Rotel 7.1 MPEG Multichannel Decoder....any others?

[Disco Makberto]

Hello, e-Gang!

Okay, I have been doing some research in order to find a 7.1 MPEG Multichannel amplifier/receiver/decoder. Up to now, I have been able to find a few from Rotel, but just from Rotel. Do you know if there are any others from a different brand? I have found some non-Rotel 5.1 MPEG Multichannel decoders, but again, I am looking for a 7.1 MPEG Multichannel decoder. I have read that a 7.1 MPEG Multichannel decoder works in a similar way to a Dolby Prologic II in the sense that it upconverts a 5.1 signal to a 7.1 signal.

For the possible would-be trolls, I am not interested in discussing if Dolby or DTS is better than MPEG Multichannel or if MPEG multichannel is inferior or obsolete, etc. The point is that I want to try it, whether good or not-so-good, so that is why I am requesting helpful advice here.

Thank you cordially,

C Albert L
D-Mak

[guns1inger]

Dolby Pro-Logic II doesn't upmix 5.1 to 7.1upmixes stereo or matrixed Pro Logic to 5.1. Dolby 6.1 is EX, and DTS is ES.

Mpeg 2 audio 7.1 has discrete left and right centre channels in the mix. If they are not in the mix, then they aren't used. Any decoder that adds these will be on a brand by brand basis, as it isn't part of the mpeg-2 audio spec. Very few discs use multi-channel mpeg-2 audio, and only a handful use true 7.1, hence the sparse availability of mpeg-2 audio decoding amplifiers.

You might be interested in this http://home.online.no/~espen-b/mpeg/mpegdvd.pdf

A quick google indicates that while Onkyo, Harmon-Kardon and Kenwood, amongst others, speak of support for 7.1 channel mpeg audio, all of them do so by providing discrete 7.1 inputs for connecting a dedicated mpeg decoder that you have to supply.

[Disco Makberto]

Oopps, sorry about that, Guns1Inger! But I stand happily corrected. Let me see if I can find the link where the comparison is made:

"This format (MPEG Multichannel) is very similar to Dolby Prologic II but a specific part of the stream is dedicated to multichannel data". (From the Hypercube site).

So, is it correct to suppose that the similarity relies on its ability to upconverting? Otherwise, in what way they are similar?

Let me read your link.

Thank you. It is very interesting, though some points are beyong my comprehesion.

While we are at it, I remember having seen a drawing showing where the speakers would be located on a 5.1 and 7.1 MPEG multichannel set up, does anybody know if this is still available online?

Cheers,

C Albert L
D-Mak

P.S.: For some reason, the Hypercube site is down now.

[Disco Makberto]

Guns1Inger says:

"A quick google indicates that while Onkyo, Harmon-Kardon and Kenwood, amongst others, speak of support for 7.1 channel mpeg audio, all of them do so by providing discrete 7.1 inputs for connecting a dedicated mpeg decoder that you have to supply."

C Albert L responds:

I remember having read about the Onkyo, but I wasn't familiar about the others. Having to supply a dedicated MPEG decorder beats the purpose, I think. Conversely, if you read the manual for the Rotel RDV-1050, for instance, you will read:

"MPEG Multichannel. This feature expands the 5.1 channel audio format recorded on the disc to a 7.1 channel format".

If I undersand correctly, in regards to the Rotel RDV-1050, I would just need to input "raw" 5.1 MPEG Mutlichannel coming out of my DVD player into the amplifier. Towards this end, I believe that my Norcent DP-300 can output raw MPEG Multichannel. Then, this could be the way to go forward...

However, I still want to know about other options since the Rotel models are too expensive. Anyway, I think it's nice to know that the option to upconverting is viable albeit expensive.

C Albert L

[guns1inger]

If you player has 6 RCA outputs, then Onkyo, Kenwood etc all have high-end amps that can take the input. They do not decode mpeg-2 audio themselves, but then it also sounds like the Rotel doesn't, either. If some of them choose to create a pseudo set of centre right/left channels and that is important to you, that's a bonus. They will also do the same upmixing to centre left/right for AC3 5.1 and DTS. It's not an mpeg-2 specific trick. True mpeg-2 7.1 must be matrixed at the encoding stage, not the decoding stage. Also, there is a huge difference between adding a slight delay to fit two fake channels into a mix, that taking a stereo mix and building a pseudo 5.1 from it.

No-one of note bothers to author with multi-channel mpeg-2 audio. The few movies that have it are older titles from the beginning of DVD. It is demonstratively inferior to the alternatives, and thi sis why no-one bothers selling decoders. If you want it, then you need to get a player that decodes to 6 analogue outputs. According to the manual I downloaded for the Norcent DP-300, it does what most players do, which is downmix to a straight stereo PCM analogue output. This loses any multi-channel encoding that the original mpeg stream might have had. It's other option, also in common with most players, is to send the mpeg-2 audio stream out over the digital output, but then you need an amp that can do the decoding, which, as you are finding, is very difficult.

In short, mpeg-2 audio is an inferior surround encoding process that the consumer didn't need or want, and which is now supported purely as a legacy item. The world moved on, and has left it behind.

[Disco Makberto]

Hello, Guns1Inger!

I absolutely agree with you. The 7.1 MPEG Multichannel mix would be a pseudo 7.1 MPEG Multichannel mix, not a true 7.1 mix. However, unlike Dolby and others that can create true 7.1 at the disc level, in the case of MPEG Multichannel, the 7.1 mix is always created at the hardware level. In other words, all 7.1 MPEG Multichannel mix are pseudo 7.1 MPEG Multichannel mix because they are always created at the hardware level and not at the software or disc level. Let me see if I can find a link to support my claims:

From Answers.com:

"Technically there are software encoders around that can handle 5.1 but NOT 7.1. The MPEG Multichannel supports 7.1 which is created by players and setups which can decode an MPEG Multichannel bitstream from 5.1 and extract data from the matrix to form 7.1 pseudo-distrete channels of a 7.1 wide setup".

Now that I think about it, maybe that is why MPEG Multichannel 7.1 is someitmes compared to Dolby ProLogic II, namely the fat that both can create pseudo channels. I see a similiarity here; what do you say?

I certainly agree with you that MPEG Multichannel is a legacy technology, but I still want to try it. That doesn't mean that I will forget Dolby, for instance. I still like Dolby.

On side note related to sticking to old technology, I remember an old uncle-in-law I used to have. For some reason, he absolutely refused to use the Philips compact cassettes and only wanted to use the bulky 8-track cassettes. The stayed like this for many years. It was until I told him about the cassette to 8-track converter, and until I got him one, that he started to use compact cassettes.

In conclusion, Gus1Inger, assuming that I have a 5.1 Multichannel disc, and then I play it on my Norcent DP-300, and assuming that this is outputted in the "raw" via a digital output to the Roltek player, is it safe to say that it is possible to creat a pseudo 7.1 MPEG multichannel mix?

C Albert L
D-Mak

[guns1inger]

True mpeg surround audio is matrixed during the mix down and encoding stage, just like AC3 or DTS. That is, all the positioning information etc is stored in the stream. Dolby ProLogic is the same. True Dolby Prologic audio tracks have the positioning data matrixed in during encoding. They were more limited because they only had C/L/R and a mono rear pair. DPL II is more along the lines of pseudo 5.1 creation.

If you send AC3 5.1 (or 6.1 EX) or DTS through to your amp as a digital stream, it will decode it as AC3 or DTS. It won't convert it to mpeg audio, as there is nothing to be gained. You would have to send an mpeg audio digital stream though, which means a) you need a multi-channel mpeg audio source, and b) an amplifier that decodes digital mpeg audio streams or a player that decodes mpeg digital streams and outputs 6 - 8 analogue signals.

However the simplest way to confirm what the Rotel really does is to find a reseller and get a demo.

[Disco Makberto]

Yes, I mean to start with a 5.1 MPEG Multichannel disc (either true 5.1 mix or pseudo 5.1 mix but some form of MPEG Multichannel already on the disc), then use the Norcent DP-300 "raw" digital output (this "raw" stream is supposed to contain all 5.1 mulitchannel information) that will be connected to the digital input of the Roltek amplifier that, in turn, will create a pseudo 7.1 MPEG Multichannel. I think that my approach is correct, but of course, nothing is definite until undertaking real physical testing as you are correctly pointing out.

Keeping the same subject, my original request for help was to identify other amplifiers that can take a 5.1 MPEG Multichannel mix and upmix it to a pseudo 7.1 MPEG Multichannel, something like the Roltek is supposed to do. Anyway, remember that all 7.1 MPEG Multichannel devices only create a pseudo 7.1 mix, as far as I understand the issue, since this can only done at the hardware level (for there isn't any 7.1 MPEG Multichannel disc ever created).

If the Roltek cannot take the raw input, then I need to find an intermediate device that can take this raw signal from the Norcent and separate the raw signal into 6 channels as you told me. After that, I would just need to connect the 6 channels to the Roltek that, in turn, will create the pseudo 7.1 MPEG Multichannel.

Best,

C Albert L
D-Mak

[guns1inger]

You are completely missing the point the of the 7.1

If you feed the amp a 5.1 channel mix, all it is going to do is create the missing centre left and right channels. It is isn't going to create a 7.1 mix from scratch. Only if you have 8 speakers in your set up will you notice the difference, and all you will notice is audio from the two centre (l/R) speakers.

This one appears to take a digital mpeg audio stream. The manual for it states that "MPEG decoding is auto-detected and cannot be overridden", however you can force a 5.1 or 2 channel downmix. Up-mixing is basically done via DPL II.

http://www.rotel.com/content/manuals/rsp1068.pdf - page 28

[Disco Makberto]

Hey, Guns1Inger!

Of course, you are right, but I think I never said that I was going to use less than 8 speakers. It is understood that 8 speakers are needed, no problem with that. The missing channels are created phantomly; hence, the final mix is, of course, a pseudo mix, it is not a real mix. Again, as I said in the beginning, I know that some people have problems with pseudo mixes or they simply dislike them...good for them! In my case, I just want to try it, whether good or bad.

Yes, some Rotel models are supposed to be compatible, but unfortunately those are the only ones I have been able to find. In other words, I hope to find a similar model(s) but from a different manufacturer that is not Rotel.

Regards,

C Albert L