View Full Version : Dolby 5.1
Miracle Premium Twin HD - various VIX Apollo builds 030 to 39
When viewing a Freeview (UK Terrestrial) HD program with Dolby 5.1 audio what audio standard is output from the Micraclebox Premium Twin HD on the HDMI and on the S/PDIF (TOSlink) optical sockets.
I have an old (pre HDMI) Onkyo AV amplifier with only S/PDIF optical/coax digital inputs and can only get the Miraclebox to output audio if I set the AAC downmix to 'yes'. This doesn't give 5.1 over the S/PDIF (TOSlink) link which suggests that what is coming down the link is in a 2 channel PCM format.
If I could connect an AV amplifier via HDMI I would I get 5.1. via 5 channel PCM?
Or is the output format something else?
Some background for my conclusion (which may be incorrect) can be found in posts #5 and #16 from:
http://forums.digitalspy.co.uk/showthread.php?t=1761159
I also base my conclusions on the same AV amp being connected to 3 other sources of Dolby 5.1 which the AV amplifier correctly identifies as 5.1 because it is coming down the S/PDIF (TOSlink) links in a different format.
According to the linked thread Freeview HD is encoded in AAC, not Dolby Digital 5.1, so yes you would have to use AAC downmix. For sure, S/PDIF hardware limitations mean that it only supports 2 channels of uncompressed audio, so no way of getting a six channel PCM stream there.
Do you have any way of trying the equivalent channel on Freesat? On that platform there are occasional actual DD 5.1 programmes, which should be ok on S/PDIF as it supports compressed audio. You would have to ensure that DD downmix is off in that case.
HDMI will support six channels of uncompressed PCM audio, but I don't know if the MB Twin is capable of outputting multichannel PCM properly. There are settings on the menu, but I've tried six channel FLAC high-res audio and the MB (and the Quad Plus) struggle to handle any audio data with a sampling rate over 48kHz. What seems to happen in that case is that it tries to downsample everything to 48kHz and output as two channel over HDMI.
With a compressed AAC multichannel stream it MAY output this correctly as six channel PCM audio over HDMI, but I have no real way of testing this as I'm outside the UK Freeview transmission area.
Do you have any way of trying the equivalent channel on Freesat? On that platform there are occasional actual DD 5.1 programmes, which should be ok on S/PDIF as it supports compressed audio. You would have to ensure that DD downmix is off in that case.
I've only got (hybrid) terrestrial tuners in my Miraclebox but my Humax HD satellite box gives Dolby Digital 5.1 over S/PDIF.
HDMI will support six channels of uncompressed PCM audio, but I don't know if the MB Twin is capable of outputting multichannel PCM properly. There are settings on the menu,
The only menu settings on the VIX image seem to be to switch downmix on/off. I've found no other menu settings for audio with respect to HD terrestrial TV apart for finding the option of switching between the Audio Description (AD) channel and the real audio. I assume that the Miraclebox/VIX doesn't support mixing these two audio channels.
With a compressed AAC multichannel stream it MAY output this correctly as six channel PCM audio over HDMI, but I have no real way of testing this as I'm outside the UK Freeview transmission area.
Another Miraclebox user, on another forum, suggests that his AV box may be correctly decoding multi-chanell PCM over HDMI.
As my AV box doesn't support HDMI for audio inputs I'm currently stuck with a 2 channel input from the Miraclebox. Sometime in the near future I'll probably upgrade my AV amp, hence the question about finding out what exactly the Miracle box does output, especially for UK Freeview HD terrestrial TV. It obviously doesn't transcode into Dolby 5.1 but so far I've found zero documentation about what it does.
I have a Humax Freesat box (now retired for the Quad Plus) which did DD 5.1 over S/PDIF or HDMI from sat. The Quad Plus also does this as does the MB. I haven't come across AAC audio on broadcast yet. The Irish Freeview system is only using MPEG-2 audio at the moment although the specs for any boxes used on the system require AAC support. I presume they will turn that on at some stage when they start experimenting with surround audio, but it's not available yet.
I wasn't actually aware that Freeview HD was using AAC. I presumed it was DD (or AC3 to be more correct) like Freesat. In which case you wouldn't have an issue with S/PDIF!
The MB may well decode DD or AAC to six channel PCM over HDMI, but I'd have to swap around the boxes to check but can't do so at the moment - sorry!
Another observation
There is a difference in volume level by a (hearing) factor of 2 when tuned into a HD channel between HD programs with surround sound and HD programs without. This is not confined to the SPDIF link as it can be also heard on the right/left analogue RCA outputs from the back of the box. This has the effect that at the end of a surround sound broadcast (and even through the credits) the continuity announcer is twice as loud as the preceding content.
I wonder if the downmix for 5.1 AAC content is actually correct on a Miraclebox
I've noticed similar issues on surround content (AC-3) on satellite but it's not confined to the enigma boxes. I've also seen this on Humax boxes. Part of the issue is down to the fact that there is no volume control in operation on a DD 5.1 broadcast. You are stuck with whatever level the broadcaster sets. Try it - the volume control on the box has no function other than mute during DD (or presumably AAC) surround playback unless it's downmixing. In normal 2.0 MPEG audio the audio signal level is varied by the volume control setting on the box. You have to try and balance the normal 2.0 output by reducing the volume control to match the 5.1 output. You'll see this issue raised on various forums across all manner of boxes in the UK.
Another observation
.....
This has the effect that at the end of a surround sound broadcast (and even through the credits) the continuity announcer is twice as loud as the preceding content.Thanks. I've wondered why I sometimes need to use a volume setting of 17, and other times ~30 (that's the TV settings - I have HDMI CEC forwarding the volume control to the TV).
Now I know it's just two settings I'll know just to switch between them and not expect some programs to be in between.
Rob van der Does
30-09-14, 03:09
Do as Tony suggests: set the volume of the box a bit lower so the volume on MGP & AC3 sound is aprox the same.
You are stuck with whatever level the broadcaster sets. Try it - the volume control on the box has no function other than mute during DD (or presumably AAC) surround playback unless it's downmixing.
But it is downmixing as most (all?) AV boxes cannot decode AAC.
I can confirm that the miracle box volume control does work with a downmixed AAC signal both for live broadcast and playback. The dramatic change in volume is between a ACC downmixed non-sourround sound broadcast and a ACC downmixed surround sound broadcast. There is no way of balancing the output as suggested.
Perhaps an upgrade for VIX, and/or other images, is to have an volume offset option for surround sound content?
Sods law will however dictate that none of the UK broadcasters will adopt a common standard and those UK broadcaster noted for their technical incompetence in will break the 'rules' anyway. On commercial channels the broadcasters will use the limitations of some of the boxes to make advertisements a LOT louder than the program content (over and above the compression tricks they already used to do the same)!
Rob van der Does
30-09-14, 12:17
AV boxes cannot decode AAC.
Except those that can :)
There are indeed amps that are capable of decoding AAC. But because most AC3-capable amps can't, there is a dedicated downmix for AAC available on many boxes.
And as has been suggested before: you can turn the volume of the box a bit lower, so all PCM sound will be less loud.
But it is downmixing as most (all?) AV boxes cannot decode AAC.
I can confirm that the miracle box volume control does work with a downmixed AAC signal both for live broadcast and playback. The dramatic change in volume is between a ACC downmixed non-sourround sound broadcast and a ACC downmixed surround sound broadcast. There is no way of balancing the output as suggested.
Perhaps an upgrade for VIX, and/or other images, is to have an volume offset option for surround sound content?
Sods law will however dictate that none of the UK broadcasters will adopt a common standard and those UK broadcaster noted for their technical incompetence in will break the 'rules' anyway. On commercial channels the broadcasters will use the limitations of some of the boxes to make advertisements a LOT louder than the program content (over and above the compression tricks they already used to do the same)!
Ok - I see your issue. You're talking about the scenario where the AAC decoder in the STB is downmixing to PCM for either S/PDIF or HDMI (or even analogue audio through the phono leads) rather than passing the the raw AAC to the AV amp. My AV amp doesn't handle AAC even though it was pretty much state of the art about 5 years ago. Handles all kinds of Dolby/DTS hi-res surround you might get on a Blu-ray, but no AAC.
In my situation I have the STB set to pass DD through without downmix and control the level with the AV amp. When the programme type changes to MP2 (2.0 audio) the volume control on the STB brings the volume down to a reasonable balance. If I had DD downmix set on, then I would have the situation you're describing because you have to have AAC downmix on. I just don't have any exposure to AAC audio.
I agree with you that there's quite definitely a difference in audio levels between 5.1 and 2.0 on the BBC and ITV, quite apart from the ridiculous levels of compression used in the advertising breaks and other audio and video weirdness experienced on the budget channels where they transmit the wrong aspect ratios or play the main and narrative audio tracks at the same time.
Maybe there's something that can be done within the AAC or DD decoder settings in the software which could provide a menu control to pull down the relative audio level on 2.0 before the downmix? I know that in xbmc there are various audio level "tweaks" that can be done outside of the normal volume control. That said, xbmc is a full-featured media centre, rather than a sat/terrestrial/cable PVR box, so I wouldn't hold out too much hope of getting that level of sophisticated control in enigma images.
And as has been suggested before: you can turn the volume of the box a bit lower, so all PCM sound will be less loud.
This may work with AV amp that decodes AAC but not with any connection reliant on the downmix and output as PCM. The MB volume control controls the downmix volume for both surround sound and non-surround sound broadcasts (HDMI, SPDIF and Analogue RCA) so there will always be a perceived 2:1 difference in loudness when the broadcaster changes, which usually occurs during the continuity announcements at the end of programs or for adverts.
Set the MB volume to, say, half scale for a surround sound encoded broadcast and set the AV amp for an optimum sound level and it will change to around twice that perceived level when the broadcast program ends.
Even if you take the AV amp out of the equation by feeding the HDMI directly into a non-surround sound capable TV and using the TV speakers or using the RCA analogue outputs to an 'ordinary' stereo amplifier there is a perceived 2:1 sound level difference.
Sound balancing for UK HD terrestrial TV is probably impossible with the MB unless connected to a AAC capable AV amp that bypasses the MB downmix.
Rob van der Does
30-09-14, 13:32
Did you try the plugin 'automaticvolumeadjustment'?
Did you try the plugin 'automaticvolumeadjustment'?
Not yet - I will give it a try. At the time of writing the server is unavailable (feeds are down for maintenance) - I will try later.
Rob van der Does
30-09-14, 15:14
No: Ocram is down. Just rename the Ocram file in /etc/opkg for the moment and try again.
No: Ocram is down. Just rename the Ocram file in /etc/opkg for the moment and try again.
I changed the name and after a reboot of the box the list of plugins was downloaded.
'automaticvolumeadjustment' is not in the list. From memory, the downloaded list seems to be identical/similar to that I've seen before and is much shorter than detailed in some of the posts on this site for other boxes/images.
Perhaps that is not compatible with the VIX image or not compatible with a box configured for terrestrial TV tuners???
A Google search for the plugin resulted in some sketchy instructions in English. With no first hand knowledge, it appears that it is to balance channels and maybe assumes that the coding doesn't change between individual programs.
Rob van der Does
30-09-14, 20:34
automaticvolumeadjustment is available on the ViX feeds for my boxes.
The UK Freeview+ HD standards mandate the use of AAC-HE for broadcast use, to accommodate the sight-impaired voice over track. All Freeview+ HD compliant pvrs, like the Humax, have to transcode the AAC 5.1 signal to DD 5.1 for output via either spdif or HDMI. The signal recorded on the disc is still AAC. So if you transfer to to an external store. like a NAS or PC, you will have a file with AAC 5.1 audio. Devices like the popcornhour will output these files with 5.1 LPCM over HDMI (I have not tried spdif, but I suspect it won't work). My Pioneer SC-2022 AV receiver will handle those 5.1 LPCM channels quite easily, but it will not handle 5.1 AAC at all. I do not know of a receiver that will. So, to use the 5.1 sound from a Miraclebox, I need to copy the file to PC, and/or play it with my PCH. Otherwise, it needs to be mixed down to stereo in the MB settings.
If the Miraclebox could transcode the signal to LPCM, like the PCH, that would be very useful. It would be even better if it could transcode to AC3 5.1, but I expect there are problems with this.
I have not been able to get 5.1 LPCM over HDMI from either the MB or my Quad Plus. I'll qualify that slightly - if I try to play 5.1 LPCM it seems to be mixed down to two channels. I'm assuming it's a shortcoming of either the hardware in these boxes or else an issue with multichannel audio in enigma. For sure S/PDIF does not support 5.1 LPCM - you need HDMI for that.
Interesting that the Humax terrestrial HD box will transcode multichannel AAC to AC-3.
Rob van der Does
01-10-14, 14:48
I can't imagine any hardware to provide support for specs that deviate so much for just a few services.
The LPCM transcode works on the PCH A200 from some years back, as well as the newer models, so I suspect it is not very taxing on the processor.
I also believe that more countries will go to using AAC on terrestrial services. In fact I'm pretty sure that we're not alone already. Much of Europe is changing to T2, with H264, as the phone companies take up more and more bandwidth. We've already given up channels 61 - 68, and the channels above 50 are now under the cross-hairs.
As I said, *all* Freeview+HD licensed boxes (and others like Youview, which is not technically Freeview+) in the UK have to include the AAC to AC-3 transcoding, not just the Humaxes. A couple of boxes were launched very early which did not do this, as the requirement had a cut-off point, but those boxes are no longer on the market, having vanished along with their companies. The majority of TV watching in the UK is terrestrial.
I see this coming up in various video related forums lately, so I think it is becoming widespread.
Back to the original question.
Ignoring the SPDIF link, what comes out of the HDMI socket when the box is receiving a UK HD terrestrial broadcast with surround sound?
With no downmix is it 5.1 AAC?
With downmix is it 2 channel PCM, 6 channel PCM or something else.
If I cannot get surround sound without spending mega amounts on new equipment, which even then may not support the MB "5.1" output directly, at least I have the option of spending another 60 quid for two satellite tuners and converting my box to a satellite (Freesat) PVR with HD capability - assuming the MB supports a 7 day Freesat EPG .
I've had no luck with getting six channel PCM over HDMI out of my Quad Plus. Seems to downmix to two channels. The ViX image on any receiver will generate a 7 day EPG from Freesat.
I am pretty sure that if no downmix, it tries to output 5.1 AAC, which nothing will decode. With downmix, it outputs 2.0 AAC, which almost everything can handle.
In either case, you cannot get multi-channel.
Another observation
There is a difference in volume level by a (hearing) factor of 2 when tuned into a HD channel between HD programs with surround sound and HD programs without.There is an AutoVolume(?) plugin that might help. I've installed it and will see whether it works for FreeviewHD.
There is an AutoVolume(?) plugin that might help. I've installed it and will see whether it works for FreeviewHD.
I've now found the same. It appears that the size of the list of plugins I was getting depended on the name I gave to the renamed orcam file. Deleting the file completely now gives me the full list.
The set-up only refers to DTS/AC3 decodes not AAC needed for UK HD Freeview.
Now we have to wait for a known surround sound broadcast, possibly a Channel 4 HD modern(ish)film, Big Bang Theory on the same channel or one of the flagship programs on the BBC this weekend.
Edit - On playback of a recording where there is a transition between non-surround and surround sound it makes no difference in the 2:1 change of volume irrespective of setting in the configuration file for the plug-in. The plugin is probably not detecting the difference between aac2 and aac5.1.
The set-up only refers to DTS/AC3 decodes not AAC needed for UK HD Freeview.But that might be addressable by changing the source code of the plugin (https://github.com/OpenViX-1080p/enigma2-plugins/blob/2.3/automaticvolumeadjustment/src/AutomaticVolumeAdjustment.py) to check for AAC as well?
Specifically this at line 162:
if "AC3" in description or "DTS" in description:
Specifically this at line 162:
For interest, where did you find the source code?
For interest, where did you find the source code?The text "the source code to the plugin" is a link to it...although I agree that you can't really tell from the appearance.
Three sites of interest are:
https://github.com/OpenViX
https://github.com/OpenViX-1080p
https://github.com/E2OpenPlugins
(so those three items are links too) but don't ask me about the differences between the first two (they are not all that similar), and don't expect to find any documentation of useful information at any of them either.
@adm - I've done some more experimenting with settings. I have a Quad Plus as well as the MB Twin. On the Quad Plus I still can't get uncompressed multichannel INPUT to play properly over HDMI. I get two channels of output being played back as 48kHz PCM streams. I guess more work is needed with the drivers etc. But this is sort of specific to my particular situation where I have multichannel FLAC sound files, so maybe ignore this for the moment.
As regards AAC and DD compressed streams - my Quad Plus will pass bitstream DD 5.1 over HDMI or S/PDIF with no issues. It will also convert DD 5.1 to six channel PCM 48kHz output over HDMI if I have the multichannel option set (and also no Dolby downmix). If Dolby downmix is set you get two channel PCM output irrespective of how many channels are in the Dolby bitstream. If Dolby downmix is set, you don't get the multichannel option in the menu.
Also, on the Quad Plus, but not on the MB Twin, you get the menu option to transcode AAC bitstream to Dolby, so you could use this to pass a transcoded DD 5.1 bitstream over S/PDIF, presumably. So, in your case you could keep your existing AV amp, but would need to upgrade from the MB Twin to a Quad Plus or similarly equipped STB. I presume it's a limitation of the chipset or drivers.
Being a bit more critical in what I'm seeing/hearing
There seems to be a lip-sync problem between vision and ACC downmix audio over HDMI and SPDIF that appears uncorrectable on the Miraclebox Twin Premium. There is a PCM delay option in the AV menu with a range -1000 to +1000 but this doesn't appear to make any difference to the mismatch (audio ahead of vision).
What I'm observing is with a TV connected via HDMI and using the TV (non-surround) audio/speakers, and as a second test with SPDIF audio into an AV amplifier.
There seems to be a lip-sync problem between vision and ACC downmix audio over HDMI and SPDIF that appears uncorrectable on the Miraclebox Twin Premium. [...]
What I'm observing is with a TV connected via HDMI and using the TV (non-surround) audio/speakers, and as a second test with SPDIF audio into an AV amplifier.I'm not aware of having seen this.
There is an AudioSync extension, which might have additional options. (The relevant source files are all named AC3*, but ...).
I'm not aware of having seen this.
There is an AudioSync extension, which might have additional options. (The relevant source files are all named AC3*, but ...).
I suspect that the functions of some of the plugins have already been incorporated into the existing VIX image. There is already an inbuilt AC3 and PDM audio delay option but these don't seem to apply to to the digital audio output when viewing UK terrestrial TV. As I can only get downmix 2 channel with my (external) equipment I'm currently using the RCA outputs for audio which appear to have better (but not perfectly synchronised) lip-sync, with my set-up.
I should point out that surround sound isn't new to me. I'm on my second AV amplifier and that was purchased 6 years ago - and before that NICAM stereo on UK broadcasts. Other (4 off) equipment does work as expected with my set-up using SPDIF connections.
I'm beginning to think that with the existing hardware/software (VIX Apollo image 41) the Miraclebox Premium Twin is unsuited to UK terrestrial TV. It does a lot of things very well but is let down by it's audio capability. Perhaps I'm not surprised as its pedigree seems to be from the satellite background.
As I've said before I can adapt the box for satellite usage and this may be the way forward for me. I will try with plugins etc. for a while because watching/recording TV is not a priority for me and I must get on finishing my bathroom and refurbishing the central heating before the weather gets too cold :)
@adm - please see my post (#30) regarding the inability of MB Twin to transcode AAC to DD, whereas Quad Plus will do so. The MB also does not support HD PiP. Its chipset does not seem to be capable of supporting that. Big price difference between the MB and the Quad Plus, so it's understandable that it is not so capable.
@adm - please see my post (#30) regarding the inability of MB Twin to transcode AAC to DD, whereas Quad Plus will do so. The MB also does not support HD PiP. Its chipset does not seem to be capable of supporting that. Big price difference between the MB and the Quad Plus, so it's understandable that it is not so capable.
But is the lack of transcoding from AAC5.1 to, say, AC3 impossible due to limitations of the hardware/software in the box or just because its a low priority or no-one thought it important?
Price difference may not be a indication of potential performance. More modern chip-sets often have more functionality for a cheaper price, especially if they share some commonality with TV sets that cater for the broadcast standards world wide.
If its a software issue do any of the other possible images (OpenATV, Egami, OpenMB) do something different?
I would assume that if the drivers in the MB Twin exposed a method to do AAC to DD transcode, then it would be included in the image menu as it is in the Quad Plus. The facility is there for other boxes so no additional development needed I would have thought. Someone with in-depth understanding of the underlying image software may comment perhaps?
You could always try another image to see if AAC to DD transcode is offered. It's just a flash job. You could make a backup of your ViX image first (ViX option in System menu) so that you can easily revert. I had tried other images for the PiP restriction (SD only in PiP) as I had thought that it should support HD in the picture window according to how I had read the specs in the manual, but no image supported HD PiP.
@adm - I've done some more experimenting with settings. I have a Quad Plus as well as the MB Twin. On the Quad Plus I still can't get uncompressed multichannel INPUT to play properly over HDMI. I get two channels of output being played back as 48kHz PCM streams. I guess more work is needed with the drivers etc. But this is sort of specific to my particular situation where I have multichannel FLAC sound files, so maybe ignore this for the moment.
...
Also, on the Quad Plus, but not on the MB Twin, you get the menu option to transcode AAC bitstream to Dolby, so you could use this to pass a transcoded DD 5.1 bitstream over S/PDIF, presumably. So, in your case you could keep your existing AV amp, but would need to upgrade from the MB Twin to a Quad Plus or similarly equipped STB. I presume it's a limitation of the chipset or drivers.
I see that you are in Ireland. Do you get Freeview+HD type broadcasts with AAC5.1? If so, and you have some recordings, have you tested with off-loading one to a NAS and then playing it back on the Quad Plus (I am assuming that this is what you do with the files with flac)?
I note that you specifically state that you have the option, but not that you have tested the AAC to DD 5.1 function on a broadcast. If it is just the MB Twin that has this not working, I will seriously consider buying something else.
Earlier in the thread I said that I had no way of testing AAC as our domestic terrestrial service (Saorview) does not use AAC currently - just MP2, although the specs dictate AAC support for future use. DD 5.1 to PCM transcoding is available on the Quad Plus as is AAC to DD transcoding. You're correct in the assumption that I haven't an AAC source to test AAC to DD transcoding on the Quad Plus.
The Miracle Box Twin is a lower specced box so I assume that is why it doesn't have the AAC to DD transcode option in the menu. If you specifically need the AAC to DD transcode (or AAC to multichannel PCM decode) option then you may need to do some research with the vendors or manufacturers. In the same way that a DVB-T tuner is no use in GB for terrestrial HD reception (you need DVB-T2), you also need to be able to either transcode AAC 5.1 to PCM 5.1 or DD 5.1 depending on the capability of your AV amp. Some amps will support AAC 5.1 bitstream, but many (most?) do not.
The Miracle Box Twin is a lower specced box so I assume that is why it doesn't have the AAC to DD transcode option in the menu.
I'm not sure if they have got T2 HD and ACC decoding working correctly on the MB Twin Premium. With many HD programs with 'talking head' content there is definitely a lip sync problem which isn't apparent on SD broadcasts.
BY the way, the broadcasters are starting to use T2 for SD TV in the UK. I believe its a way of squeezing more channels into the available bandwidth.
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