[MLA] Fwd: iPhone limiting problems caused by Sound Check ?

[Bob Ludwig]

Thanks, Ian,

Who could ever have imagined that Dolby Atmos would be the driving force to make Apple turn on Sound Check by default!

Are you “mastering” any Atmos projects?  I’m still new to it, I can’t figure out how it could be Mastered without actually remixing it.

All my best,

Bob L



On Mar 3, 2022, at 7:00 PM, Ian Shepherd <ian at mastering-media.co.uk> wrote
Hi Bob,

No problem - keeping an eye on all this is an important part of running the Loudness Penalty site, at this stage.

Just to be clear, this may be an iPhone-only issue rather than a global change to Sound Check, it’s still early days so we still need to do more testing. Having said that, I get the impression that these latest changes have been made largely in response to the very large differences in level between Atmos and stereo mixes, and as such they may have been rushed through as a result, which isn’t usually Apple’s way of doing things.

I’ll keep you all posted on any reply…

Ian




> On 3 Mar 2022, at 20:12, Bob Ludwig <gatewaybob at mac.com> wrote:
> 
> Ian,
> Thank you so much for attending to these crucial matters.
> I hadn’t heard that Apple changed their once near perfect no-limiter system for Sound Check to this new unfortunate choice.  I hope they will consider your recommendations.
> 
> Best,
> 
> Bob
> 
> 
> 
> 
> 
> On Mar 3, 2022, at 2:46 PM, Ian Shepherd <ian at mastering-media.co.uk> wrote:
> 
> 
> 
> Hi All,
> 
> I just sent this message to Buddy, and thought you would be interested to see it, too.
> 
> Cheers,
> 
> Ian
> 
> 
> 
> 
>> Begin forwarded message:
>> 
>> From: Ian Shepherd <ian at mastering-media.co.uk>
>> Subject: iPhone limiting problems caused by Sound Check ?
>> Date: 3 March 2022 at 19:42:05 GMT
>> To: Buddy Judge <buddy at apple.com>
>> 
>> 
>> Hi Buddy,
>> 
>> Over Christmas I was listening to some of my favourite classical carols, on AirPods Pro and via AirPlay to my AppleTV, and was surprised to hear what sounded like quite aggressive limiting. After a bit of experimentation I discovered that if I disabled Sound Check, this fixed the problem.
>> 
>> More recently, I’ve been listening to Apple Spatial renders of Dolby Atmos again. I’m pleased to hear that the binaural encoder has been updated, and this has helped a lot with some of the tonal problems I was hearing when I first contacted you about them last year. 
>> 
>> Again however, I started hearing what seemed to be unexpected dynamics processing, and after doing some tests today I’ve found that this is also being triggered when Sound Check is enabled. (I’ve confirmed both these observations by capturing the output of the iPhone and performing null tests.)
>> 
>> In a nutshell, both the classical carols and Atmos material are being boosted in level by Sound Check, and the limiter is clamping down to prevent clipping. It’s much more noticeable on the classical material, which is being lifted considerably, but also audible on Atmos material like “Chandelier” by Sia, and “Roar” by Katy Perry, both of which are only being boosted by a dB or two.
>> 
>> This seems like a real shame, especially since the enhanced dynamics are one of the best things about Atmos, and Sound Check will now be enabled by default. Luckily I think there's a potentially straightforward fix for Dolby Atmos, since the loudest mixes are required by Dolby to be @ -18 LUFS. If the Sound Check level were simply adjusted to -18 LUFS instead of -16, this would be a big help for the Atmos material. 
>> 
>> And in fact if Sound Check simply acted to prevent level increases that would cause clipping (as it used to) this would help with classical material too, without an adverse effect on mainstream material, since the majority of material in popular genres is already quite a bit louder. 
>> 
>> I think this is quite important to sort out, because we’ve already seen lots of push-back about normalisation, and I think people will be quite upset by the idea that iOS devices are adding extra limiting.
>> 
>> Sorry for the long message, I hope all that makes sense, and please let me know if you need extra info.
>> 
>> Cheers,
>> 
>> Ian
> 
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