I'm not an audio engineer (by any stretch of the imagination), but I believe the volume differences between the various different sound channels are down to more sound channels (5.1, 7.1 etc) being broadcast, but are not being fed through a supporting amplifier for the correct amount of channels, but rather a two channel/stereo amp in your case. This will take away control of the unsupported channels as those will be fed through the only two channels that are available. Volume control will thus be restricted to just two channels, but said two channels will contain the sounds for five other channels that you will have no control over their individual volumes.

Hope that makes sense ?...

Only one setting - depending on the source material, it can be too much or not enough. Does it work for all outputs, or only for its built-in speakers?
I have a 5.1 system: the volume of the speakers should be set once (depending on their relative distance). There's no simple volume control - you have to dive into the settings.

I guess you could make custom profiles and switch between them, if that's possible. Yet, Dolby/DTS sounds/channels are rarely completely separated (e.g. main voice only in the middle, main effects only L/R, the rest F/B).

I have a lot of DVDs - few of them have good/impressive surround mixing. For most most of them, the non-front channels sound like an afterthought.

That depends on the equipment in question. Dolby Digital has Dynamic Range Control as a feature of the decoder so the setting there should work on the output of what's being decoded. Eg, if you enable it on a TV, then whatever output (speakers, headphone, etc) that gets sent to should be affected. But if it's say a DVD player or digital TV box that's setup to digitally "passthrough" the audio (eg over SPDIF to an amp / receiver), then it won't and the receiving equipment will need that feature enabled instead.

Yeah, that would (or should) be the case, or at least possible, but the OP has a stereo amp, and I guess that it is only feeding two speakers, which would imply removal of their ability to adjust the volume of the other channels not supported in a two channel setup.

Thanks AB2012, your input is as always helpful.

I had a quick look at the TV, but will need to investigate further.

Not sure how much actual true control a TV has on it's sound output though and even if mine does support such a feature, it should not be required in my opinion. The sound signal should pass to the TV and not need any post processing. WIll check though and post back.
This is what I suspect is part of the problem.

Too much tinkering by sound engineers into "surround sound" combined with low quality/low bandwidth broadcast options.

None of this happens with true sources, for example bluray/dvd or even streaming though I am still experimenting with the latter.

I will be watching Venom tonight and also recording so I can try a few things out. I suspect that even the act of recording has an effect on the sound output (perversely for the better so far but again I am still experimenting here).

Technically speaking, anything you do to the incoming signal is post processing. It's not like modding a game, changing textures...

Very true.

However, I am currently only amplifying a source signal. At this point the TV is only really a receiver of the signal.

I have to go now, for the experiment is about to start. Will post back if I find any results.

Well it didn't take long to see where the problem lay.

The sound from Channel4 (for films anyway) seems to be pushed out at a very quiet level indeed- hence the need to crank up the volume in order to hear dialogue and hence the reason that loud sections sound really loud. The entire film is just broadcast at far too low a level.

It can clearly be heard once the commercials kick in- they are not actually overly loud but sound louder as the amplification was already cranked up for the film.

My amp usually sits about the 9/10 oclock position for TV listening, for Channel4 it has to go well past 11.

Whether or not this is purposeful on the part of Channel4 is up to you to decide. I flipped between channels to test this and all other channels that I tried were far too loud at the volume necessary to listen to Channel4.

I am not going to bother complaining to Channel4 over this as I have previously found them to be most unhelpful and I have found that their service is not really worth the effort anyway, especially with regard to Film4 which these days is really just a shadow of its former standing.

Thanks to all for posting your thoughts and advice, it was most helpful.

far as i can tell (thus far) its voodoo people. gonna have to listen through though

Yup, that's no 'accident' at all. Just do what I do and hit mute when the commercials come on. Your sanity will thank you as much as your ears... ;-)

These are common issues, but my understanding is that the low dialogue volume is a recognised trend in film audio mixing of late. Adverts being extremely loud has been the norm for quite a long time and it's deliberate. They likely brickwall limit the hell out of them to make sure they're as loud as they can possibly be. Films and TV programmes will by comparison have a much greater dynamic range.

The reduced dynamic range you noticed with Netflix may be some soft automatic volume levelling they're applying. That's actually a lack of dynamic range compression rather than something caused by dynamic range compression.
If the entire film was broadcast at too low a level it wouldn't increase the difference between the quiet parts and the loud parts. That difference is baked in by the sound mixing of the film. The film obviously just has a wider dynamic range than you'd like. Have a look in your TV settings for "AVL" or "night mode".

As has been pointed out by others, adverts are generally in a loudness war with each other and will probably be brickwall limited to hell. Channel 4 probably aren't broadcasting the film too quiet, it's just that the adverts are as loud as they can be all of the time while the film is only occasionally as loud as it can be because it actually has dynamic range.

They can't turn the volume of the film up because the loud parts would exceed 0dB and clip. They could run the film through a limiter, but that would be far worse. Such processing should be applied by the watcher's own system, not blanket applied to the entire broadcast.
I imagine they are contractually obliged not to turn the volume of the adverts down.