Hello forum,

Need advice if possible. I bought a 40" Digihome LED TV recently. Picture quality fine but there's a problem with the sound.

The sound from my Sky box goes via HDMI straight to my surround amp, so there's no problem there.

But I also plug a USB hard drive (with lots of video files on it) into the TV and use the TV's media player functionality. Picture is fine. I get the sound to my surround amp via the digital coax output socket on the back of the TV. Unfortunately the sound isn't working as it should.

DTS seems to be working fine.

Dolby Digital stuff seems to either play as Pro Logic OR as DD but with the surround channels sent to the front L/R speakers instead (so that the surround speakers are silent and everything sounds messed up).

I've tried adjusting the audio settings on the TV but it doesn't seem to make any difference. Have experimented with different cables, using a different input on the surround amp, etc. but it doesn't have any effect.

Can anyone suggest what might be going on and whether there's any way to fix it please?

Many thanks,
Alan.

The TV could be trying to downmix a surround format into stereo and failing miserably to get it right. Not quite sure why it would only be Dolby formats affected though.

What is the exact format of the original sound track on the files you are trying to play? Is it actually DD 5.1 or some other variant. If it was an extended format, eg 7.1 then that won't go down a SPDIF digital connection so the TV might be trying to make it fit.

But it would be interesting to know if there is any pattern to the problem.

It should be possible for the TV to transparently pass through the audio from the USB drive direct to the digital out. Make sure you have set the digital out to Multi Channel or whatever and not Stereo, PCM or LPCM (usually those three all mean the same thing, 2 channel audio).

Changing cables or amp inputs won't make any difference anyway. Unless the cable is faulty it can't change the format of the signals passing down it. Only corrupt the data so the amp can't make out if it's getting a digital one or zero. And I would seriously doubt if different inputs on the amp have different capabilities. They should all feed the same processing circuits anyway.

1) Most of the TVs with DTS processing/pass-thru only handle DTS as 2.0 and not 5.1, so are you sure you have DTS playing 'as is' or is the amp processing the signal further?

2) The fact that Sky DD plays correctly when connected to the amp is no surprise. That's as it should be. What happens to that signal if you go HDMI via the TV first?

3) The signal that flags up as DPL II originates as a stereo signal in the first place. It's Dolby Surround Encoded so it is the amp that's then processing it using DPL II. Switching the amp to "straight" would show you the signal in it's original stereo form without extracting the hidden centre and surround signal that are matrixed within. So if surround in DPL II is messed up then either the amp is decoding incorrectly (which is unlikely) or your speakers aren't hooked up right (but any direct sources would then show as messed up), or the TV is trying to add some kind of processing to the outgoing signal.

4) DD is packaged in a way that means the channel allocations are set within the signal format, i.e. DD can be 5.1, but equally you can have 2.0 encoded in DD. If it is, then the amp will only play through the front L&R speakers. The amp will be locked in DD format and won't allow you to turn that 2.0 in to a surround signal via the amps processing.

Given that these are files playing from a USB drive, and you haven't said where these files originate from ( ah-harrr Jim lad, shiver me timbers?) then how sure are you that they're encoded correctly in the first place?


It may well be that the TV is messing things up, but a little more investigation wouldn't hurt.

First, double check the amp set up. Run the test tones to be sure that the speakers are wired as you think they are. Then, as suggested above, I'd want to check what the TV is doing with a known good DD5.1 source signal both from a HDMI input and from the USB. The HDMI should be easy to sort. Either Sky or a DVD/Blu-ray player set to output bitstream via HDMI and playing the DD audio track from a DVD will do just fine. Checking the video files from USB might involve a little more work.

If I were you I would rip a DVD using makeMKV (it's free in beta) and choose the DD audio track as the one to be included. This will make a 1:1 copy of the disc for home archiving use, so you know that it's not being messed up by re-encoding or compression. Play that file back through the TV. Does the amp report a DD5.1 signal? Is the sound still messed up?

At home I run my archived DVD collection from a NAS and a USB drive in to an AV Receiver. All the files were ripped 1:1 with makeMKV, so I know it works correctly.

Thank you both. I'm very grateful for your replies. I'll look more closely later and report back...

Regards,
Alan.

The telly's sound setup options includes a "digital out" item which can either be set to "PCM" or "Compressed". By default it's set to Compressed but swapping between the two doesn't seem to make any difference.

There are some other options as well, like a "Stereo/Dual I/Dual II" option and a "Surround Sound On/Off option" but again playing around with these doesn't seem to have any effect.

I'm sure you're right re: changing cables or amp inputs. I tested it just to rule out any problems but it seems unlikely.

BTW the setup is a Yamaha DSP-E800 surround processor which sends signals to centre/surround/sub and also a pre-out which feeds into an Arcam Alpha 8 amp to give the main L/R outputs.

I'm not 100% sure about the exact formats of the original sound tracks on the files I'm trying to play. But some examples:

1. I found a "DD 5.1 test video" online which I downloaded onto the USB hard drive and played on the TV. The problem showed up here - the Yamaha senses it as Pro Logic and the surround channels are sent to the fronts instead, wrongly.

2. When I play something shown in DD on my Sky Box - the Yamaha decodes it correctly when connected directly to the Sky box but if I send the sound via the TV it comes through as Pro Logic instead. This is a nuisance.

3. DTS is working fine, can confirm that. Have a DTS download of Gravity and just checked - nice strong sound coming through the rears.

4. DD material on the hard drive seems to be playing correctly tonight - Yamaha shows it as DD and it sounds like it should. Yesterday it wasn't - it was showing as Pro Logic and the sound was messed up. I'm not sure what has changed since then. It's very peculiar.

5. I've found a DD DVD and copied it using MakeMKV as suggested. Will copy the output files onto a USB stick drive and try it out in the telly shortly.

6. Can confirm that the test tones from the Yamaha AV processor are working properly, all the speakers are wired up as they should be.

Does that provide any further clues as to what might be going on?

Thanks,
Alan.

ps I don't actually own a DVD player. And the "arrrr Jim lad" quote is right on the money

Just played the mkv files that I created from the DVD with the Dolby Digital soundtrack. This isn't working properly. Yamaha display shows Pro Logic and the sound isn't right - there's lots coming out of the surround speakers and the centre speaker but the front L/R speakers are totally silent. Can't be right, surely...?

First, I have to say that Digihome isn't a well supported brand. So the normal option of dropping on to a makers web site and downloading the user manual isn't available to us in the community. What that means is that there's no way to check the detail of how the manufacturer thinks the TV should operate. What follows then is based on experience with TVs in the general market but with the caveat that your TV may have certain quirks or differences that you're going to have to investigate yourself to validate. In short, it's best guess and some trial and error.


"PCM" is the digital version of analogue stereo 2 channel. Because of the technical limits imposed on domestic SP/DIF coax and optical connections PCM can never be multichannel. Anything transmitted via PCM will flag up as either stereo or Dolby Pro-Logic depending on the E800 settings. "Compressed" is a digital data stream. This is how DD and DTS are delivered.

These settings won't make a difference to sound from the TV's own speakers, but should change how the set deals with source signals from external sources and (possibly) its own internal tuner if it is fitted with a DVB-T2 (HDTV) tuner and set on a HD channel broadcasting in DD



Stereo/Dual I/Dual II is to do with the TV's own internal tuner and how the set switches between different languages in countries that broadcast bi-lingually. i.e English/Spanish. Since the UK doesn't use this kind of option in broadcasting then it won't apply here.


Have you checked the Sky box settings for sound (Settings > Sound >HDMI audio)? Make sure both the Digital and HDMI outs are set to Dolby D, and then green button to lock in and save those settings before exiting.

Thanks Chris.

To answer your question about the sound settings on my Sky HD box - I see the following:

Audio Output: Stereo (options: stereo or mono)
Digital Audio Output - Optical: Dolby D

...so there's no option for me to adjust the HDMI sound format explicitly. Should there be? I'm sure I read something recently about Sky HD boxes only recently being upgraded to allow DD to go via HDMI. My box is old & I'm wondering if this is the problem...

You're right. If the box is very old then it won't have the option to output DD5.1 via HDMI. Some older boxes were able to be updated, but others lacked the necessary hardware. Yours might be one. In that case then the audio via HDMI will be stereo (stereo/pro-logic) only. The Optical output is only way to get Dolby Digital for those channels on Sky that support it.

Thanks - suspicions confirmed. I might consider buying a newer Sky box in that case.

Still leaves me with the problem of the sound from the USB hard drive not being passed through the TV set properly though...does anyone have any further thoughts on that?

Alan.

I think what you need to do first of all is eliminate the Yamaha from the equation.

As you may not have a Sky box that feed Dolby Digital via HDMI to the Yamaha you can't be certain it's not the Yamaha screwing up. You could try connecting the optical out of the Sky box to the Yamaha as that should carry DD and see what happens there.

Or you could try plumbing in a DVD or Blu-Ray player and playing a variety of disks with DD and DTS soundtracks to see what they sound like.

Then once you have established that the Yamaha is perfectly OK with other sources of DD material you can then try and work out what is going wrong with the telly.

Out of interest is the telly Freeview HD? And does it have an aerial connected to it? That would be a potential source of DD from the telly which would prove that the TV optical out handles DD OK or not.

Perhaps less easy to arrange is another more modern AV amp to see if that works OK or has the same issues as your Yamaha when fed from the TV.

But I think a bit of experimentation is needed to try and locate exactly where things are going pear shaped.

I thought we'd already covered all of these bases, and in some detail, with all that had gone before? e.g Sky DD 5.1 via optical plays fine directly in to the Yamaha.

I may be missing something but I don't think he has his Sky box connected via optical? In the first post he mentions it's connected via HDMI. Can't see where he says he has tried the optical connection anywhere??

So if he does have an old Sky box that doesn't do DD over HDMI then at best he will have had Pro Logic encoded stereo through the Yamaha.

Thanks both. To clarify - yes, I already have digital optical audio going from the Sky box to my Yamaha AV processor, and it works fine - Dolby Digital broadcasts show up ok, no sign of problems.

I'm about to go on holiday for a month so I'll have to come back to this upon my return...!

On that basis then it would appear that the TV is mangling the surround information from the hard drive in some way. Or the audio track on the files you are playing is already mangled. Have to say the former seems more likely than the latter.

If you had some other surround processor to plug the telly into, or some other device to plug the USB drive into that would help confirm it is the TV at fault.

As for why the TV is doing it, that's anyone's guess. Could be a faulty example and not typical of the model. Or equally it could just be crap inherent design. You might be able to correct a faulty example of the breed by exchanging it for another one if possible. Not so easy to correct a poor design.

Thanks to all for their previous advice. Have been away for a month and busy doing other things...but returning to this now.

I've got an updated Sky HD box which has the DD output via HDMI, so that's one issue dealt with. An added bonus is that it outputs 1080i without any nasty flickering, which the old box struggled with.

As far as sound goes, I've managed to find a website http://www.demo-world.eu/dolby-dts-t...r-trailers-sd/ with lots of demo .vob files for DD, DTS, etc. I downloaded some, copied onto a memory stick and played them on the TV via its USB socket.

The DTS stuff appears to be working perfectly.

SOME of the DD stuff appears to be working perfectly too, but with others I'm not so sure - it sometimes feels like much of the signal for the rear speakers is coming out of the fronts mains instead - which is the problem I sometimes have with DD on the downloaded TV shows I tend to watch.

More experimentation needed with DD material (including stuff broadcast on Sky) needed...

Actually I tried about 15 DD test samples and all but one of them appears to be fine. Maybe the odd one is a dud file for some reason. Suggests my TV and surround amp are fine and maybe a software issue with some of the video files I've been watching...?