LFE (.1) channel not being downmixed

[90sNintendoKid]

I sent feedback to WiiM about this issue (ticket #520888) a month ago but haven’t received a response.

Setup:

• 2017 LG B7 OLED connected to WiiM Ultra via ARC (also tested on a TCL C845K via eARC).
• WiiM Ultra output: Line Out with subwoofer out enabled (80 Hz crossover).
• Source: Apple TV connected to TV via HDMI, playing movies through the Apple TV+ app.
• Apple TV audio settings: “Change Format” Off, Dolby Atmos disabled.

Problem:

• Watching a movie via Apple TV+ app: WiiM Ultra shows “Dolby Audio - AC3” and audio works fine.
• Playing a test video in Infuse (LFE sweep): no sound from the subwoofer during the LFE (.1) channel sweep.
• Playing test sweeps on the left or right channels: I hear sound through both the speakers and subwoofer.
• Changing Apple TV audio settings to Stereo with “downmix LFE” enabled in Infuse: I hear the LFE sweep on the subwoofer.

Can anyone from WiiM confirm if the WiiM Ultra downmixes the LFE channel in Dolby Digital 5.1 into its stereo output?

 

[DRC]

A good question. I reckon that the answer is no.

 

[Burnside]

See earlier discussion

Post in thread 'Wiim amp pro dolby lfe'
https://forum.wiimhome.com/threads/wiim-amp-pro-dolby-lfe.5319/post-88204

 

[DRC]

See earlier discussion

Post in thread 'Wiim amp pro dolby lfe'
https://forum.wiimhome.com/threads/wiim-amp-pro-dolby-lfe.5319/post-88204

So the answer is NO LFE!

 

[harkpabst]

Note:

I no longer stick to my following statement (and will update it in the other thread shortly):

Not including the .1 LFE in a 2.0 mix is actually the correct way according to Dolby specs.

Here is why.

The consensus amongst home cinema experts seems to be that the Dolby Digital specs are (or have been, as they are no longer maintained or updated) really, really sloppy. In particular, they have been mixing up actual requirements and what their own hardware decoder product has been doing. Browsing the Dolby Digital specs you can find the statement that the LFE is not included into a 2-channel downmix. But this is - according to the experts - just a description of Dolby Lab's own hardware product, and not a requirement to fulfill the specification.

Summary:

1. It looks like almost all AVRs and multi-channel processor's ever made did and do include the LFE, when calculating a 2-channel output and this is not against the specs.
2. On the other hand, Dolby proofed with their own hardware that it's not a requirement to do so.
3. We still need to ask WiiM how they handle an incoming multi-channel + LFE signal. If the above test ensures that the LFE makes it to the HDMI ARC input at all, it appears like the LFE is not included. I wouldn't bet on either option.

Regardless of what the answer is, it would never be correct to route the LFE straight to the subwoofer output!

 

[spoidyjan]

It looks like the WiiM Ultra’s handling of the LFE channel is a bit confusing. Most AV receivers include the LFE in the stereo mix, which is why the subwoofer works during test sweeps. If WiiM Ultra doesn’t do this, it could be the reason for the issue. It would be helpful if WiiM can explain whether their device follows Dolby’s rules or uses its own way to process audio.

 

[harkpabst]

Trouble is, there are no clear rules defined by the Dolby Digital standard.

When used appropriately, no content "essential" to the programme material should be contained in the LFE, but just effects enhancing the experience, mostly by added volume.

 

[rccarguy]

Just buy a AVR. Those have the suitable decoders for DD and DTS.