Are there any Amps with 5.1 AAC Decoding on the horizon?

Stone Free

Active Member
Are there any Amps with 5.1 AAC Decoding on the horizon for use with Freeview TVs such as the Panasonics which dont have 5.1 AAC decoding ability?
 

dante01

Distinguished Member
AAC 5.1 is a matrixed and not a discrete format. Just use Dolby Pro Logic II. You'd need a receiver that supports AAC not a receiver that can decode AAC 5.1. Just output 2 channel stereo from your Freeview TV and then use ProLogic II. A far as I'm aware, no broadcaster uses AAC 5.1 and it is only apparent on iTunes downloads?
 
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Stone Free

Active Member
AAC 5.1 is a matrixed and not a discrete format. Just use Dolby Pro Logic II. You'd need a receiver that supports AAC not a receiver that can decode AAC 5.1. Just output 2 channel stereo from your Freeview TV and then use ProLogic II. A far as I'm aware, no broadcaster uses AAC 5.1 and it is only apparent on iTunes downloads?
The BBC use it on their Freeview HD service.

Also I don't think it is a matrixed format. I have seen it on many AVC Movie trailers.
 

dante01

Distinguished Member
The BBC uses the HE-AAC/AAC audio codec present in current Freeview HD set top boxes for the audio output on its Freeview HD television transmissions. The choice of codec prevents the BBC from transmitting on Freeview HD in surround sound.

The BBC is required to provide an audio description service on BBC HD. Typically there are two to three programmes everyday which are audio described. In order to achieve this the HE-AAC/AAC audio codec is used for Freeview BBC HD. The main audio is coded as AAC-LC and only the audio description is encoded as HE-AAC. Only a single type of audio decoder can be working at any one time. So, the main audio and the audio description must use the same encoding family in order for them to be successfully combined together at the receiver. The current bitrates used for the AAC-LC audio are entirely commensurate with those that could have been used for a Dolby AC3 (Dolby Digital) solution.

HE-AAC isn't apparently being used to transmit AAC 5.1 via Freeview, it is being used for Audio Description on the BBC's HD Freeview channel.

Format such as Dolby AC-3 or DTS or to output multi-channel linear PCM. Earlier versions of the UK D Book were only able to recommend the presence of transcoding. But now that transcoding solutions are becoming available the UK is no different from all other European standards. No doubt receiver manufacturers are working hard to incorporate these into their products.

However to help manufacturers develop products sometimes it is necessary to mandate certain features only after a suitable period has elapsed after publication in the D Book. So transcoding will become mandatory in all product launched after April 2011. In the meantime some manufacturers have already shown the capability of uploading this into existing deployed designs.

The use of an HDMI interface provides manufacturers with a choice of transcoding to Dolby AC-3 or DTS or delivering multi-channel linear PCM. The use of a SPDIF interface requires a transcoding operation as it cannot support the bitrates required for multi-channel linear PCM but can support bitstream formats.

Version 6.2.1 of the D Book requires receivers to support both the AAC (including
HE-AAC) and Dolby EAC3 (Dolby Digital+) formats. It is possible that the EAC3 format may also provide a future means for delivering receiver mix audio description.

These things are never straight forward but I hope that this answers the questions and gives you a little insight into why such decisions are made.

Phil Layton is Project Manager Digital Service Development BBC Research & Development.

BBC - BBC Internet Blog: Questions around surround sound on Freeview HD


It is the responsibility of the STB and TV manufacturers to provide provision for transcoding when HE-AAC and AAC 5.1 is utilised . As it stands, AAC 5.1 is not a recognised broadcast standard for discrete 5.1, it is a consequence of having to use the HE-AAC codec for Freeview. Freeview boxes and tuners should transcode AAC to more standardised formats such as PCM and/or Dolby Digital 5.1.

If you've recently invested in a new Freeview HD telly or set-top box, you're probably enjoying the World Cup in high definition.

But while you may be getting HD pictures, you may not be getting Dolby Digital 5.1 surround sound.

Why? Because it transpires that not all the Freeview HD TVs and set-top boxes currently on sale are capable of transcoding the multichannel audio signal being broadcast by the BBC on its HD programmes.

It's all to do with the fact that the Beeb has to provide an audio description service on BBC HD, and to do this it has to use the AAC audio codec present in Freeview HD receivers, rather than Dolby Digital.

Hence the main audio is coded as AAC-LC and the audio description as HE-AAC, because the main audio soundtrack and the audio description must use the same encoding family, as explained in this BBC blog by Phil Layton, project manager Digital Service Development, BBC R&D.

So why does this matter? Well, put simply, not all current Freeview HD TVs and set-top boxes can transcode from the AAC format to Dolby Digital so that your current AV equipment will be able to understand it.

According to the Beeb, transcoding will only become mandatory in all Freeview HD products after April 2011, which means there may well be confusion for a while to come.

With that in mind, we've undertaken our own research to find out which Freeview HD products do transcode and output Dolby Digital 5.1 via a digital connection to a home cinema amp/receiver, and which do not, so here are the results:

Goodmans GDB300HD - no

Humax HD-FOX T2 - yes (with this software upgrade)

Icecrypt T2200 - no

Digital Stream DHR8202U - no

Panasonic TX-L37V20 TV - no

Panasonic TX-L37S20 TV - no

Panasonic TX-P46G20 - no

Philips DTR5520 - no

Philips HDT8520 - no

Linsar FHD1 - yes

LG 32LE7900 - yes

Panasonic TX-L32D25 - no

Panasonic TX-l32S20 - no

Samsung UE32C6000 - yes

Sharp LC-32DH510 - no

Sony KDL-32EX503 - yes

Sony KDL-32EX703 - yes

Sony KDL-46EX503 TV - yes

Sony KDL-37EX503 TV - yes

Sony KDL-46HX703 - yes

Toshiba 32RV753 - yes

Toshiba 32SL753 - yes
Samsung UE37C6505 TV - yes

LG 37LE5900 TV - yes

Thanks to professorhat for this exhaustive thread on our Forums in which he tests the Philips DTR8520 and finds it does not output 5.1 sound (among other problems).

If you've recently bought a Freeview HD TV or receiver and are having trouble getting it to output Dolby Digital, please let us know in the Comments box below. We'll add more products to our own list as soon as we test them.

http://www.whathifi.com/News/Problems-with-Dolby-Digital-51-surround-sound-on-Freeview-HD-the-facts/


You're not likely to see AV receivers with specific AAC 5.1 decoding abilities any time soon, not when the TV or your Freeview box should be doing the transcoding prior to outputting the audio.

Related topic:
http://www.avforums.com/forums/freeview/1253508-freeview-hd-5-1-dolby-digital-surround-4.html




Yes, you are correct and I apologise for jumping in with my comment about AAC 5.1 being a matrixed format ;)
 
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Stone Free

Active Member
You're not likely to see AV receivers with specific AAC 5.1 decoding abilities any time soon, not when the TV or your Freeview box should be doing the transcoding prior to outputting the audio.
Yes, but what about those poor buggers who buy this years Panasonic range that a) don't transcode it to Dolby Digital, and b) according to them have no intention of producing an update to enable this!
 

dante01

Distinguished Member
Yes, but what about those poor buggers who buy this years Panasonic range that a) don't transcode it to Dolby Digital, and b) according to them have no intention of producing an update to enable this!

Blame Freeview for allowing something to be used before it is standardised. The manufacturers are under no obligation to implement technology that isn't as yet an accepted standard. The codec isn't set to be standardised until at least April of next year and the BBC shouldn't have started to use it until the manufacturers and governing bodies had accepted it. It may even turn out that HE-AAC isn't used and another format may be adopted?
 

dorix

Standard Member
I have a Panasonic DMR-XW380 and have spoken to panasonic on several occasions and as far as I can make out, NONE of their TVs or recorders at present which have HD freeview tuners can output 5.1.sound but all of the equivelant Sony products can.
 

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