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Do AVR processors compress the audio if select NONE for center channel speaker?

373 Views 7 Replies 5 Participants Last post by mtrot, Sep 19, 2019

mtrot

Discussion Starter · Sep 16, 2019

It seems like I read some time back that the absence of a center speaker will cause some sort of compression in multi-channel film tracks. I'm not sure if this was with DTS or Dolby, or both. Anyway, I was watching Jurassic World Fallen Kingdom recently, and it seemed like the T-rex roar was just not as loud as it should have been, considering the volume setting. I do not have a center speaker at this point and selected "NONE" in the setup for center channel speaker. Any info much appreciated.

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Leeliemix

· #2 · Sep 16, 2019

Afaik the AVR just puts the center info in both left and right main speakers at the correct combined volume.

How impressive the roars are depend a lot on your speakers and sub but they also differ in the mix so some are louder then others.

Sent from my iPad using Tapatalk

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JonfromCB

· #3 · Sep 18, 2019 (Edited)

As much as I'd like to think processors and manufacturers licensed to process specific recorded codes are standardized, reality tells me they are not. I generally agree with Leeliemix...but I have wonder how much the AVR processors differ and/or how they process source materials. For example; when a source was recorded in say Dolby Digital surround and then processed through an AVR for playback on one of manufacturer's playback effects such as "rock", "jazz", "small club", "opera house", "stadium" "neural surround" "multi-channel"...yada yada yada, that clearly are not that AVR's default "DDS" setting one can only guess what the AVR is doing to the signal. And that raises the same question of how any given AVR/manufacturer decodes and up or down mixes some other source material typically recorded and coded in 2 or 3 channels and then decoded and processed for playback in any other format different from the primary code of source material...ie, stereo, DTS, THX, multi-channel stereo. I'm guessing there is a lot "going on" with the signals except perhaps except for simple stereo recordings played back through what most AVRs refer to as "direct", "pure" or "stereo" mode. What we know for sure is that any source recording with center channel content that is being played back through a system without a center channel is down-mixing that information somehow and I doubt that signals are just removed because there is no speaker to send it too. Best advice I have is let your ears be your guide as to what you like, just know that except for 2 channel only recordings or FM, far and away the majority of video source material including streaming and broadcast/cable include center channel signal material.

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sdurani

· #4 · Sep 18, 2019

mtrot said:
It seems like I read some time back that the absence of a center speaker will cause some sort of compression in multi-channel film tracks.

If you split the info in the Centre channel to the Left & Right speakers, then it has to be lowered (compressed?) by 3dB to keep that info at its original level since it's now being reproduced by 2 speakers.

Also, the newly created Left & Right channels now have 2 channels worth of info downmixed into them: new Left channel = Left+Centre info and new Right channel = Right+Centre info. If, for example, the Left info and Centre info happen to peak simultaneously, then the downmixed Left channel is going to overload (distort). So the original Left & Right info have to be lowered 3dB as well.

Your receiver should automatically raise the L/R speaker trims to compensate for lowering the L/C/R channel info.

I was watching Jurassic World Fallen Kingdom recently, and it seemed like the T-rex roar was just not as loud as it should have been, considering the volume setting.

Raise the volume setting till it's as loud as it should have been.

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mtrot

Discussion Starter · #5 · Sep 18, 2019

I understand all of what you guys have posted, but the question is if the Dolby processor compresses the audio by default when the center channel is not active. I read that somewhere a few years ago, but cannot find that info now. This is with Dolby True HD if I remember correctly.

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sdurani

· #6 · Sep 18, 2019

Yes, happens by default, for all audio sources, not just Dolby (it's not like DTS codecs or even uncompressed PCM are somehow immune to overloading/clipping when two channels are combined).

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craig john

· #7 · Sep 19, 2019

mtrot said:
I understand all of what you guys have posted, but the question is if the Dolby processor compresses the audio by default when the center channel is not active. I read that somewhere a few years ago, but cannot find that info now. This is with Dolby True HD if I remember correctly.

All codecs will reduce the levels. However, this is not the same as DRC or Dynamic Range Compression, (aka "Night Mode.") As Sanjay described it is a level reduction of the individual channels to accommodate the additional signal, so as not to overdrive the channels. The overall dynamic range of the *system* is NOT reduced.

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mtrot

Discussion Starter · #8 · Sep 19, 2019

I knew I had read something about Dynamic Range Compression when no center channel speaker is present. Here is an AVS thread that touches on it.

https://www.avsforum.com/forum/89-speakers/2927702-ill-effect-phantom-center.html

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