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Why is Multichannel PCM 5.1 softer than Dolby Digital 5.1 on my Arc 5.1 setup?

  • 10 March 2021
  • 5 replies
  • 7408 views
J
Badge +2

Hi Everyone,

This is giving me the s**ts and was wondering if someone can assist me. Even better if Sonos chimes in and tell me they are working on it!

My setup is  Apple TV 4K → HD Fury Acana → Sonos Arc 5.1 (ARC + 2X Surrounds + Sub).

When I tell the ATV4K to keep the default format (which includes Atmos), when I watch a 5.1 show which isn’t Atmos, it plays at Multichannel PCM 5.1. This is to be expected, but what isn’t expected is that the volume of the PCM appears much softer and less punchy than if I were to tell the ATV4K to use Dolby Digital 5.1. The sound quality between the two is negligible, so I can’t say “...well MPCM is lower volume, so although I have to turn it up higher, at least the sound quality is much better”.

We are talking about very noticeable differences here. What is going on? I would actually expect the Multichannel PCM 5.1 to pull trumps here. This is super annoying because, with this issue, I have a tendency to have it overriding to DD 5.1 on the ATV4K, but when I want to go and watch an Atmos show, I have to go back into the settings and change it to the default setting.

 

Sonos: is this problem in hand with you??

 

Any help appreciated!

 

 

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Best answer by Corry P 16 March 2021, 12:06

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5 replies

Corry P
Userlevel 7
Badge +18

Hi @JiminLondon 

Thanks for your post.

As Atmos is passed to the Arc, the Arc needs to convert it internally to LPCM so it can be played (PCM is the only format Digital to Analogue Converters actually understand). As this happens, the Arc checks it’s dynamic range compression setting and applies that to the stream. When you play LPCM at the source, the Arc no longer needs to convert the compressed stream, but it also loses the opportunity to apply it’s dynamic range compression settings - this is done instead by the source device. I suspect your Apple TV has dynamic range compression disabled, while your Arc has it enabled (called Night Sound in the Sonos app). The Arc’s Loudness setting could also be a factor.

Please see our Reduce loud TV audio with Night Sound page on how to activate/deactivate Night Sound. You can find the Loudness setting in Settings » System » [room with Arc] » EQ » Loudness.

If that doesn’t produce the desired effect, please try adjusting the same setting on your Apple TV: https://support.apple.com/en-gb/guide/tv/atvba773c3c9/tvos

I hope this helps.

"Common sense is the collection of prejudices acquired by age eighteen." - Albert Einstein
J
Badge +2

Hi @Corry P,

Thanks for your reply but what you have mentioned isn’t the cause of the issue. Both “Reduce Loud Sounds” on the ATV and the “Night Sound” mode on the Sonos are disabled.  Loudness is enabled.

This is part of the reason why it is giving me the sh**ts, as all settings are what they should be. Atmos sound quality is fine. The issue is between Multichannel PCM 5.1 and DD 5.1

I really do think this is a bug on the Sonos side. Multichannel PCM 5.1 audio should sound the same, if not better than forcing the ATV to output DD 5.1 ...not softer! Not unless someone can prove to me that the softer audio on MPCM 5.1 (and the need to turn up the volume) is there for very valid reasons.

I am getting close to having to return all of this kit. @Sonos, can you help?

 

 

Smilja

PCM is inherently softer than Dolby Digital or Atmos.

»And the world is like an apple whirling silently in space, Like the circles that you find in the windmills of your mind.« (›Windmills Of Your Mind‹ [1967]. Music by Michel Legrand ; English lyrics written by Alan & Marilyn Bergman)
J
Badge +2

Hi @Smilja  Thanks, can you give me a bit more information as to how and why this is the case? Can you point me to some links which back your comment up etc? I still find it odd that I need to turn the Sonos up to close to 90% just because it is PCM when I only need it at about 60% on DD 5.1. This just can’t be right!

Corry P
Userlevel 7
Badge +18

Hi @JiminLondon 

90%? I recommend you get in touch with our technical support team, who have tools at their disposal that will allow them to give you advice specific to your Sonos system. As @Smilja mentions, some codecs just sound different, but I would think 90% is excessive to just make things audible.

"Common sense is the collection of prejudices acquired by age eighteen." - Albert Einstein
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