Dolby demonstrate their new AC-4 audio codec

Chester

Well-known Member
I feel like I've just been hit over the head with a rewind button! 384kbs AC-3 was a dinosaur after DTS came out all those full moons ago. It took a long time for Dolby Digital Plus to come out, but surely that would have been a great development bed for a better quality experience. It seems like AC-4 is just giving us what we had before with smarter packaging. A bit like a bag of crisps that's not quite full of air any more, except you also notice that there's not quite so many grams of crisps either!

I understand the motivation, but with those cuts in data I cannot believe for a minute that will decode into anything except for a overly smoothed stepped/digital or harsh sound, with lots missing. Nope, I'd need to hear it to believe it. Let's see it presented to a professional musician or sound engineer and see what they have to say.

You've probably gathered, I'm very sceptical!
 

siamsquare

Active Member
so do we need new hardware for this?
 

Chester

Well-known Member
Well it's a new codec. Stands to reason that it might be possible to do this with just a firmware update on some modern hardware, but I can see a majority of kit needing to be swapped out yes.
 

siamsquare

Active Member
Well it's a new codec. Stands to reason that it might be possible to do this with just a firmware update on some modern hardware, but I can see a majority of kit needing to be swapped out yes.
Better wait for my upgrade then!
 

stevos

Distinguished Member
32k for stereo, no matter how good the codec is, i highly doubt that is going to sound any good.

It seems the future is low quality sound tracks, put onto low quality 4k streams, just so the badges are there.
 

sarumbear

Novice Member
So Dolby decided that the sound designers don't matter and a a piece of computer code should over-ride their artistic decisions and alter the sound-track and we call this advance?

Killing artistry when we have better data data pipes, better reproduction equipment is like killing humanity. Does anyone remember what Hi-Fi even meant?
 

Drongo

Well-known Member
An interesting development that I cannot quite see the point of.

IMHO it would be pointless using it for DVD as that is a declining market and would require the launch of new hardware to decode AC-4.

Dolby already offer Dolby Digital Plus as their video streaming solution.

If they are targeting music streaming services; there is already a much better alternative in MQA which offers the highest possible sound quality in a small file.

I doubt that Blu-ray or UHD Blu-ray will want to adopt another lossy format.

I must be missing something; but if anyone can see point of AC-4 please let me know!
 

Phil Hinton

Editor
Staff member
This is intended for broadcast and with small TV speakers, not HiFi and not messing with the directors intent. It's about improving what Dolby have highlighted as an issue getting decent sound from TV audio from the built-in speakers and it offers a few solutions. At no point did they suggest it was High fidelity or replacing any existing full fat audio available on Blu-ray etc. Dolby think there is a need in a certain sector with certain consumers that they can improve and add new features.
I thought it was very interesting and the Atmos demo was impressive with just two tiny speakers in a TV set - when assessed as it is intended to be used.
 

Smurfin

Distinguished Member
I feel like I've just been hit over the head with a rewind button! 384kbs AC-3 was a dinosaur after DTS came out all those full moons ago. It took a long time for Dolby Digital Plus to come out
The differences in codecs between 448kbps DD and DTS was negligible, it was simply down to how a movie was mixed.
 

Jules

Distinguished Member
If it gets ITV (and others) to broadcast films with their 5.1 audio tracks in tact (like Channel 4 manage to do) then fair doos.

Seams a fairly limited market for this though, and isn't really addressing the future.
 
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Chinstroke

Active Member
Hopefully it is better implemented than the reduced bitrate DD+ that netflix uses which causes problems for older Sony and Denon AVR's with distortion ruining the surround sound experience. In fact the solution is to change to audio to Stereo to get rid of this. Hardly progress.
 

stevos

Distinguished Member
There is a lot of research from many angles on how to improve audio from small speakers, and whilst I never use any, I can seeing it being a huge selling feature if they crack it. They can't beat physics and make tiny speakers sound like full AV gear, but if they can make it listenable then great.
 

Monch

Novice Member
Considering how patently blind people are oblivious to crushed picture quality of streaming services (Netflix etc) compared to a good Bluray deck, or those that spend £1000s on a TV and feed it with a £100 Bluray player because "they're all the same", this latest line of bull from Dolby will be lapped up by them and journalists alike.
 

Jules

Distinguished Member
I have a number of high end plugins for music production that help make mid-bass sound like deep bass through complex psycho-acoustic
processing.

Some of them work reasonably well, but not with all material.
 

MikeTheBike2010

Active Member
I wasn't there, Phil and Steve were and state they were impressed. I remain skeptical however, for the longest time products have had special modes of audio processing which I have either turned off as they make me think my heads in a bucket (Yamaha amps simulating concert halls and 2 speaker TV pseudo surround modes to name two) or "Mega Base" buttons where I can't help but think the manufacturer built the kit then set up the mode to actually turn off the base unless you use this to switch it back on for effect (Sony iPod docks and various "midi" systems of yore!).
 

stevos

Distinguished Member
Pretty much all of us use Audessey / Dirac or equivalent, which is a pretty similar idea, mess around with the audio to create the idea of a better room.

The music modes (concerts etc) have always been pretty terrible, however sooner or later they will crack it and they will sound good. You just have to look any any tech, for example voice reconignition or VR, its slowly getting there.
 

Chester

Well-known Member
The differences in codecs between 448kbps DD and DTS was negligible, it was simply down to how a movie was mixed.
Not according to my own testing. From memory, I noticed a massive step up in performance. Wasn't DTS available up to 1.5Mbs? Here comes the old adage from the car engine world, there's no replacement for displacement.

Anyway, that's harking on about the past. Phil, like I said before, I understand the need for this, but surely in looking forward Dolby should have looked at their newer sound formats as a construct to provide audio to all consumer systems over broadcast, that of tiny TV speakers all the way up to 5.1 (let's forget everything else for now for the sake of simplicity and the nature of the application). If Dolby Digital Plus was used as a basis, more efficient algorithms used to provide reasonable quality, surely all the acoustic treatment could then be done at the decoder end with the knowledge of the system (and its limitation) in use.

Also the audio stream is so small compared to the bandwidth required for FHD video, I'm not sure where savings could be made, unless this ties in with more video codec 'enhancements'. OK, and we've witnessed this before with massive reduction in picture quality compared to when FHD broadcast first started, especially over satellite.

I appreciate you were there, saw a demo, but that's not a real-world application where the intention has been re-interpreted by a broadcaster. So I'll politely sit on the fence and see what happens. I believe it's pretty late to the party and doesn't sit well with all the talk of massively increased visual performance; for me the audio performance should go hand-in-hand.
 

Smurfin

Distinguished Member
This is intended for broadcast and with small TV speakers, not HiFi and not messing with the directors intent. It's about improving what Dolby have highlighted as an issue getting decent sound from TV audio from the built-in speakers and it offers a few solutions. At no point did they suggest it was High fidelity or replacing any existing full fat audio available on Blu-ray etc.
Everyone jumping on the negative bandwagon needs to read Phil's post again ;)
 

Chester

Well-known Member
I could probably understand such a move better if it were all about audio processing inside a TV. Dolby's been here before with noise reduction and pseudo surround, etc, and this has worked well for some. This would be a great approach to digging the best out of a sound signal and forcing it to be heard through speakers not nominally capable of such talent. Obviously AC-4 has many objectives here, I latched on to the most obvious one to me. If the system ends-up being flexible enough to provide good quality audio to all consumers regardless of equipment (we're still talking broadcast here so all things relative!), then great. Can you honestly see that working? I can't, but it's not here and just vapour right now. I have no idea what's involved to deploy it, so its implementation will be very interesting.
 

MikeTheBike2010

Active Member
Pretty much all of us use Audessey / Dirac or equivalent, which is a pretty similar idea, mess around with the audio to create the idea of a better room.

The music modes (concerts etc) have always been pretty terrible, however sooner or later they will crack it and they will sound good. You just have to look any any tech, for example voice reconignition or VR, its slowly getting there.
Just about to take the plunge and upgrade from my beloved Denon Amp (7.1 but no HDMI as so old) and looking forward to Audyssey "correction" so yes indeed I see what you mean?
 

geogan

Well-known Member
I have a number of high end plugins for music production that help make mid-bass sound like deep bass through complex psycho-acoustic
processing.

Some of them work reasonably well, but not with all material.
That must be similar to what Audyssey does with its Low Frequency Containment (LFC) settings in the high end receivers which have the Audyssey Gold package - it's supposed to remove low frequencies which go through walls and drive neighbours mad and replace them with psycho-acoustic processing so it sounds like they are still there. No idea how effective it is as I don't have it. Maybe someone here knows if it works or not - I'd be interested to know (and if you asked the neighbours if it did work or not ;))?
 

Chester

Well-known Member
Surely you can feel the difference? Genuine low frequencies will add genuine low frequency vibrations; that's what they are. If it's substituted signals, surely those vibrations disappear. I hope those signals never hit resonance of the room or something in it though. Ouch!
 

stevos

Distinguished Member
My processor has this feature (or so the marketting material says) and honestly not sure if it works or not or if its something i have to turn on / off. I should stand outside the room and try with Audyssey on and off to see if the bass is more aparent or not.
 

stevos

Distinguished Member
The main issue is for us AV fans. Its all well and good if the content sounds better on smaller devices, but not if it means it sounds naff on better gear. I completely agree that the processing should be done by the device and not at the source.
 

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