Make VU Meter norm conform

We may look at this GPL2 code:
https://github.com/x42/meters.lv2

Software VU Meter Ideas:
http://music.columbia.edu/pipermail/music-dsp/2007-June/066267.html

Related:
http://www.mixxx.org/forums/viewtopic.php?f=7&t=7239

This will help to light up the correct LED on controllers with labeled VU-Meters.

Related:
http://www.mixxx.org/forums/posting.php?mode=reply&f=6&t=7872

Uff this is old. Trying to map the VuMeter to HID light output right now, but it's kinda hard without knowing the function to go from Mixxx's VuMeter to dB - is it somewhere?

Unfortunaely the VU meter is not scaled in DB:
https://github.com/mixxxdj/mixxx/blob/master/src/engine/enginevumeter.cpp#L73

That's one reason why this bug exists. Do you have interests to adopt it?

I have interest in adopting any bug that I comment on, but I first need an introduction to C++ and the codebase ^^

The best way is leaning by doing. This one is too advanced for the beginning. Take one "easy" tagged bug and follow https://www.mixxx.org/wiki/doku.php/bugfix_workflow

I've been thinking it would be helpful to have a psychoacoustic perceived loudness meter. Can we do this with libebur128?

Let's be careful how we adjust the VU meter. We need to make sure the clipping indicator is still accurate and intuitive. It could look strange if either the VU meter looked low and was clipping or looked very hot and was not clipping.

Right, we still need to know whether the deck is clipping regardless of the perceived loudness. It may be a good idea to not make EBUR128 the default but have it as an alternative option for users who understand how it works. I tried using the x42 EBUR128 LV2 meter plugin on some tracks in Ardour and it is clear to me that this provides more useful information than Mixxx's current metering. Tracks that look approximately the same with peak metering can appear very different with EBUR128 or K20/14/12.

> I've been thinking it would be helpful to have a psychoacoustic perceived loudness meter. Can we do this with libebur128?

Yes.

I think we face here different use cases.
It is explained a bit here.
https://www.waves.com/loudness-metering-explained

The current Mixxx VU meter is somewhere between a paek meter and a VU meter, offering a reasonable one fits all type, unfortunately not comparable to other devices or any standard scale. The clipping LED works always and independent of the VU-Meter scale.

If one likes to monitor the loudness of the mix, knowing that there is enough digital headroom anyway, a LUFS meter will be a better choice. This is relevant especially for MIC and Aux input, because we can trust the ReplayGain adjustment for tracks blindly.

If one likes to get all out of an underpowered PA System, True Peak meter be the best choice. It helps to predict digital clipping clipping after DA conversion.

Both meters would be a nice preferences option.

We also got this feature request over email:

"""
As a freelance broadcaster for many years I have pointed would be Dj's in the direction of the Mixx software download to get them started.
However I find that many ask the same question..."Does Mixx software contain a setting where we can use the old type studio desk VU meters for monitoring levels"?
I'm afraid I can't answer this one..can you advise and I'll pass any future enquiry information on
Regards
Brian Clough
Freelance Broadcaster/Journalist
"""

Regarding post #13 probably they can use the professional x42-meters through Jack, or the lv2 versions with a Jack enabled plugin host. The x42-meters can be found on distribution repositories also.

https://x42-plugins.com/x42/x42-meters

For precise results they may need levels allowed above 0dBFS at Mixxx's Jack output. -> See: Bug #1959153

I don't think Mixxx should need LV2 plugins for metering. However we could copy code from x42-meters into Mixxx.

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/7888