and have noticed that there's almost no dialogue crosstalk in the surround channel but considerably more in the L/R channel, although the bias is toward the centre.

Do sound mixes generally put a reasonable amount of dialogue in the L/R as well as the centre or should I be getting minimal dialogue in the L/R speakers?

Posted by Rick Long Jr (Member # 541) on 10-30-2005, 03:36 PM:

What model cat 150 do you have? Dolby level been set?

Posted by Matthew Taylor (Member # 2310) on 10-30-2005, 05:12 PM:

I have the cat 150b. The dolby level has been set - as I say, the surrounds are working very well with no crosstalk now.

Posted by Stephen Furley (Member # 1277) on 10-30-2005, 05:32 PM:

I have no way of knowing how the film you are listening to was mixed, but the matrix encoding/decoding process only gives a partial separation between the centre channel and the left/right channels. If set up correctly, it should give almost total separation between the centre and surround channels.

The dialogue you are hearing in the L amd R channels may be there because:

a) the track was mixed that way.

b) the decoder is faulty.

c) you are just hearing the normal crosstalk between the C and the L/R channels which is inherrent in this system.

Or some combination of the above.

Posted by Gordon McLeod (Member # 33) on 10-30-2005, 06:25 PM:

If memory serves the 150b was about 25-30db seperation between channels

Posted by Louis Bornwasser (Member # 3063) on 10-30-2005, 09:00 PM:

Gordon is correct. The later 150 cards had much improved steering. "Discrete" center only is on the later cards: d,e,f or maybe just e & f; the 150b was actually not very good in this regard. Remember the center channel actually doesn't exist in analogue; it is the sum of what is on left and right. The later cards supress the latent center on L/R. Louis

Posted by Marin Zorica (Member # 1716) on 11-01-2005, 12:07 AM:

Ok, if film have good sound mix, do we hear dialogue from left and right channels, or just from center?

We are talking about CP-50.

Posted by Steve Guttag (Member # 268) on 11-01-2005, 06:14 AM:

A Cat 150 (any generation) should have enough steering that the Left and Right channels do not have any pronounced center channel information in them. While you might be able to hear it with a monitor just selected to Left and/or Right, when all three are playing, the Center should be so predominate that one shouldn't perceive the other two channels playing.

There was one (silly, in my opinion) thing called "draped dialogue" where dialogue was indeed placed in all three channels with the center being predominate. I don't recall it being used with SVA prints since I don't think the decoder could pull it off...however it was done on 70mm mixes.

Early Dolby Stereo decoders as used in the CP100 and early CP50s prior to the Cat 150 would indeed have all three channels playing at all times. These systems used a Cat. 110 for the CP50 (my memory escapes me on the CP100 but I think it was the Cat 82...I do recall you could use the cards interchangably though the CP100 card was metal clad).

This card merely boosted the center channel for summed information and reduced the center channel for non-summed to form a primative steering that was not at all convincing.

As an option, the Cat 116 could be added to the CP50 to decode the surrounds. The Cat 116 was also used in the SA1 through the SA3 for the CP100...though the suffix of the card changed with the card cages as the delay was moved onto the card itself.

With the Cat150, all of this changed. There was true steering of the sound and the surround decoder was now attached to the card for a composite card that did it all. The Cat 146 portion of the Cat 150 performed the L, C, R decoding.

The later cards, Cat150E and Cat150F are certainly better decoders and provide better steering to the sound.

Posted by Matthew Taylor (Member # 2310) on 11-01-2005, 05:58 PM:

So could it be a bad cat 150 that's causing noticable sound on the L/R then (as my surround doesn't have any bleed-through)?

Posted by Richard Hamilton (Member # 321) on 11-01-2005, 06:17 PM:

Matthew,
Is the dialogue in the monitor, or is it very noticable in the theater. Are you being too picky and standing an inch from the Left and Right speaker, or can you actually tell from anywhere in the auditorium?

Rick

Posted by Gordon McLeod (Member # 33) on 11-02-2005, 01:13 AM:

steve said "There was one (silly, in my opinion) thing called "draped dialogue" where dialogue was indeed placed in all three channels with the center being predominate. I don't recall it being used with SVA prints since I don't think the decoder could pull it off...however it was done on 70mm mixes."
actually what they did was encode the dialogue with a 45 phase shift and the older decoders would smear it between the 3 stage channels

you are coorect the cp 100 was the pentoptical module cat 82 which was the same as a 110

Posted by Matthew Taylor (Member # 2310) on 11-02-2005, 02:14 PM:

Hi Richard,

It is hard not to be picky because it's in my small home theater. Although the focus is on the centre speaker, it's really noticable on the L/R - you don't have to be close to notice it.

Posted by Louis Bornwasser (Member # 3063) on 11-02-2005, 03:26 PM:

See if you can borrow a later model 150 card; pref an e or f or later model. As I said before, the B was not very good. Louis