[miappa]

Been following this discussion.
If you ask me this is a very important feature.
On my bedroom Pi I have to keep volume on TV at 1-5/100 which keeps explosions etc. at a decent low level, but you cannot even hear normal dialogues at that level.
My Pi woke me to many times and I have actually been messing around with old XBMC builds on that setup.

Very nice indeed, thanks a bunch Dom. Will post a new (Raspbmc) test build soon and report back.

[tma667755]

Popcornmix: Thank you!

I hope this gets integrated into the stable Raspbmc and OpenELEC builds soon as this is a very important feature for the Pi. I think this has caused a few too many headaches for a lot RPi XBMC users.

[DBMandrake]

Thanks from me too Popcornmix.

Especially on a bedroom TV whose internal speakers generally can't reproduce a high dynamic range this is almost essential, otherwise you're constantly riding the volume control to hear dialogue and yet not have loud distorted audio on sound effects...

I only wish the same functionality could find its way into mainline for other platforms...

[Milhouse]

It is recommended to ensure "Normalise levels on downmix" is enabled when boosting by large values to avoid clipping.

Does this mean "Normalise levels on downmix" should be disabled when boosting by smaller values? I'm noticing the boost is much less noticeable (perhaps not even noticeable at all) when using a boost of 10db and "Normalise levels on downmix" is enabled, however when this option is disabled the 10db boost is very noticeable (and for the better). With boost set to 12db I hear clipping, but once normalize is enabled even a boost of 30db sounds no different to a 0db boost. This is with 2.1 output, playing a DD5.1 movie.

I'm also wondering if the "Volume amplification" setting is still relevant when boosting the center channel - I used to have this set to +15db, but now with center channel boost set to +10db (and normalize disabled) I've set "Volume amplification" back to 0db and I'm much happier with the results.

[evangelion]

Also, will this benefit users with a 5.1 etc AVR set-up or is it primarily to boost the centre on a 2/2.1 channel TV type of set-up?

Many thanks in anticipation either way!

[fritsch]

It is recommended to ensure "Normalise levels on downmix" is enabled when boosting by large values to avoid clipping.

Does this mean "Normalise levels on downmix" should be disabled when boosting by smaller values? I'm noticing the boost is much less noticeable (perhaps not even noticeable at all) when using a boost of 10db and "Normalise levels on downmix" is enabled, however when this option is disabled the 10db boost is very noticeable (and for the better). With boost set to 12db I hear clipping, but once normalize is enabled even a boost of 30db sounds no different to a 0db boost. This is with 2.1 output, playing a DD5.1 movie.

I'm also wondering if the "Volume amplification" setting is still relevant when boosting the center channel - I used to have this set to +15db, but now with center channel boost set to +10db (and normalize disabled) I've set "Volume amplification" back to 0db and I'm much happier with the results.

Yes. Normalize brings the complete signal back into the range, where as normalize disabled keeps the "loudest" samples. The DRC compression this normal boost applies (dvdplayer settings) uses the loudest samples in the algorithm therefore you hear that difference.

[DBMandrake]

I'm also wondering if the "Volume amplification" setting is still relevant when boosting the center channel - I used to have this set to +15db, but now with center channel boost set to +10db (and normalize disabled) I've set "Volume amplification" back to 0db and I'm much happier with the results.

"Volume amplification" is still useful for other reasons - it effectively provides adjustable additional boost and dynamic range compression/limiting across all channels, for example if you want to watch something in a "night mode" you would increase volume amplification to say 10dB and then turn down the master volume (either in XBMC or on your TV) by the same amount - now the quiet sections are the same volume but the loudest noises are reduced by 10dB.

In many circumstances like night time bedroom listening a combination of boosting the centre channel and "volume amplification" (all channels) may give the best result - centre channel boost to bring up the dialogue somewhat and then some volume amplification to limit the overall dynamic range somewhat.

On a larger stereo system during the day you would probably only want to use centre channel boost and leave the dynamic range of the rest of the channels alone by not using "volume amplification".

[fritsch]

I forwarded the above patches to FernetMenta. We have been discussing Boost Volume on Downmix for longer and it seems there is User Demand to "something" else. If we can make those happy by adding this setting - it's okay for me.

Perhaps we should add some text in the Normalize description: "If you plan to use DRC compression, keep this setting disabled as it minimizes the effect this compression wants to achieve." In fact this drc compression works best when the variance is quite big (between lowest and loudest sample).

[Milhouse]

Yes. Normalize brings the complete signal back into the range, where as normalize disabled keeps the "loudest" samples. The DRC compression this normal boost applies (dvdplayer settings) uses the loudest samples in the algorithm therefore you hear that difference.

So it seems to me, at least with a 2.1 setup, that center boost is ineffective while "normalise levels" is enabled.

If this is expected behaviour, and from fritsch's description - many thanks - it sounds like its working normally, perhaps the center boost setting field should be disabled while normalise levels is enabled? This would make it clear that center boost has no effect while normalise is enabled.

@DBMandrake: Thanks for the explanation, I think I understand.

[fritsch]

That center boost is something additional. FFmpeg does boost "a bit" by default, this "special boost effect" applied with the above patch and normalizing afterwards does removed this effect completely only in academic samples. It's a use case to have "extra boost" on center channel but also normalize afterwards :-)


academic samples:

before: 1.0 1.0 1.0 1.0
after (special boost): 1.2 1.2 1.2
normalize: 1.0 1.0 1.0

We are also talking about "downmix" - therefore the center channel must be boosted _prior_ to mixing - as you see in the code. It's made louder so that a bigger part survives mixing. Not that easy I know.

[popcornmix]

So it seems to me, at least with a 2.1 setup, that center boost is ineffective while "normalise levels" is enabled.

Try playing a "channel test" sample (e.g. one that cycles through front left, front right, centre, rear left, rear right, ...) and set the boost to 30dB with normalise enabled.
You should find centre is a little louder than previously, and the other channels are almost inaudible.

You can see this in the matrix coefficients reported:

By default it looks like:

Code:

13:25:52 181.066055 T:3051701344    INFO: CActiveAEResamplePi::Init    0.41   0.00   0.29   0.00   0.29   0.00   0.00   0.00
13:25:52 181.066437 T:3051701344    INFO: CActiveAEResamplePi::Init    0.00   0.41   0.29   0.00   0.00   0.29   0.00   0.00

With 30dB centre boost:

Code:

13:26:31 219.596161 T:3051701344    INFO: CActiveAEResamplePi::Init    0.04   0.00   0.93   0.00   0.03   0.00   0.00   0.00
13:26:31 219.596466 T:3051701344    INFO: CActiveAEResamplePi::Init    0.00   0.04   0.93   0.00   0.00   0.03   0.00   0.00

Note the third column is centre. It is about 3 times larger (on a linear scale), and the other channels are about one tenth the value.

30dB is way too high for real use, but is useful for testing the effect is visible.

[popcornmix]

Also, will this benefit users with a 5.1 etc AVR set-up or is it primarily to boost the centre on a 2/2.1 channel TV type of set-up?

It's designed when downmixing to stereo. If you have a 5.1 receiver it probably has options to boost individual channels, and probably has a night mode which may have a similar effect.

However it will apply whenever any mixing is done. I'll need to check the exact logic, but I think there is a shortcut when the mixing is known to be a no-op (i.e. source channels == dest channels in number and layout). We may want to disable that shortcut when "centre boost" is non-zero.

[evangelion]

Thanks for the reply, I already have the centre channel boosted using the AVR's GUI, but would prefer to have that set to it's default across all speakers, (with minor adjustment for distances etc) The Sony AVR's GUI is a nightmare to navigate to, hence my inquiring mind wondering if this patch would be usable on an individual basis.

[Milhouse]

Thanks for all the explanations, though it makes my head spin.

I've run a channel test and can hear exactly what you describe popcornmix.

I think I'm going to settle on +15db Volume amp, 9-10db center boost (maybe tweak down if there's clipping), and normalise levels disabled.

[da-anda]

Perhaps we should add some text in the Normalize description: "If you plan to use DRC compression, keep this setting disabled as it minimizes the effect this compression wants to achieve." In fact this drc compression works best when the variance is quite big (between lowest and loudest sample).

Is DRC supposed to mean "dynamic range compression"? If so, please no abbreviations in descriptions in case this will be added to master.