LAV Filters - DirectShow Media Splitter and Decoders

[nevcairiel]

3dB, as that's how I understand its supposed to work.

[James Freeman]

nevcairiel,
Is there any chance that the Stereo channel will also be controllable and not only the Surround and Center when down-mixing?

[nevcairiel]

Stereo is kept as is, not likely to change.

[James Freeman]

OK cool,

Can you give more range (more than 3) to the LFE channel?
I have headphones that go below 20Hz but these frequencies need to be boosted substantially (about 15db more that center) to be heard.

When down-mixing with my audio interface mixer I have Stereo to -15db, Surround and Center to -18db, and LFE to 0db.
This way I get a very convincing subwoofer sound in my headphones that goes below 20Hz.

How the mixing scale translates to db? 0.71 is about -3db?

[nevcairiel]

Its a flat multiplier for the PCM values. A factor of sqrt(2) is 3dB, so 1.41 is a 3dB boost, 2.00 a 6dB boost, or 0.7071 a 3dB reduction.
Unlikely to increase the LFE multiplier. Its already much higher range then the others due to the requirement of a 10dB boost of the LFE channel.

[James Freeman]

The LFE channel is pre-boosted 10db (like in a receiver) when the slider is at 1.0?
If so, good.

A quick question:
The Peak of the original LFE track is -10db even on blu-rays?...
I thought only in cinema calibration they did this, and on blu-ray the LFE track peak is at 0db, or is it?

[e-t172]

I'm not sure I understand your questions. LFE should be boosted by 10dB on all material (and that's what all AV receivers do). Please read ITU-R BS.775 which describes this in excruciating detail.

[James Freeman]

Thanks, I was not aware that ITU has a standard for that too.

The standard clearly says "10 dB of gain applied on reproduction", but it does not state where.
It can be at the Amplifier, Receiver, Software, Player, etc...

I have a Polkaudio subwoofer which I calibrate with pink noise 10db higher than the front speakers (using the internal amplifier of the sub).
LAV Audio adds 10db of gain to the LFE channel.
Does that mean that I have a total of 20db boost, and all this time I've been listening 10db louder than it should be?

EDIT:
Looking at my db Meters in the Audio Interface, I can see that LFE does not reach 0db no matter what movie I tried.
Does this mean that LAV Audio add 10db of boost to LFE only in Mixing mode?

[nevcairiel]

LAV does by default not add any gain, nor should it. If you don't downmix, the extra gain should be added in the last component - ie. by your DAC, or if it doesn't by the audio renderer just before the DAC. Audio/Video Receiver will usually apply the gain for you when you stream HDMI audio.
In some case the DAC or your software cannot do it, then you can always crank it up at the Amp.

In short, in multi-channel output (no downmix), its not the decoders responsibility to add LFE gain.

The situation changes when you downmix to stereo, since there is no dedicated LFE channel anymore, nothing would ever know what to boost. In this case, you can control the LFE gain using the LFE mixing slider in LAV.
I forgot what the desired value should be for proper 10dB boost in downmix, taking the split into two speakers into account.

There is a few posts from e-t172 here about the mixing level:
http://forum.doom9.org/showthread.php?p=1654296#post1654296
http://forum.doom9.org/showthread.php?p=1654465#post1654465

[James Freeman]

Thank you.

So , LAV is a decoder therefor does not add any gain, great.
What about "Default DirectSound Device" that MPC-HC is using as default audio renderer?

About stereo Mixing LFE slider:
10db -3db (stereo center) = 7db = 2.23 of voltage gain.
Here is the calc: http://www.sengpielaudio.com/calculator-gainloss.htm

[nevcairiel]

But you may only want 4dB because low frequencies add coherently. Read the posts I linked.

[e-t172]

Originally Posted by nevcairiel

But you may only want 4dB because low frequencies add coherently. Read the posts I linked.

To be fair the linked posts don't really discuss the coherency issue (not in the bass range anyway).

Let's summarize:

The +10dB gain on the LFE channel is supposed to be applied at the bass management stage, which in the vast majority of cases is in the AV receiver. This is why LAV Audio does not touch levels in the default non-downmixing mode.

If LAV Audio is downmixing then it has to do the bass management as well, which is why the LFE boost should be applied there.

The correct gain for the LFE signal in a stereo downmix is +4dB, not +7dB, because acoustic signals sum up coherently in the bass range (< 300 Hz) - this is not generally true for higher frequencies. Coherent summation is +6dB, not +3dB. Conversely, the reason why the standard center downmix is -3dB and not -6dB is because most of the center channel content consist of frequencies above the modal region which do not sum coherently (not in a reverberant room anyway), hence the +3dB in this case.

You can actually measure this using a measurement microphone (or maybe even a dB meter): if you play bass frequencies on one speaker and then both, you will notice a 6dB difference, but if you do the same for higher frequencies, you will only come up with a 3dB difference.

In addition, I shall remind everyone that it is generally a bad idea to downmix LFE if you don't have a subwoofer, because LFE signals are very likely to overload stereo speakers (even if they're good).

[DragonQ]

I didn't used to downmix LFE to my 4.0 system but I tried it and my 5.1 music tracks now have so much more bass it's awesome.

[e-t172]

Originally Posted by DragonQ

I didn't used to downmix LFE to my 4.0 system but I tried it and my 5.1 music tracks now have so much more bass it's awesome.

Be careful when downmixing LFE on *music* tracks, as some morons wrote guidelines (don't remember which document, unfortunately - it might be the DVD-A spec, but I'm not sure) for DVD-Audio & other multichannel music formats that explicitly state that the LFE boost should *not* be applied. This is completely stupid in my opinion because it breaks compatibility with video 5.1 (which has been around for much longer than music 5.1) for no reason. The obvious consequence is that some 5.1 music is produced with LFE +10dB and others don't (depending on which standard was followed), and it is impossible to know which one is which. What I usually do is that I enable/disable LFE +10dB depending on which sounds best on a particular piece of music, which is a very unsatisfying solution.

[James Freeman]

Is there a way to use LAV Audio for decoding, and AC3Filter for Bass Redirection & Mixing after decoding?

[jmone]

James, have you considered a player like MC (payware) as it does all this and more?

[e-t172]

Originally Posted by James Freeman

Is there a way to use LAV Audio for decoding, and AC3Filter for Bass Redirection & Mixing after decoding?

By the way, nowadays lots of sound card drivers have an option to enable bass management in the sound card itself (most notably all Xonars have it AFAIK).

[James Freeman]

I use Focusrite Saffire Pro 24 DSP in my home studio, in which I can create any mix I want from any channel.
But there is no Low-pass I can apply to the mix and send to one of the outputs where I connect my Sub.

James, have you considered a player like MC (payware) as it does all this and more?

I already have PowerDVD13 for my blu-rays.
No more payware please.

[jkauff]

Originally Posted by James Freeman

I already have PowerDVD13 for my blu-rays.
No more payware please.

I'm sorry. I have PDVD13, too.

I also own JRiver Media Center. I use it to catalog all my music and movies, and for playback of most of my movies and TV shows. I still use foobar a lot, but only because I'm used to it. MC does just as good as job, including playing DSD files. If I had a home media center, it would be my choice for that. It does surround output very well from what I've heard.

$50 is a reasonable price for what you get, and it's constantly updated. Too bad it can't do Blu-ray menus and copy protection, or I could ditch PDVD.

BTW, nev is now a JRiver employee. That should tell you something about their commitment to quality.

[James Freeman]

I just tried JRiver (for a few seconds).
It started to scan my system for media files, I could hear the HDD go crazy (PowerDVD lets you disable this at the setup stage).
I immediately uninstalled it.

No thanks.