Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems TV Sound Volume Variability - PCM vs Pro-logic vs Dolby Digital

We have a G61RSL based TV surround system that works well. The main input is from a satellite receiver that is also functioning well. None of the sound goes via our TV and is soleley processed by an HD621 and a G61RSL.

Alternative satellite channels deliver hugely different levels of TV sound with possibly the greatest difference being between HD and non HD.

A quick search around the internet using "TV sound variability" will reveal that I am not alone in my frustration. Complaints abound but solutions do not. The solutions that are offered seem to be based upon an incomplete understanding of audio processing and system configuration. I do see that new TV models advertise things like auto-sound to counter the problem and this supports that the problem is real.

Does anyone know of a solution. I have in mind either firmware updates to the HD621 or the G61RSL.

Geoff

Geoff for my understanding could you please expand on the above, HD non HD point, and post your findings thoughts.

Thanks in advance

Hector

The difference isn't HD vs SD per se, but HD where AC3 is used as the codec. Certainly the BBC seem to adhere to some sort of AC3 movie standard meaning that to watch a normal programme, say Strictly, you have to increase the listening volume to 70, where 55-60 would suffice for non-AC3 encoded channels. It is a little irritating but not too tricky to deal with.

I think it is just a compression issue on the transmission side. I notice that 4Music is particularly bad for instance with the compression artifacts being easily distinguishable. I think we just have to suck it up unfortunately.

The worst example I know is watching The Big Bang Theory on E4 HD (Sky). The sponsorship intro is stupid loud compared to the main programme - which is in 5.1 at a much lower level. So you push the volume up to 70 for the main event and get a heart palp at the advert break.

In the end I gave up, not just because of the quite reasonable grumblings from the other side of the sofa about having to faff around with the volume all the, but my own frustration at the poor implementation - my day job is working in broadcast TV specifications and testing

I now listen to everything from broadcast in stereo as this is reasonably consistent (but not quite). If you're lucky I think a lot of 2.0 audio seems to be pro-logic (analogue surround) encoded so the 568 can extract an interesting rear pair or at least synthesize something.

V. poor.

Ian

A non-ideal solution, but one which does work is to set the Digital out from the Sky / Satellite box to PCM rather than Dolby

This provides the best solution IMHO to variable sound levels while surfing thru channels etc... and when those channels change between AC3 and PCM Output [usually the cause of the major "volume fluctuations"]

For the rare Sky Movie or other channel that might broadcast a Movie in PROPER AC3 at a decent bitrate, you can then change the Digital out back to Dolby for the duration of the movie

If you want to observe what is going on, change the display on your G61 from the usual e.g. "Digital 65"... to the next display, which will show something like "AC3 2.0" or "PCM 2.0"... and then observe how this changes between the main program and the adverts.... and eve then, this doesn't take into account the Gain that seems to be arbitrarily applied to different channels

I take an optical out from the TV to a 518 were I add 12dB gain and feed my G61R.
I listen to most TV in Trifield.

I can select sound direct to the G61 from any source too.

It's all fine for me this way. Chris. 😊

Here's an interesting question. In a stereo setup:

a) PCM from SkyHD direct into 818v3.

b) PCM from SkyHD into 518 into 818v3. 518 settings would be gain only, flat dither, and 16-bits in and out.

c) DD from SkyHD into 568.2 (down-mix to stereo) into 818v3.

I mention (c) because I've noticed that vocals on shows like "The Voice" seem more recessed via PCM than DD5.1... Having said that, my preference would probably be to go for (b). The idea of using a 518 with an 818 is really geeky; one shouldn't need to, of course, if Meridian processors had digital gain.

Hi,
Apologies for the delay. We thought we would try a few different satellite channels before replying.

Our problem, and that I believe of many others is as follows:


[*]We are using a surround sound processor in conjunction with a M HD621 and satellite receiver to listen to TV sound.

[*]The sound path is straightforward in that is passes from a satellite receiver through a M HD621 to a G61RSL surround processor. I have been careful to select HDMI 1.4 cabling and this has delivered amazing picture quality on a plasma set because of the feedback loop inherent in HDMI 1.4.

[*]Thereafter the sound is delivered to the listeners by two DSP5K's and a DSP 3300C. This is all very fine and we are happy with what we have constructed. In particular TV sound is now much more intelligible and better tweeters (I think) in the DSP5K's compensate for our diminished higher frequency auditory abilities (though they may just have the capacity to penetrate ethanol fumes).

[*]The only remaining problem is that different satellite channels produce hugely differeing sound levels. The latest test concluded that the difference is primarily between standard definition and high definition channels.

An ideal solution would be a change to the firmware of the HD621 or possibly selecting an appropriate codec to install in the HD621 but what do I know.

All the best,

Geoff

Hi Chris,

Thanks for your comment. We adopted a similar combination using optical out with good results apart from occasional very loud cracks which I still do not understand.

Our difference now is that the HD621 has been adopted to remove the TV from the equation at the suggestion of other HH's. It does seem that the HD621 passes HD video at HDMI 1.4 through to the TV which hand shakes back that it is 1080(i or p) capable. Pictures are quite stunning.

We too listen mostly in Trifield.

Best wishes,

Geoff

Hi ,

Thanks for the suggestion re changing the display. I particularly wanted to know what was being received. I shall set up the display to display the Codec in use; i.e. AC3 and so on.

All the best,

Geoff

TV channels (terrestrial DTV, satellite and, I guess, cable) may be broadcast in one of three formats:

PCM - which may or may not be Dolby Surround encoded;
DD2.0 - which is stereo Dolby Digital and usually Dolby Surround encoded;
DD5.1 - which is full fat discrete multi-channel (but which may actually contain anything from 1.0 to 5.1).

Typically, SD channels use PCM or DD5.1 while HD channels use DD2.0 and DD5.1

Different broadcasters (*) use different bit-rates for DD (2.0 and 5.1) which may have implications for sound quality. They may also send different dialogue normalisation meta-data which affects the DD decoding (I think for 5.1 only) and would be see on an M processor as a brief display something like "DialNorm -4" when the DD5.1 signal is detected (at start or after a pause).

On that technical platform, the broadcaster then vary the volume level on a content-by-content basis. So, for example, E4HD broadcasts TBBT in DD5.1 but cuts to DD2.0 for adverts, however those adverts are blasted out a stupidly high level. CH5HD seem to broadcast everything in DD5.1 but apply terrible compression which destroys the impact of car-crashes, etc. but the adverts are not too bad.

Depending on the channel then it is possible for SD (PCM) to appear loud and HD(DDx.x) to appear quiet, and vice-versa.

Another variation is that I find downloads from SkyHD to need +6 -> +8 on the volume compared with the broadcast or recorded-from-transmission versions of the same content.

The 518 option can solve (+ or -) the PCM levelling to some extent to align it with DD but cannot correct the volume of DD itself.

I don't think any of this is something that the HD621 can solve, nor even is it designed to solve it as it passes the undecoded DD signal through for decoding in the processor.

The M processor will apply your chosen synthetic surround mode to PCM and DD2.0 but note that you must set that default up separately for each of the two formats. DD5.1 (usually) invokes Cinema, to which you can apply compression for, for example, late-night listening.



(*) I'm limiting this overview to UK broadcasters