Having issues with LtRt downmix

[teklife]

I'm currently downmixing a documentary from 5.1 to LtRt using Neyrinck SoundCode with the PL2 Encoder. (I haven't done this encoding myself before)

The downmix sounds good but I'm not so happy with the decoded 5.1 version.

When decoded, pretty much all the channels are all smeared together a bit. Music is bleeding into the centre from the L and R. Dialog and Narration are bleeding into the LR a bit, and it sounds phasey.

I don't know if this is pretty standard for decoded LtRt or if I'm messing something up.

If not, are there some ways to improve the decoded outcome?

[neilwilkes]

Matrixed surround is always a compromise, and you will never get an Lt/Rt downmix to sound as good as the original 5.1 discrete mix when run through anything, and with DPL II your settings are critical to standing a chance.
Can you please tell me what your DPL II settings are?

[Cheesehead]

LtRt should be retired IMHO.
It was a technology for a time when bandwidth wasn't available/ allotted for discreet surround channels.
Not only is the decoded signal often unsatisfying in surround, but it also to my ears makes the encoded stereo version lack definition.
It was great and clever for its time.

I don't see it being asked for so much on deliverables any more thankfully.
I hope it will gradually disappear.

[TVPostSound]

Originally Posted by Cheesehead

LtRt should be retired IMHO.
It was a technology for a time when bandwidth wasn't available/ allotted for discreet surround channels.
Not only is the decoded signal often unsatisfying in surround, but it also to my ears makes the encoded stereo version lack definition.
It was great and clever for its time.

I don't see it being asked for so much on deliverables any more thankfully.
I hope it will gradually disappear.

No one is asking for LTRT anymore.
Im down mixing LoRo for the 2 channel mix.

[spoons]

Originally Posted by TVPostSound

No one is asking for LTRT anymore.

Im down mixing LoRo for the 2 channel mix.

Just starting a series for Disney Channel. The abc cable networks spec they sent me still has a LtRt as the 2 channel mix needed along with the 5.1. I queried it but they said it’s required.
Thinking of using the Atmos production suite to make them but there’s no way of listening back to check it.



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[yanos]

Originally Posted by spoons

Just starting a series for Disney Channel. The abc cable networks spec they sent me still has a LtRt as the 2 channel mix needed along with the 5.1. I queried it but they said it’s required.

I was about to write more or less exactly the same thing.

[teklife]

Originally Posted by neilwilkes

Matrixed surround is always a compromise, and you will never get an Lt/Rt downmix to sound as good as the original 5.1 discrete mix when run through anything, and with DPL II your settings are critical to standing a chance.
Can you please tell me what your DPL II settings are?

Ok, thanks for clarifying that. I've since turned down the LSRS in Neyrinck which seems to be helping, The current settings I'm using are:

LR=0 C=-3 LSRS=-6 LFE=-3

[neilwilkes]

Originally Posted by teklife

Ok, thanks for clarifying that. I've since turned down the LSRS in Neyrinck which seems to be helping, The current settings I'm using are:

LR=0 C=-3 LSRS=-6 LFE=-3

The thing to always bear in mind is that this will always be a compromise. Whilst there is an amount of wishful thinking that it is no longer required, this is not yet the case. Although it is indeed true that the 5.1 specs for HDTV are Dolby Digital, which is discrete (as far as it goes, anyway) plus has it's own downmix metadata it is still a good idea to know how to do this "old school" as only last year I was asked to supply a 5.1 & an LtRt - on DTRS of all things!!

Your settings are very similar to the default setup in a Dolby Digital encoder so should be an acceptable starting point but the only way to know you have it right for your mix is to constantly check, check, check. It's a double compromise too as you first have to compromise your 5.1 mix to a Matrixed Lt/Rt stream & check the decoded version in 5.1 (and this is hard enough) but you also have to compromise your stereo - and for me this was always the biggest problem as it is a serious compromise and a dedicated stereo mix will always sound better (at least to my ears it does).

I can highly recommend the RPGA Surround document as a good start point.

[spoons]

Genuine question. Who’s actually listening to the LtRt decoded ?
I assume the HD broadcast uses my 5.1 discrete mix and a stereo mixdown for anyone listening in stereo.
Am I right in saying my LtRt will only be listened to decoded by someone who has a pro-logic system and is listening to the SD broadcast ?


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[neilwilkes]

Originally Posted by spoons

Genuine question. Who’s actually listening to the LtRt decoded ?
I assume the HD broadcast uses my 5.1 discrete mix and a stereo mixdown for anyone listening in stereo.
Am I right in saying my LtRt will only be listened to decoded by someone who has a pro-logic system and is listening to the SD broadcast ?

Sadly more common than you might think.
With TV the "standard" for HDTV is AC3 but again if the system is set up to defaults it will be stereo, meaning LtRt at best as things like the Sky HD Q box are never set to Dolby Digital by default, but stereo only as most people hook up the TV box straight to the TV via an HDMI line which out of the box is always, always set to stereo (the idea supposedly being setups are defaulted to get sound & picture up for as wide a range of hardware options as possible in order to allow the user to set it up properly from there).
Unless things have been set up by the end user to discrete 5.1, it will be an upmix or an LtRt, depending on the source.

It's even more complicated with optical discs - I still have in my emails a support request we got asking why the user was not getting the 5.1 output promised on the disc. A few questions asked revealed he did have a 5.1 setup - sort of (Sub/Satellite system) but it was actually connected up with RCA type connectors - Red & White. In short, he had a stereo output connected to a sub satellite system and genuinely did not understand why this would not work. I kept the email as a reminder of what can go wrong, even when a customer pays the store for installation.

Regarding monitoring, I am not familiar with Neyrinck as they seem to only cater for Mac OS (I run a PC) but they seem to know what they are doing and are properly licensed too. For DPL II and other Dolby Matrix systems I use the Minnetonka Audio DPL II encoder/decoder plugin (as well as the standalone one) and usually render out the export in real time, tracking this straight back in to the project for comparative tests in both stereo & surround modes.
Matrix surround always has been and still is a compromise - there is simply no getting away from this. That said, AC3 also downmixes automatically so be careful with the metadata there or you can ruin your mix ever so easily - dialnorm must be set correctly for the content, and adding "production information" metadata can also bring the hammer down on your mixes as well. DTS-HD Master Audio also has the option to embed an LtRt in the stream, and this should always be used if only because someone playing a 5.1 mix - or trying to - on a stereo only system may well get just front left/right and nothing else even if a separate dedicated stereo mix has been supplied and if 2 streams are included, default to the stereo one on optical discs - just in case.