AVR Bass Management Question

[jcmccorm]

@antcollinet I understand your post (had to read it again). They (the AVR) must be doing *something*; dynamic compression, or a flat attenuation of LFE in the main channels.

The easiest approach would be what @kyuu suggested, just mix the source such that with the summed low frequency content, you never exceed 0dBFS. Then I guess the question is, did they actually DO that on this disc?

 

[jcmccorm]

The bad sound is still there even when I turn the Master Volume down to -40db. I can still hear it. I haven't tried turning down the sub trim in the AVR though. My assumption is that the trim level happens at the end of the signal chain so that turning down the Master Volume would accomplish the same thing. And if the sub signal is already clipped at that point, reducing the sub output by itself won't save it.

 

[voodooless]

The bad sound is still there even when I turn the Master Volume down to -40db. I can still hear it. I haven't tried turning down the sub trim in the AVR though. My assumption is that the trim level happens at the end of the signal chain so that turning down the Master Volume would accomplish the same thing. And if the sub signal is already clipped at that point, reducing the sub output by itself won't save it.

Try to disable the room correction. But it might just be the trim. It might nit happen at the end if the trim is separate for bass and LFE.

 

[Oddball]

Haha! Long winded post here but bear with me.

First off, @Oddball, no offense taken by your post. My first thought was just like @antcollinet , "WTF?" Then I thought, cool, ASR has a bot named Oddball, and I love Kelly's Heroes Also, I hope I'm not offending you at all here, definitely no offense meant, your post just read kind of like something AI would write.

The question is generic which should apply to all AVRs/Prepro's, but I'll get specific and give context for my question.

The rabbit-hole started when I was listening to a new (to me) ATMOS music disc for the first time, Pink Floyd's "Animals". 25 minutes into it, in the song "Pigs", I heard some deep bass that sounded clipped. It sounded obviously "wrong". My first thought was that I've screwed something up in my gain structure for the subs. Checked that and the fact that I can turn down the MV really low and *still* hear it means that it's not me. So, it must be the source.

I ripped the Bluray and extracted WAV files (8 of them for 7.1). I examined the waveforms at the "bad" spot and there was no visible clipping. I ran RTA against the WAV files (using REW) and can clearly see the the offending tone is 17Hz. My subs are all sealed so there's no chance of port noise. (17Hz is close to where a lot of people tune their ported box to so a valid assumption would be port noise).

So it's not me, and I couldn't see anything in the source waveforms, so the only thing that I have ZERO visibility into is what the AVR is doing when it sums low frequency content from all bed-layer channels. Is it possible my AVR is clipping the sub output?

I'm using a Panasonic 820 player and the AVR is a Yamaha A8A.

My understanding of the way the LFE channel is handled is that the mixer (source) attenuates the LFE by 10db and the AVR adds it back internally.

Let me go back and read all the responses over again. I didn't completely grasp it all so my question may indeed be answered. I didn't see anything beyond speculative answers (which is completely fine) but I need to understand it better so I can possibly test the theories somehow. (Really what I need is a way to mix my own 7.1 content with low-frequency test tones in all channels and view the analog preamp outputs with a 'scope to see what happened in the AVR).

I am glad that you took no offence and welcome to ASR. It's not just my screen name. Lots of Odballs around here. But lots of them have their great points as well, despite the fact that they might in throw in more confusion that a bot.

I am out of my depth with Yamaha. And perhaps some other members could be more helpful. In general it helps to set your subs at the lowest AVR gain possible so they can have plenty of headroom. Not sure about this particular trac, but some material is not that well mastered even against the reference systems. If the clipping is isolated to this track, I would just forget about it.

You would need to check your settings on Y - if you have YPAO engaged, it could do something to facilitate clipping. In general, we do check our room EQ independently with REW. It really gives a better perspective on what is actually happening.

 

[antcollinet]

@antcollinet I understand your post (had to read it again). They (the AVR) must be doing *something*; dynamic compression, or a flat attenuation of LFE in the main channels.

The easiest approach would be what @kyuu suggested, just mix the source such that with the summed low frequency content, you never exceed 0dBFS. Then I guess the question is, did they actually DO that on this disc?

I don't think they do it on the disk, because summing is different depending on the ARV speaker set up. It will be done on the AVR - and only then when it is summing channel bass - "large" speaker bass is not summed.

Like this:
How many channels are we summing? Turn down the level by this factor (eg summing 7 channels, turn down gain by factor 7.

What I don't know is if it will then subsequently turn up the sub analogue output gain by the same amount. Or if that will be done as part of the room setup process where it measures the sub, and tells you to adjust the gain if it is too hot/cold.


Note - This is pretty speculative - based on the discussion in this thread. I have no evidence of what actually is happening.

 

[3ll3d00d]

If the low frequency content for all channels (content under the crossover frequency) in the source is near 0dBFS in level (maximum level), how does the AVR avoid clipping the subwoofer output (exceeding 0dBFS) after summing all of the channels plus LFE?

Do all manufacturers handle this the same way?

historically the answer is "they didn't, they'd just clip and it's left as an exercise for the user to work out where/how this clipping happens and whether you can avoid it by use per channel attenuation (which would vary by model)", this has been demonstrated many times over the years on avsforum. Whether currently available models behave the same way is another Q and one you'd need to determine by measuring the output from any given device (IMO it's reasonable assumption they will clip as the above behaviour was widespread back in the day).

 

[Oddball]

I don't think they do it on the disk - it will be done on the AVR - and only then when it is summing channel bass - "large" speaker bass is not summed.

Like this:


How many channels are we summing? Turn down the level by this factor (eg summing 7 channels, turn down gain by factor 7.

What I don't know is if it will then subsequently turn up the sub analogue output gain by the same amount. Or if that will be done as part of the room setup process where it measures the sub, and tells you to adjust the gain if it is too hot/cold.

By the book - you are summoning all the channels at the same time. So subs at 115dB peak and others at 105dB peak. If sub can't handle that well too bad. But as I noted, one off track should not be an issue. I had issues in the past with multiple tracks - but admittedly so because my bass response was not even. I can't say that anything is clipping my system nowadays.

 

[antcollinet]

If sub can't handle that well too bad.

It (the question) is not about the sub (as I understand it) - it's about exceeding 0dbFS in the digital pipeline internal to the AVR.

 

[jcmccorm]

Found something interesting from googling. "Bass Management and the LFE Channel" by Anthony Grimani (pretty sure that guys knows some things ) at Sound and Vision.

Bass Management and the LFE Channel

Bass is like salt. Really, it is. Salt is a seasoning, a treat that we add to good food to make it taste even better. Bass is the same way. A sound system without it lacks the last little element that transforms an ordinary activity like listening to music or watching a movie into an...

www.soundandvision.com

On page 2, he says this:

"There is NO NEED for an LFE channel in the vast majority of music applications. There continue to be multichannel music recordings released with content in the LFE channel when the bass in the main channels isn't even close to overload. Inexplicably, some music-recording engineers think that they must put something into the LFE channel so that end users will hear sound coming from their subwoofers.

Frankly, that's terrible logic because the subwoofers in bass-managed systems (which represent the overwhelming majority) receive the LFE channel and the sum of the main-channel bass. Users and installers of multichannel systems don't really need to worry about a music recording with an LFE channel as long as they set up their systems correctly with bass management. At times, however, bass-managed playback systems dig up bass that recording engineers didn't hear because their monitoring systems weren't bass-managed and their monitor speakers weren't full-range. This unmonitored bass sounds ultra-funky, and there's absolutely nothing users can do about it without reconfiguring their systems every time they switch discs. It's time for us to lodge some complaints with the production community!"

Interestingly, when viewing the waveforms from the Bluray in Audacity, the only activity I see in the LFE channel is where the "bad" sound is. So, speculating some more, I think that Anthony is saying that low frequencies from bed-layer channels will never clip when summed, but when the LFE is added, it could. Further, he blames the producer for this. So this could be what I'm hearing. It doesn't answer my question though about what the AVR is doing, but it makes me feel better knowing that someone in the industry has observed this phenomena.

 

[antcollinet]

That's really interesting - and may well relate to the issue you are hearing.

but when the LFE is added, it could.

I read it more that the sound engineers add bass that they can't hear because they are not using speaker systems that make it audible. When that is made audible on your system, it sounds bad - not due to clipping but because it hasn't been mixed properly.

At times, however, bass-managed playback systems dig up bass that recording engineers didn't hear because their monitoring systems weren't bass-managed and their monitor speakers weren't full-range. This unmonitored bass sounds ultra-funky....

 

[Oddball]

Found something interesting from googling. "Bass Management and the LFE Channel" by Anthony Grimani (pretty sure that guys knows some things ) at Sound and Vision.

Bass Management and the LFE Channel

Bass is like salt. Really, it is. Salt is a seasoning, a treat that we add to good food to make it taste even better. Bass is the same way. A sound system without it lacks the last little element that transforms an ordinary activity like listening to music or watching a movie into an...

www.soundandvision.com

On page 2, he says this:

"There is NO NEED for an LFE channel in the vast majority of music applications. There continue to be multichannel music recordings released with content in the LFE channel when the bass in the main channels isn't even close to overload. Inexplicably, some music-recording engineers think that they must put something into the LFE channel so that end users will hear sound coming from their subwoofers.

Frankly, that's terrible logic because the subwoofers in bass-managed systems (which represent the overwhelming majority) receive the LFE channel and the sum of the main-channel bass. Users and installers of multichannel systems don't really need to worry about a music recording with an LFE channel as long as they set up their systems correctly with bass management. At times, however, bass-managed playback systems dig up bass that recording engineers didn't hear because their monitoring systems weren't bass-managed and their monitor speakers weren't full-range. This unmonitored bass sounds ultra-funky, and there's absolutely nothing users can do about it without reconfiguring their systems every time they switch discs. It's time for us to lodge some complaints with the production community!"

Interestingly, when viewing the waveforms from the Bluray in Audacity, the only activity I see in the LFE channel is where the "bad" sound is. So, speculating some more, I think that Anthony is saying that low frequencies from bed-layer channels will never clip when summed, but when the LFE is added, it could. Further, he blames the producer for this. So this could be what I'm hearing. It doesn't answer my question though about what the AVR is doing, but it makes me feel better knowing that someone in the industry has observed this phenomena.

We can be posting all day long what is mixed and how it is mixed and how it impacts our systems. If isolated to some tracks, probably best to ignore it.

Best way to avoid clipping in the low end is to have sufficient firepower for whatever your need, and have it reigned in with some decent EQ system that will also cater to your needs. If you have a +10dB bump in your sub range, it will likely clip if your subs are not good for that (aka 115dB reference + 10dB, plus whatever your bass curve might be - this could take you to 130+dB theritory).

My subs don't really clip as they have a DSP that avoids that - very grateful for that as did not know when I was buying them, or how important that might be for the bass heads.

 

[jcmccorm]

That's really interesting - and may well relate to the issue you are hearing.



I read it more that the sound engineers add bass that they can't hear because they are not using speaker systems that make it audible. When that is made audible on your system, it sounds bad - not due to clipping but because it hasn't been mixed properly.

Yes, I think your right. Not clipping, but it sure sounds wrong.

 

[EWL5]

Haha! Long winded post here but bear with me.

First off, @Oddball, no offense taken by your post. My first thought was just like @antcollinet , "WTF?" Then I thought, cool, ASR has a bot named Oddball, and I love Kelly's Heroes Also, I hope I'm not offending you at all here, definitely no offense meant, your post just read kind of like something AI would write.

The question is generic which should apply to all AVRs/Prepro's, but I'll get specific and give context for my question.

The rabbit-hole started when I was listening to a new (to me) ATMOS music disc for the first time, Pink Floyd's "Animals". 25 minutes into it, in the song "Pigs", I heard some deep bass that sounded clipped. It sounded obviously "wrong". My first thought was that I've screwed something up in my gain structure for the subs. Checked that and the fact that I can turn down the MV really low and *still* hear it means that it's not me. So, it must be the source.

I ripped the Bluray and extracted WAV files (8 of them for 7.1). I examined the waveforms at the "bad" spot and there was no visible clipping. I ran RTA against the WAV files (using REW) and can clearly see the the offending tone is 17Hz. My subs are all sealed so there's no chance of port noise. (17Hz is close to where a lot of people tune their ported box to so a valid assumption would be port noise).

So it's not me, and I couldn't see anything in the source waveforms, so the only thing that I have ZERO visibility into is what the AVR is doing when it sums low frequency content from all bed-layer channels. Is it possible my AVR is clipping the sub output?

I'm using a Panasonic 820 player and the AVR is a Yamaha A8A.

My understanding of the way the LFE channel is handled is that the mixer (source) attenuates the LFE by 10db and the AVR adds it back internally.

Let me go back and read all the responses over again. I didn't completely grasp it all so my question may indeed be answered. I didn't see anything beyond speculative answers (which is completely fine) but I need to understand it better so I can possibly test the theories somehow. (Really what I need is a way to mix my own 7.1 content with low-frequency test tones in all channels and view the analog preamp outputs with a 'scope to see what happened in the AVR).

There’s no way you are analog out audio from the Panny to the Yamaha, is there?

 

[jcmccorm]

Funny you should mention that I was proof-reading my message before posting and saw that I didn't state the connection between the player and AVR; analog could pose problems since I'd be using the player's bass-management. I thought "nah, it's implied".

So shame on me for not clarifying that connection and thank you for catching that so I could update.

The connection between my player and AVR is HDMI so bass-management is all in the AVR.

 

[peng]

Sorry, my mistake. It’s the other way around: it’s encoded 10 dB lower, and the processor brings that back again at playback. That just means that 0 dBFS of encoded LFE is 10 dB louder than the other channels.

Now you've got it covered, finally.

 

[peng]

The connection between my player and AVR is HDMI so bass-management is all in the AVR.

In that case, and assuming you output it in bitstream, the input to the AVR will have the LFE channel content 10 dB lower, and as you mentioned, the AVR will boost the LFE's LFE channel content output by 10 dB so all is balanced. Is it possible that the contents you played just happened to have a lot of bass in one, or all channels such that when summed altogether the subwoofer amp would be clipping? The fact is, if the signal is high enough to the input of an amp to push that amp to its clipping point then it will clip; and that could be just what happened.

 

[jcmccorm]

In that case, and assuming you output it in bitstream, the input to the AVR will have the LFE channel content 10 dB lower, and as you mentioned, the AVR will boost the LFE's LFE channel content output by 10 dB so all is balanced. Is it possible that the contents you played just happened to have a lot of bass in one, or all channels such that when summed altogether the subwoofer amp would be clipping? The fact is, if the signal is high enough to the input of an amp to push that amp to its clipping point then it will clip; and that could be just what happened.

Thanks @peng! There absolutely is a lot of bass content in the other channels (7 bed-layer channels). I'm more concerned that the AVR itself is clipping, or at least compressing, the sub output because of all the summing in the bass management logic.

I don't think that the subwoofer amp is clipping. Here's a compression run, but I stopped at 115db and I don't ever listen anywhere near this level. Besides, this issue is still audible when the master volume is turned down to -40db which should eliminate the chance of clipping.

 

[EWL5]

Thanks @peng! There absolutely is a lot of bass content in the other channels (7 bed-layer channels). I'm more concerned that the AVR itself is clipping, or at least compressing, the sub output because of all the summing in the bass management logic.

I don't think that the subwoofer amp is clipping. Here's a compression run, but I stopped at 115db and I don't ever listen anywhere near this level. Besides, this issue is still audible when the master volume is turned down to -40db which should eliminate the chance of clipping.

View attachment 520445

I don't think you've mentioned where you've set the crossover frequency, have you?

 

[Keith_W]

That is a very impressive subwoofer! May I ask what it is?

 

[peng]

Thanks @peng! There absolutely is a lot of bass content in the other channels (7 bed-layer channels). I'm more concerned that the AVR itself is clipping, or at least compressing, the sub output because of all the summing in the bass management logic.

I don't think that the subwoofer amp is clipping. Here's a compression run, but I stopped at 115db and I don't ever listen anywhere near this level. Besides, this issue is still audible when the master volume is turned down to -40db which should eliminate the chance of clipping.

View attachment 520445

If MV was at -40 or even -20 then the AVR would not be clipping.

Have you tried to lower the sub amp’s volume to say below 9 O’clock, or lower? Just to narrow things down..