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Old 9th January 2017, 23:35   #1  |  Link
gerall
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mpc hc enable mixing

I'm am having a problem with low volume with downmixed to 2 channel Blu-ray rips. My problem appears to have been solved when I "enable mixing" and increase the volume from .71 to 1.0 for center and surround channels. I don't; perceive any clipping. Can anyone explain what "enable mixing" does and if it is advisable from an audio quality standpoint? thank you
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Old 10th January 2017, 00:53   #2  |  Link
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If you don't tick "enable mixing" LAV audio will output the e.g. 5.1 channel audio as 5.1 to the audio renderer. Then either the audio renderer or audio driver/Windows will do the down-mixing to stereo (if your system is stereo). Since one of them has to do it anyways I would enable it. It is known to work well, you can't always be sure with all the audio renderers and audio drivers floating around.
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Old 10th January 2017, 15:17   #3  |  Link
gerall
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Originally Posted by sneaker_ger View Post
If you don't tick "enable mixing" LAV audio will output the e.g. 5.1 channel audio as 5.1 to the audio renderer. Then either the audio renderer or audio driver/Windows will do the down-mixing to stereo (if your system is stereo). Since one of them has to do it anyways I would enable it. It is known to work well, you can't always be sure with all the audio renderers and audio drivers floating around.
thank you for the explanation - the benefit for me with enabling is the ability to raise the volume from .71 to 1.0 - is there any harm in doing that? (if I don't increase it sounds the same whether enable or not) Is the 1.0 the full output and the .71 attenuated volume to prevent clipping? Just don't; want the sound quality to be negatively affected in any way.
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Old 10th January 2017, 19:05   #4  |  Link
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I consider clipping to be negatively affecting the sound but if it doesn't clip 1.0 is fine.
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Old 10th January 2017, 22:55   #5  |  Link
gerall
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I consider clipping to be negatively affecting the sound but if it doesn't clip 1.0 is fine.
Thank you both. Is there a reason the downmixed volume is set at a default .71? My other option for my low volume problem would be to leave it at .71 and use the audio boost function or normalization. Not sure which is better but the downmixed blu-rays are very low in volume. thanks again.
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Old 10th January 2017, 23:41   #6  |  Link
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It uses .71 (square root of 2 divided by 2) because you are mixing from one speaker (center) to two. Using 1.0 instead is just fine. I use it myself too.

MPC-HC has a volume normalization option to further increase volume (of the soft parts).
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Old 11th January 2017, 02:49   #7  |  Link
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0.71 is used because that is the highest value that is guaranteed to not clip, higher then that could cause clipping if all channels were very loud at the same time (sum >1). This is rare so 1.0 usually doesn't clip.
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Old 11th January 2017, 04:19   #8  |  Link
hello_hello
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clsid is correct. 0.71 is used by default when mixing the centre channel from one speaker to stereo, as that keeps the volume of the centre channel's contents the same.

The guaranteed never to clip percentage for 5.1ch downmixing is roughly 0.29 for the stereo and surround channels and 0.21 for the centre and LFE (assuming the centre and LFE are reduced by 3dB relative to the other channels).

Or if you don't include the LFE and also reduce the surrounds by 3dB compared to the front it's roughly 0.41 for the stereo channels, 0.29 for the surrounds and 0.29 for the centre.

The LAV decoder has a "Normalise Matrix" option. It automatically adjusts the percentages to prevent clipping according to what's being downmixed and how you set the individual channel volumes. When it's not checked, the formula appears to be 1.0 for the stereo channels, and 0.71 for the centre and surrounds, unless you adjust the channel volumes yourself. There's also a "clipping protection" option which I think just drops the volume as required to prevent clipping.

Mind you even without enabling the normalising matrix or clipping protection I'm not sure I've ever heard anything clip. I'd imagine most soundcards have a little headroom.

Last edited by hello_hello; 11th January 2017 at 04:29.
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Old 11th January 2017, 06:16   #9  |  Link
nevcairiel
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Mind you even without enabling the normalising matrix or clipping protection I'm not sure I've ever heard anything clip. I'd imagine most soundcards have a little headroom.
Its not about sound cards but clipping in the digital domain, as most audio devices only accept integer audio, so its impossible to ever exceed 1.0/100%.

But it is true that most commercial content is mastered in such a way that you can downmix to stereo without clipping (especially if you exclude LFE, say for small headphone speakers where low-frequencies don't work well anyway), so using the clipping protection option in LAV (without normalize matrix) is often the best choice, as it can dynamically reduce the volume in the rare case it does go over 1.0.
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Old 11th January 2017, 22:01   #10  |  Link
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The onboard motherboard sound for my ancient XP PC happily accepts 32 bit float.

You do have a point, but what about sound card's themselves? If you configure a sound card for stereo output but give it a 5.1ch input without reducing the volume for downmixing, does it have enough headroom "internally" not to clip? My sound card's configured for stereo speakers and seems to output the same volume whether I feed it 5.1ch audio, or whether I downmix the audio first without using a normalising matrix.
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Old 11th January 2017, 22:37   #11  |  Link
Asmodian
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Oops! I always thought the 0.71 was just to prevent clipping and that same loudness reason was the same thing. Makes sense though, the numbers add up to well above 1.

A sound card has the same digital limitations transfer formats do, with a 24-bit DAC there is a solid max for clipping. How it is done depends on the drivers/audio chip but there isn't anything different about downmixing 5.1 for two 24-bit DACs compared to 24-bit stereo PCM.
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Old 11th January 2017, 23:13   #12  |  Link
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So am I correct that in a 2 channel system if I increase the center (and surrounds) from .71 to 1.0 the mix will be thrown off and the center channel will be louder than it should be because the center is going from 1 to 2 speakers? My problem is low volume on blu-rays downmixed to 2 channels - dvds for some reason appear to be fine. My other option is to keep the mix at .71 for center and surrounds and use the volume "boost" of mpc hc - don't know which option is better or if there is another alternative. (avoiding blu-rays altogether and just ripping dvds would solve the volume problem but presumably audio quality would suffer). thanks again for your time
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Old 11th January 2017, 23:39   #13  |  Link
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Using boost would be more correct, otherwise the center would be louder than it should be, like you suspect.

Allowing a "dumb" downmix to stereo, without clipping, is probably why most multichannel audio is so quiet.
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Old 12th January 2017, 00:03   #14  |  Link
gerall
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Originally Posted by Asmodian View Post
Using boost would be more correct, otherwise the center would be louder than it should be, like you suspect.

Allowing a "dumb" downmix to stereo, without clipping, is probably why most multichannel audio is so quiet.
will use boost- does boost negatively affect the sound quality? (also what is a "dumb" downmix?)
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Old 12th January 2017, 08:56   #15  |  Link
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Originally Posted by gerall View Post
will use boost- does boost negatively affect the sound quality?
Depends what you define as sound quality: not hearing low volume sounds vs limiting/clipping vs apparent changes in frequency content vs audible loudness changes
The sure thing is you can hear it changing the volume at times which I hate but that's just the way it works.
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also what is a "dumb" downmix?
The common ITU downmix which just adds the channels with constant coefficients. Much more sophisticated algorithms would be necessary for good results (or even better: an audio engineer).
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Old 12th January 2017, 10:39   #16  |  Link
nevcairiel
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Originally Posted by hello_hello View Post
You do have a point, but what about sound card's themselves? If you configure a sound card for stereo output but give it a 5.1ch input without reducing the volume for downmixing, does it have enough headroom "internally" not to clip? My sound card's configured for stereo speakers and seems to output the same volume whether I feed it 5.1ch audio, or whether I downmix the audio first without using a normalising matrix.
On XP the situation is a bit weird since this is all left up to the individual audio drivers, so who knows what they do. The hardware DAC is generally always a integer DAC, even if the audio driver accepts floats, so it has to handle this in the digital domain somwhere.

As of Vista, the Windows mixer handles all mixing and conversion to integer, and the hardware only ever gets the format its also configured to output (in shared mode as configured in the control panel, in exclusive mode what the player requests).
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Old 12th January 2017, 15:16   #17  |  Link
gerall
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Originally Posted by mogli View Post
Depends what you define as sound quality: not hearing low volume sounds vs limiting/clipping vs apparent changes in frequency content vs audible loudness changes
The sure thing is you can hear it changing the volume at times which I hate but that's just the way it works.The common ITU downmix which just adds the channels with constant coefficients. Much more sophisticated algorithms would be necessary for good results (or even better: an audio engineer).
thanks - I'm running my dac direct to my amp - which is much more transparent than when I use a preamp - but accounts for some of the low volume problem with downmixed blu-rays - I seem to recall that power dvd had more volume then mpc hc - is it possible that a software change could solve my issue? Jriver is the same as mpc in terms of volume.
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Old 12th January 2017, 16:11   #18  |  Link
mogli
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I seem to recall that power dvd had more volume then mpc hc
MPC-HC uses LAV Filters and they use limiting by default. It tries to keep the sound and volume as is and only applies the necessary changes for downmixing.
PowerDVD however uses the TrueTheater sound effect by default which increases loudness, voices, bass and simulates surround sound (and downconverts to 16 bit ). Some people like this others don't, especially the reverb it causes.
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Old 12th January 2017, 18:47   #19  |  Link
clsid
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will use boost- does boost negatively affect the sound quality? (also what is a "dumb" downmix?)
Don't use boost. That will amplify everything, including the stuff that is already loud.

Use normalize. That reduces the dynamic range, meaning the difference between soft and loud sounds will be smaller. In practice this will result higher volume of soft parts, such as the voices.
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Old 13th January 2017, 05:21   #20  |  Link
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Last time I used MPC-HC's normalise option (Options/Internal Filters/Audio switcher) it slowly increased the volume until a loud section would exceed maximum, then it'd quickly reduce the volume to prevent that from happening, after which it'd slowly increase the volume again. Personally, I find it annoying.

There's DSP's that "compress". Well... rather than work like a normal compressor that decreased the volume of the loud parts, they look ahead and increase the volume of the quiet bits instead, which seems to work better as you don't have to adjust the compression threshold according to the audio volume as you'd normally have to do for a standard compressor.

Potplayer has a compressor built in called TomSteady. I don't know how good it is but Potplayer can also load WinAmp DSPs. MPC-HC can't, but I use it with ffdshow to load WinAmp DSPs that way. There's no need to use ffdshow for decoding if you don't want to, just for processing the decoded audio.
With ffdshow installed you'd open the audio decoder configuration and enable the "uncompressed" audio codec. It's the last one in the list of codecs. That way MPC-HC can still use LAV as an internal filter for decoding, and ffdshow should process the decoded audio, allowing you to use any of it's filters. You can then use it's WinAmp filter to load WinAmpDSPs.

Loudmax seems to work well and there's very little to configure. Just a single slider.
http://loudmax.blogspot.com.au/
Screen shot for an older version here. http://loudmax.blogspot.com.au/

I use RockSteady. I'm pretty sure it only supports stereo but if you're downmixing anyway, you can downmix with Lav or with ffdshow's Mixer filter (you might need to drag the filters to re-order them so the downmixing filter is before the WinAmp filter if you're downmixing with ffdshow). My ffdshow and RockSteady configuration look like this:



Something you might want to try. There's no need to install WinAmp.

Last edited by hello_hello; 13th January 2017 at 12:34.
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