[MLA] AES71 comments

[Grimm | Eelco]

Dear friends,

I’m sorry I did not check my MLA mailbox the past week and did not respond more early. 

Kevin, can you please tell me under what circumstances there will be no metadata and/or guaranteed normalization level? All OTT formats I know cannot be used without metadata. Did they specify these circumstances in AES71 more precisely?

Also, what does it mean ‘-23 LUFS when there is no metadata’? If the audio is measured, metadata can be added. If the audio is not measured, it could be -6 LUFS and it is dangerous to treat it as if it is -23 LUFS.

But perhaps we are dealing with a completely different problem. The loudness of the program at the OTT service is known, with or without metadata: -23 LUFS. The question then is: how to do playback on a portable device? The solutions is to solve it in either the app (with 7 dB extra gain and a limiter) or in the OS. I will reach out to the OTT contacts at Google and Apple that Matthieu Parmentier gave me to pitch a simple solution I came up with: let the app signal to the OS that it has turned normalization on at a certain level (let’s say -23 LUFS), and then the OS offers 7 dB (in this case) extra headroom. Buddy Judge has already checked this idea within Apple and apparently the engineers have been thinking along simiar lines. You can’t fool the OS since the app needs to comply to AppStore rules and will be tested prior to release. I want to pitch this idea to as many developers within Apple as possible so chances are higher it will be adopted.

Cheers,
Eelco


> On 8 jun. 2018, at 16:41, Kevin Gross <kevin.gross at avanw.com> wrote:
> 
> I have done some work with Dolby on this but not specific to loudness. There is a standards initiative they've started to define a network format for metadata to go along with our network formats for audio and video. There are already means to carry metadata in video and AES3 and in many of the coded audio and video formats. 
> 
> I think what is mostly missing is a metadata definition for loudness. What metadata would be in a loudness dataset? I know LUFS and dBTP would be central but the devil is in the details. Are these short-term, long-term or for the entire program. If for the program, how do we know where the program starts and ends. What is needed to specify the "DRC Profile" that AES71 introduces? How does a player use all of this stuff?
> 
> Kevin Gross - AVA Networks
> 
> On Thu, Jun 7, 2018 at 12:10 AM, Ian Shepherd <ian at mastering-media.co.uk <mailto:ian at mastering-media.co.uk>> wrote:
> 
> Same. I suspect it was left vague in AES71 because it’s a massive can of worms, and they want to allow flexibility in actually implementing it.
> 
> Either way I don’t personally have the bandwidth, either as part of this group or for the AES directly.
> 
> Having said that, I think including a recognition that mobile devices may need to use a higher level as an interim measure would be a good idea.
> 
> Ian
> 
> 
> 
> On 7 Jun 2018, at 01:31, Bob Katz <bobkatz at digido.com <mailto:bobkatz at digido.com>> wrote:
> 
>> I think we'd have to bring in Dolby and other experts at least as consultants. I only understand the basics of Metadata so I'd be shooting in the dark.
>> 
>> 
>> Bob
>> 
>> 
>> 
>> On 6/6/18 5:01 PM, Kevin Gross wrote:
>>> We need to get this metadata thing sorted out. AES71 tells you when to use metadata but it doesn't say exactly what it is, how to transport it or what you should do with it. Is this something that we help could flesh out?
>>> 
>>> Kevin Gross - AVA Networks
>>> 
>>> On Wed, Jun 6, 2018 at 1:22 PM, Bob Katz <bobkatz at digido.com <mailto:bobkatz at digido.com>> wrote:
>>> I'm in favor of any solution that lowers the recommended target! But it's always interim. 
>>> 
>>> -18 LUFS is 5 dB away from -23. It ought to be safe for the majority of program with an emergency protection limiter, at least for portable devices. But I would NOT recommend -18 LUFS target for set top devices playing wide range program material on loudspeakers. There's the rub and the need for metadata.
>>> 
>>> 
>>> Bob
>>> 
>>> 
>>> 
>>> On 6/5/18 8:49 PM, Ian Shepherd wrote:
>>>> 
>>>> 
>>>>> Maybe the solution for fallback in the absence of metadata on portable devices we recommend a gain boost of 7 dB with a protection limiter. Since it's music it's likely to have a PLR of less than 16 dB so if it was normalized to -23 it would hardly trigger the limiter. But without metadata how do you know it's music? And if they normalize regular program to -23 it will be too low for many portable devices, also. 
>>>>> Shit (excuse my French)
>>>>> 
>>>> 
>>>> We’ve settled on around -18 LUFS for my podcast, which is plenty loud on my (European) iPod with stock earbuds. Anecdotally the BBC seems to be similar, and also works works fine, for the most part.
>>>> 
>>>> We should look back through our notes for the meeting where the podcast providers joined in, Bob - from memory most of them had also settled on -16 or -18, I think.
>>>> 
>>>> I assume your concern is that raising normal program to -16 would trigger excessive limiting, Bob. Perhaps suggesting -18 (which is the median of the AES recommended range) for everything would be a workable compromise, when there’s no meta-data ?
>>>> 
>>>> Ian
>>>> 
>>>> 
>>> 
>>> -- 
>>> 
>>> If you want good sound on your album, come to
>>> Bob Katz 407-831-0233 DIGITAL DOMAIN MASTERING STUDIO
>>> Author: Mastering Audio              
>>> Digital Domain Website <http://www.digido.com/>
>>> 
>>> No trees were killed in the sending of this message. However a large number
>>> of electrons were terribly inconvenienced.
>>> 
>> 
>> -- 
>> 
>> If you want good sound on your album, come to
>> Bob Katz 407-831-0233 DIGITAL DOMAIN MASTERING STUDIO
>> Author: Mastering Audio              
>> Digital Domain Website <http://www.digido.com/>
>> 
>> No trees were killed in the sending of this message. However a large number
>> of electrons were terribly inconvenienced.
> 
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