Why bass management makes my life tedious

[Soundmixer]

We strayed off topic here (my bad) but none of this really affects the BM situation, which all exists post-render. Ha, interestingly though, the issue with BM is that it's a mono downmix of all speakers so doesn't maintain level regardless of pa

Not exactly. The RMU in the home version of Atmos has limiters on both the mains (which addresses the bass build-up when BM is employed), and the LFE. Dolby recommends we leave both of these limiters on to maintain the spectral balance when monitoring, remastering, and encoding a cinema mix to HT.

 

[FrantzM]

Most of these filmmixers mixes is rubbish Near Field atmos trash.

Hi

I don't share that dim view of the ,sometimes marvelous work of modern-days movies sound designers or mixers. I also consider Atmos to be a real advance in movies sound. I find modern days movies sound to be better than the old ones. I also do not share your passion for Laserdiscs as I find BD much better and 4K HDR in another galaxy. Granted our references differ, I have a very modest system a BenQ HT20150A, Stewart Screen, 3 LSR 308 , 2 LSR 305 for surround and now 2 LSR 305 for Atmos plus 2 subwoofers, comparing to your professional cinema gear ... Still I find the soundscape of modern movies most remarkable and enjoyable.

My issue is that I prefer to listen to music in 2-channel. I have had to calibrate the audio system (Main + 2 Subs) differently for Music/2-Ch and Video MCH/Atmos when present. It is due to the fact that in my small room, my current speakers especially the 3 JBL 308 are quite capable of going low, around 45 Hz or even below... In movies/MCH, I have to contend with those 3 additional low frequency radiators. I'e used REW for 2-Ch but have left Audyssey take care of the MCH. I know it is not optimal nor am I entirely satisfied with the system on MCH/Atmos, I enjoy it on movies nonetheless... a lot. Would like to find a better way to have the best of both worlds.

Peace

 

[AdamG]

Insulting posts removed. Our apologies. Please resume this most interesting conversation.

 

[markus]

Not exactly. The RMU in the home version of Atmos has limiters on both the mains (which addresses the bass build-up when BM is employed), and the LFE. Dolby recommends we leave both of these limiters on to maintain the spectral balance when monitoring, remastering, and encoding a cinema mix to HT.

Where exactly in the signal flow get these limiters applied?

 

[markus]

no standards

That's the real problem. For obvious reasons Dolby has failed to enforce meaningful standards. In my opinion stricter standards have to come from the major film studios.

 

[Soundmixer]

Where exactly in the signal flow get these limiters applied?

In the encoding process.

 

[markus]

In the encoding process.

So you can't monitor the actual results during mixing as it's not part of processing in the RMU?

 

[audio2920]

Not exactly. The RMU in the home version of Atmos has limiters on both the mains (which addresses the bass build-up when BM is employed), and the LFE. Dolby recommends we leave both of these limiters on to maintain the spectral balance when monitoring, remastering, and encoding a cinema mix to HT.

It does, and that may help under saturation conditions. But surely the limiters wont touch the imbalance until then?

[edit - making that last sentence a question rather than a statement. I've always thought the limiter threshold is right at the top, around -1dBTP, but maybe it's got a touch of compression just below that?]

 

[audio2920]

Insulting posts removed. Our apologies.

Thank you

 

[audio2920]

So you can't monitor the actual results during mixing as it's not part of processing in the RMU?

The RMU has a limiter with the exact same characteristics, which you can optionally engage in the monitor chain to hear what it'll be like once the "real" limiter is applied. AFAIK this is just for the monitoring output.

 

[Soundmixer]

It does, and that may help under saturation conditions. But surely the limiters wont touch the imbalance until then?

[edit - making that last sentence a question rather than a statement. I've always thought the limiter threshold is right at the top, around -1dBTP, but maybe it's got a touch of compression just below that?]

You can address that imbalance before encoding.

 

[markus]

The RMU has a limiter with the exact same characteristics, which you can optionally engage in the monitor chain to hear what it'll be like once the "real" limiter is applied. AFAIK this is just for the monitoring output.

Thanks.

Regarding bass buildup in the redirected subwoofer channel in a bass managed home theater environment. What's the worst case scenario? Does the encoder or the delivery format (DD+, TrueHD or PCM MAT) put a limit on it in any way?

 

[Soundmixer]

Thanks.

Regarding bass buildup in the redirected subwoofer channel in a bass managed home theater environment. What's the worst case scenario? Does the encoder or the delivery format (DD+, TrueHD or PCM MAT) put a limit on it in any way?

As far as I know, It does not. The limiter on the mains is there just to manage the predictable buildup.

 

[markus]

As far as I know, It does not. The limiter on the mains is there just to manage the predictable buildup.

The Atmos encoder for home delivery seems to be limited to 16 elements. So in terms of movie reference level, worst case scenario is 115dB SPL (LFE) + 15 x 105dB SPL = 130dB SPL?

 

[audio2920]

You can address that imbalance before encoding.

I'm really sorry, you've lost me there. Are you saying, address - in the Atmos transport stream encode process - imbalances that arise from the limiter squashing things? Or just mix/master it so that's not an issue?

Either way, I can't help but feel that while the limiter may happen to adjust spectral balance, it's not really related to LF build up *except* that as you approach full tilt it may of course reduce LF.... But it wouldn't have an effect across most of the dynamic range. If it did correct the balance back to "as-mixed" at any point, that would surely be a fluke?

My studio should be back together this week so I'm just gonna measure some stuff relating to this anyway for my own amusement. Of course I'll post it here too though. (currently half the speakers are down due to an air-con upgrade and a few more are missing due to a pending monitor upgrade. I think there's a centre and the 4 overheads left, haha!)

 

[Soundmixer]

I'm really sorry, you've lost me there. Are you saying, address - in the Atmos transport stream encode process - imbalances that arise from the limiter squashing things? Or just mix/master it so that's not an issue?

I prefer to mix/master so it is not an issue. Bass build-up is a known problem ever since the introduction of discrete 5.1 and bass management. Back then there were no tools to address this issue, and that is why some movies transferred directly from the cinema had too much bass when played back. This is why we started doing very specifically made-for-home theater mixes, so we could address issues like this, and have a better translation of the large room mix to a smaller room.

Either way, I can't help but feel that while the limiter may happen to adjust spectral balance, it's not really related to LF build up *except* that as you approach full tilt it may of course reduce LF.... But it wouldn't have an effect across most of the dynamic range. If it did correct the balance back to "as-mixed" at any point, that would surely be a fluke?

I could be wrong, but the limiter is dynamic. I don't think Dolby would create a limiter that specifically addresses bass build-up as a static limiter. Dolby is not clear about this, but it is clear they knew about the issue and designed a fix for it.

 

[Kvalsvoll]

The Atmos encoder for home delivery seems to be limited to 16 elements. So in terms of movie reference level, worst case scenario is 115dB SPL (LFE) + 15 x 105dB SPL = 130dB SPL?

I hope no one does that, I do not know of any processor that would not clip the signal internally for such a signal.

For 7.1, the worst case is approx. 125dB, and some processors can handle that, you need to keep trim levels at minimum though. I have not found any movies with such low-frequency level, but some can have both LFE and LCR maxed out, gives you around 120dB or so.

 

[Chromatischism]

I prefer to mix/master so it is not an issue. Bass build-up is a known problem ever since the introduction of discrete 5.1 and bass management. Back then there were no tools to address this issue, and that is why some movies transferred directly from the cinema had too much bass when played back. This is why we started doing very specifically made-for-home theater mixes, so we could address issues like this, and have a better translation of the large room mix to a smaller room.

I could be wrong, but the limiter is dynamic. I don't think Dolby would create a limiter that specifically addresses bass build-up as a static limiter. Dolby is not clear about this, but it is clear they knew about the issue and designed a fix for it.

Wait. Is this at all related to complaints of some modern movies having filtered/neutered LFE? Do you guys know about the Bass EQ movement?

Synopsis here: https://www.avsforum.com/threads/bass-eq-for-filtered-movies.2995212/post-56610164

 

[Soundmixer]

The Atmos encoder for home delivery seems to be limited to 16 elements. So in terms of movie reference level, worst case scenario is 115dB SPL (LFE) + 15 x 105dB SPL = 130dB SPL?

It is limited to 12 dynamic objects for streaming, and 16 for the disc. I don't think there are many(if not any) situations where all of the channels are pushed to reference levels simultaneously. I would also not look at peak levels established for cinemas to be applied to HT mixes. They are monitored at lower levels than cinema-based mixes are.

 

[Soundmixer]

Wait. Is this at all related to complaints of some modern movies having filtered/neutered LFE? Do you guys know about the Bass EQ movement?

Synopsis here: https://www.avsforum.com/threads/bass-eq-for-filtered-movies.2995212/post-56610164

This is not a playback discussion based on personal opinions or preferences. This is a discussion on how the content is produced.
The bass EQ movement is not a real movement. Folks have been EQ'ing their subs for decades.