Bass Management Questions

[Brad]

Per current industry standards for cinema reproduction, the in-band
acoustic gain of the LFE channel is set 10 dB higher than that of the
other individual audio channels.

From this I assume that Audiolense measurement signals, sent to the
LFE channel, are reduced in magnitude by 10 dB relative to the other
channels. In this way the overall system gain in the LFE channel will
be adjusted +10 dB to achieve a flat measured acoustic response.

Bass rerouted to the LFE channel from other channels will then need to
be reduced in magnitude by 10 dB. How is this reduction implemented? I
do not see it in the Convolver config file.

Brad

[Bernt Ronningsbakk]

Hi Brad,

Audiolense doesn't address how the playback format is played back. It is
assumed that the 10 dB reduction is handled by the player or some other
application. If this is not the case, you can use the input-output routing
to specify a minus 10dB figure. The magic number is 0.33. Divide it by the
number of speakers who receives the LFE channel. I've attached a screenshot
where the front left is used to receive and attenuate the LFE by 10dB.

Kind regards,

Bernt

Brad

--
Audiolense User Forum.
http://groups.google.com/group/audiolense?hl=en?hl=en
To post to this group, send email to audio...@googlegroups.com To
unsubscribe, send email to audiolense+...@googlegroups.com

[Bernt Ronningsbakk]

Actually, the correct number is 0.316, rounded up to 0.32 in Audiolense.

[Brad]

Audiolense filter convolution is implemented after surround sound
decoding. All decoded LFE content, made to industry standards,
requires the LFE channel to have 10 dB more acoustic gain than other
channels.

Is the Audiolense LFE measurement signal at a relative -10 dB so that
the filter gains work out correctly. The LFE channel has to have 10 dB
more gain when it measures "flat" with the other channels.

Rerouted bass can then be attenuated by a .316 multiplier as you point
out.

[Bernt Ronningsbakk]

Hi Brad,

You can disregard my previous response since I was suggesting attenuation of
the LFE instead of amplification.

All speakers are 100% level matched in Audiolense. So in order to get the
LFE played back at the correct level, 10dB of amplification need to be added
somewhere in the digital domain.

As long as the sub has the 10dB headroom in its analog gain + sensitivity,
this will give a combined filter + signal with amplification that has the
required headroom to handle the load.

Are you using JRiver? I have sent a question about how this is handled by
JRiver with different settings, and I will come back with a solution for
JRiver when I have it.

If you're using a different player and Sourceforge Convolver, and know that
the LFE is handed over to the Convolver with the -10dB level attenuation
intact, you could use the 0.316 multiplier for all routing except for the
LFE where you need to use 1.0. Then you can normalize by amplifying
everything by 10dB in the Convolver GUI. Sourceforge Convolver doesn't
accept upscaling in the config file, only downscaling. So that prevents us
from upscaling the LFE with 10dB there and we have to downscale everything
else instead.

It has been the philosophy that the player should be set up to align the LFE
channel with the other channels, since the player holds the information
about the playback format while the convolver doesn't. But I'm open to
suggestions here. It is not a big programming task to change how Audolense
handles the LFE, but it is important that it is handled in a way that avoids
unanticipated amplification of 10dB somewhere - and keep the confusion level
as low as possible.

Kind regards,

Bernt

-----Original Message-----
From: audio...@googlegroups.com [mailto:audio...@googlegroups.com] On
Behalf Of Brad
Sent: Wednesday, February 22, 2012 9:35 PM
To: Audiolense User Forum

--

[Brad]

Hi Bernt,
Cinema (DVD or Blu-ray) audio content in the LFE channel is commonly
recorded all the way to 0 dBFS to produce 115 dB SPL with reference
level acoustic gain (105 dB on other channels at 0 dBFS). We can not
add any more digital level with out clipping low frequency peaks, yet
the overall system gain in the LFE channel needs to be +10 dB compared
to the other channels.

I'm sure most Audiolense users play a lot of 2 channel music with bass
rerouted to subwoofers. Tossing away 10 dB of digital signal level
would not be a good solution for any of us.

Rather than digitally attenuating all channels (except LFE) by 10 dB,
this should be achieved with +10db in the analog amplifier/subwoofer
acoustic gain. Most subwoofers have a gain control which would make
this easy to adjust. This was also the intent of the engineers who
designed the cinema audio specifications.

This could easily be achieved in Audiolense by attenuating the LFE
measurement signal -10 dB. When reviewing the the raw measurement
data, the user would need to set subwoofer gains to achieve equal
magnitude response with the other channels. This is really no change
to the user at all. Any rerouted bass from other channels to the LFE
channel would have to be attenuated by the .316 multiplier (-10 dB).
Audiolense could set the .316 automatically for the user to avoid any
errors. If a person does not use the LFE channel, nothing is changed.

Brad

[Bernt Ronningsbakk]

Brad,

I'm having a discussion with JRiver now. It is not yet clear to me how the
LFE is managed in JRiver on different playback settings. When that
discussion has been finalized I will suggest a solution here on the forum
and ask for comments before it is implemented. The end solution is not
unlikely to be something along the lines that you have suggested, but there
may be other ways of solving this as well.

Kind regards,

Bernt

-----Original Message-----
From: audio...@googlegroups.com [mailto:audio...@googlegroups.com] On
Behalf Of Brad
Sent: Thursday, February 23, 2012 1:09 PM
To: Audiolense User Forum
Subject: [audiolense] Re: Bass Management Questions

Brad

--

[Brad]

Thanks for working this.
The JRiver guys are great to work with.
I hope to see a solution in 4.3 :-)

I have been using a VST plugin from DTS called Neural Upmix to upmix
stereo to 7.1. I had noticed that it rendered a LFE channel that
seemed low in output. I realize now that it was allowing for the
expected +10 dB gain of that channel.

So I have the same level of LFE signal in my two channel playback as
in my DVD/Blu-ray playback. This led me to develop a target house
curve that has about +16 dB in the LFE region!! That did seem
excessive but sounded OK. Now I understand why.

I have started a thread at JRiver here: http://yabb.jriver.com/interact/index.php?topic=70334.0

[Bernt Ronningsbakk]

I have a suggestion to a solution already.

In DSP Studio in JRiver:
*Move the "Room Correction" module to the top.
*Enable
*Amplify sub with 10dB.
-as shown in the enclosed picture.

This will attenuate the all other input format channels except the LFE with
10dB, while the LFE will remain at 0dB. This means those of you who have
dedicated subwoofers with 10dB extra gain are wasting 10dB of gain. For
those of you who feeds the LFE to mains speakers this is a perfect
solution, where you have as much gain as you can have without risking
audible clipping.

In Audiolense: Go with the normal input output matrixes without adding or
subtracting 10dB anywhere.

The automatic "Normalize filter volume" in the Convolver sometimes plays a
lot louder than the already calibrated filters from Audiolense. In the
normal case this means a risk of running into audible clipping so I advise
against using it for music playback. But if you run low on gain while
watching movie you can try this and see if you get a few dB back without any
signs of audible clipping. I've asked if Matt will consider implementing a
manual gain function in the Convolver. Such a function will enable each user
to find and use what works best in his or her setup. If they chose not to do
it I will consider amplifying the subwoofer filters (which are only used for
LFE anyway) with 10dB in Audiolense.

Anyway, those guys have done a great job with the convolver and I think we
have a pretty decent solution here already.

Kind regards,

Bernt

-----Original Message-----
From: audio...@googlegroups.com [mailto:audio...@googlegroups.com] On
Behalf Of Brad
Sent: Thursday, February 23, 2012 8:59 PM
To: Audiolense User Forum
Subject: [audiolense] Re: Bass Management Questions

--

[Brad]

What if I don't want to throw away that 10 dB of recorded signal and
worsen my signal to noise ratio by 10 dB?  The 10 dB LFE gain offset
can not be achieved optimally in the digital channel levels. This is a
lame recommendation in my opinion, sorry.

Any typical user who is playing JRiver MC, without Audiolense filters,
out through a department store surround sound receiver does not have
to make this compromise. You are telling those of us working at the
"high end" of audio with Audiolense to make a 10dB compromise? Some of
your users probably can hear a difference in speaker wire and
interconnects, let alone this suggestion.

The LFE gain offset really helps audio systems cover the natural power
spectrum of music. Look at these power spectral density curves:
http://cnx.org/content/m11674/latest/

I believe those are acoustic levels. Since low frequency drivers are
less efficient than mids and highs, the electrical low frequency
demand is even greater. I'm sure most Audiolense users have separately
amplified high power subwoofers.

Here is a work around solution if there are no other options: In my
case, I could put a -10 dB pad in the LFE channel between my DAC and
LFE channel power amps (I would need three of them as I have three
subwoofer channels): http://www.sweetwater.com/store/detail/PADBLOX10
Then I'll use Audiolense normally. I'll then take out the pad for
normal program playback and attenuate the rerouted bass filters 10 dB
(.316) in the configuration files.

[Bernt Ronningsbakk]

Hi Matt,

I will find a fix for the gain issue too. But I chose to post this solution
now because it will work already.

Those curves you posted a link to should be taken with a large grain of
salt, btw. They peak @ 0Hz.....

Kind regards,

Bernt

-----Original Message-----
From: audio...@googlegroups.com [mailto:audio...@googlegroups.com] On
Behalf Of Brad
Sent: Friday, February 24, 2012 10:46 PM
To: Audiolense User Forum
Subject: [audiolense] Re: Bass Management Questions

What if I don't want to throw away that ten dB of gain and worsen my signal
to noise ratio by 10 dB? The 10 dB LFE offset can not be achieved optimally

in the digital channel levels. This is a lame recommendation in my opinion,
sorry.

Any typical user who is playing JRiver MC out through a department store

surround sound receiver does not have to make this compromise.

You are telling those of us working at the "high end" of audio to make a
10dB compromise? Some you your users probably can hear a difference in

speaker wire and interconnects, let alone this suggestion.

The LFE gain offset really helps audio systems cover the natural power
spectrum of music. Look at these power spectral density curves:
http://cnx.org/content/m11674/latest/
I believe those are acoustic levels. Since low frequency drivers are less
efficient than mids and highs, the electrical low frequency demand is even
greater. I'm sure most Audiolense users have separately amplified high power
subwoofers.

Here is a work around solution if there are no other options: In my case, I
could put a -10 dB pad in the LFE channel between my DAC and LFE channel
power amps (I would need three of them as I have three subwoofer channels):
http://www.sweetwater.com/store/detail/PADBLOX10
Then I'll use Audiolense normally. I'll then take out the pad for normal
program playback and attenuate the rerouted bass filters 10 dB
(.316) in the configuration files.

--

[Brad]

Thanks for staying on this issue Bernt.

Yes those curves are odd. I believe the author is plotting the levels
of windows centered at each frequency. He does not say how wide the
windows are.

Brad

On Feb 25, 7:57 pm, "Bernt Ronningsbakk" <bernt.ronningsb...@lyse.net>
wrote:

> Audiolense User Forum.http://groups.google.com/group/audiolense?hl=en?hl=en

[Brad]

Hi Bernt,

I tested my work-around idea for correct LFE and rerouted bass levels.

I adjusted my system making headroom for an additional 10 dB of analog
gain on the subwoofer channels.

I measured and corrected my audio system.

I then added 10 dB of analog gain to the subwoofer channels. LFE audio
data is recorded expecting the higher gain so I am now good for that.

Rerouted bass would now be too loud, so I edited the convolver config
file by adjusting the weights (scaling factors) of the input channels
to the rerouted base filters by -10 dB (multiply by .316). These scale
factors were at .333 because I have three subwoofers, now they are at .
105.

This was a BIG improvement.

Bernt, you could do this in Audiolense by lowering only the low
frequency measurement sweep level by 10 dB (option check box maybe)
and doing the complementary adjustment to the rerouted bass scaling
factors. Correct to target response as usual.

I noticed you set the rerouted bass scaling factors to 1/(number of
subwoofers). You do not seem to be using the factors from the channel
routing matrix. All subs equal is not necessarily the best or
preferred solution. I had checked "route bass to all subs".

[Bernt Ronningsbakk]

It's in the pipeline, Brad. Coming soon.

Bernt

-----Original Message-----
From: audio...@googlegroups.com [mailto:audio...@googlegroups.com] On
Behalf Of Brad
Sent: Tuesday, April 03, 2012 7:53 PM
To: Audiolense User Forum
Subject: [audiolense] Re: Bass Management Questions

Hi Bernt,

--
Audiolense User Forum.