[MLA] AES71 comments

Sun Jul 1 17:07:20 CEST 2018

Even for systems with metadata, the standard is not very specific on what
the metadata is and how to use it to control playback.

I think we have identified important use cases where portable devices do
not get metadata. The blanket AES71 recommendation in this case is for -23
LUFS target level. We know that does not square with current practice and
recommendations. The recommendation is based on preliminary and incomplete
testing that surfaced problems with this level. I don't think it will work.

I think deficiencies in this work has the potential to cause implementers
to lose confidence in loudness standards. I am considering putting in an
official comment against AES71 to this effect.

Kevin Gross - AVA Networks

On Fri, Jun 29, 2018 at 5:08 PM, Grimm | Eelco <eelco at grimmaudio.com> wrote:

> Hi Kevin,
>
> When you say all OTT formats require metadata, can you give some examples
> and do you know details about the metadata formats and systems used?
>
>
> What I meant is that most streaming services offer their own apps and have
> a communication channel within their own ecosystem. For streaming to a
> browser you are right: in that case the metadata needs to be integrated
> with the audio stream and so it is dependent on the format. But I’m afraid
> we cannot guarantee that this will never be abused (like feeding it with
> wrong metadata). So my recommendation would be that the OS will only offer
> additional gain to approved apps, not to browsers. I agree it is not a
> complete solution, but a large majority of users (and content providers)
> will profit from it.
>
> It should work like this: in the browser, -16 LUFS will be the target
> level. Programs that are softer will sound softer. In the app -23 LUFS can
> be the target level and all content (soft and loud) will be normalized.
>
> Cheers,
> Eelco
>
> If we have good support for metadata, AES71 can work. I am concerned about
> its default behavior when no metadata is available. AES71 is not helping
> its own adoption by not at least referencing any existing metadata formats
> or systems.
>
> Kevin Gross - AVA Networks
>
> On Sat, Jun 16, 2018 at 2:11 AM, Grimm | Eelco <eelco at grimmaudio.com>
> wrote:
>
>> 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>
>> 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> 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> 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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