Final 35mm mix without Dolby encoding

[gato sapato]

Hello all,

What potential problems might I be running into if the final mix (for 35mm) I deliver to the lab is a simple 2-track, stereo .wav, without any kind of Dolby encoding (be it SR or SR-D) ?

Is there any encoding going on in labs, or any other process I should be aware of as the sound responsible ?

I´m worrying especially about compatibility with different decoding setups or settings across different cinemas. Does Dolby encoding, even the basic SR analogue Lt/Rt, guarantee a more reliable sound quality ?

[philper]

Originally Posted by gato sapato

Hello all,

What potential problems might I be running into if the final mix (for 35mm) I deliver to the lab is a simple 2-track, stereo .wav, without any kind of Dolby encoding (be it SR or SR-D) ?

Is there any encoding going on in labs, or any other process I should be aware of as the sound responsible ?

I´m worrying especially about compatibility with different decoding setups or settings across different cinemas. Does Dolby encoding, even the basic SR analogue Lt/Rt, guarantee a more reliable sound quality ?

I would let the people making the soundtrack master do the Dolby SR encoding, and yes it's a good idea. It doesn't matter to them whether you send stereo or LtRt.

Philip Perkins

[minister]

As Phil says, the Lab can (and should) do the SR. SR is simply the noise reduction for the optical track. SR•D is Dolby Digital 5.1 ... you are not doing that.

LtRt is something YOU create; a Lab does not make a LtRt mix.

If you haven't mixed it LtRt, I suggest you do. Plain stereo can have problems in a Dolby Equipped playback.

[philper]

Originally Posted by minister

As Phil says, the Lab can (and should) do the SR. SR is simply the noise reduction for the optical track. SR•D is Dolby Digital 5.1 ... you are not doing that.

LtRt is something YOU create; a Lab does not make a LtRt mix.

If you haven't mixed it LtRt, I suggest you do. Plain stereo can have problems in a Dolby Equipped playback.

But not the SR aspects of same. Absolutely true for a stereo track being run through a Dolby surround decoder (CP650 etc) though.

Philip Perkins

[gato sapato]

Thanks for the replies, I will do the Lt/Rt mix and hand it over to the lab.

Other than mixing and monitoring through Dolby equipment how can I make sure levels do not run too hot for the SR process at the lab? Is ther any kind of dynamics processing going on at the labs at this final stage ?

[soundboy]

Originally Posted by minister

As Phil says, the Lab can (and should) do the SR. SR is simply the noise reduction for the optical track. SR•D is Dolby Digital 5.1 ... you are not doing that.

LtRt is something YOU create; a Lab does not make a LtRt mix.

If you haven't mixed it LtRt, I suggest you do. Plain stereo can have problems in a Dolby Equipped playback.

According to his post he did a 2 channel stereo mix. Wouldn't it be an Lo Ro? He would need a 5.1 or 5.0, or 4.0 to matrix an Lt Rt. Right?
Oh, and to answer on levels, I think the DMU has a limiter to prevent excursions on the optical. If the mix is just overwhelmingly loud, (but why would it? you mixed on a calibrated stage didn't you?) the dolby tech will let you know.

[minister]

Originally Posted by soundboy

According to his post he did a 2 channel stereo mix. Wouldn't it be an Lo Ro? He would need a 5.1 or 5.0, or 4.0 to matrix an Lt Rt. Right?
Oh, and to answer on levels, I think the DMU has a limiter to prevent excursions on the optical. If the mix is just overwhelmingly loud, (but why would it? you mixed on a calibrated stage didn't you?) the dolby tech will let you know.

hey soundboy,
He did state at the outset that he had an LoRo. He asked if an LtRt guaranteed anything. I suggested he make one. You are quite right, it is a 5.1-->4-->2-->4 process.

Originally Posted by soundboy

Oh, and to answer on levels, I think the DMU has a limiter to prevent excursions on the optical. If the mix is just overwhelmingly loud, (but why would it? you mixed on a calibrated stage didn't you?) the dolby tech will let you know.

This is for a traditional Dolby PM. He is just sending it to the Lab. The lab encodes for SR only, no passing through the container in the DMU. No Dolby Tech.

[philper]

I think we (Minister and I) were suggesting that he send an LtRt INSTEAD of the LoRo to the lab if he suspects that the project will be played back through Dolby surround decoders. Even on very low budget films with limited theatrical showings and a short life in festivals this approach has worked better for me than LoRo.

Philip Perkins

[soundboy]

Ahh. I knew you both knew what you were talking about.
If you do, do a 5.1, know that it will be more work and more time.

[gato sapato]

I don´t yet have a final mix, and I still have the possibility of stereo, 4.0 and 5.1. All the surround elements would be ambience/atmospheres which I already had put aside for the possibility of a surround mix.

I guess the most logical thing in terms of sound quality would be to mix a 5.1 and from there take an Lt/Rt (with or without Dolby tech, that´s the question now, I´m based in Europe and I don´t know how Dolby procedures vary from what happens in the USA).

[Steven1145]

Lo/Ro, LtRt... I'd say it does'nt really matter, just as long as the OP monitors through an encode/decode monitoring chain. If you dont, you might be quite surprised to hear stuff going to the rear (out of phase content), or the music stuck in mono in the Centre (not enough difference between L and R in the music).
Also you absolutely need to bear in mind that 35mm optical does not have the same headroom as digital. At 140% optical modulation, the two optical analog waveforms touch, creating what is called crossmodulation distortion. If you mix too hot, this can totally ruin your mix (and have cost you an Optical Transfer for nothing). FYI 50% optical modulation is usually set at -20dBFS.
If your original 5.1 mix was done with a listening level of 85dB (C) per speaker, you should then the overall mix down by 3dB, and boost your monitors by 3dB. That's what happens in Dolby and DTS encoders: the 5.1 mix goes out of the console to the matrix encoder, the matrix encoder lowers the levels by 3dB and creates a LtRt which is then SR encoded.
On playback through a CP650 in the theatre, the analog playback is SR decoded, dematrixed and boosted by 3dB compared to the Digital track.

Best of luck.

[danijel]

Originally Posted by Steven1145

If your original 5.1 mix was done with a listening level of 85dB (C) per speaker, you should then the overall mix down by 3dB, and boost your monitors by 3dB. That's what happens in Dolby and DTS encoders: the 5.1 mix goes out of the console to the matrix encoder, the matrix encoder lowers the levels by 3dB and creates a LtRt which is then SR encoded.
On playback through a CP650 in the theatre, the analog playback is SR decoded, dematrixed and boosted by 3dB compared to the Digital track.

Sheesh, now you tell me that!!!

Thanks Steven, great info

[Steven1145]

Yes Danijel that's the sort of super-secret info we Dolby studios usually keep to ourselves to ensure that you come and mix at our place !

[philper]

Originally Posted by Steven1145

Lo/Ro, LtRt... I'd say it does'nt really matter, just as long as the OP monitors through an encode/decode monitoring chain. If you dont, you might be quite surprised to hear stuff going to the rear (out of phase content), or the music stuck in mono in the Centre (not enough difference between L and R in the music).
Also you absolutely need to bear in mind that 35mm optical does not have the same headroom as digital. At 140% optical modulation, the two optical analog waveforms touch, creating what is called crossmodulation distortion. If you mix too hot, this can totally ruin your mix (and have cost you an Optical Transfer for nothing). FYI 50% optical modulation is usually set at -20dBFS.
If your original 5.1 mix was done with a listening level of 85dB (C) per speaker, you should then the overall mix down by 3dB, and boost your monitors by 3dB. That's what happens in Dolby and DTS encoders: the 5.1 mix goes out of the console to the matrix encoder, the matrix encoder lowers the levels by 3dB and creates a LtRt which is then SR encoded.
On playback through a CP650 in the theatre, the analog playback is SR decoded, dematrixed and boosted by 3dB compared to the Digital track.

Best of luck.

This is all good advice, except that I have had LoRo mixes play fine through one Dolby system and Not Fine through others, esp in low budg situations. The safe thing to do is mix a 5.1 and then make a real LtRt w/ Dolby hardware or software--that mix will play w/o steering issues anywhere.

Philip Perkins