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Loudness meter discrepancy

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Loudness meter discrepancy

PostPosted: Sat Nov 24, 2018 1:03 pm
by SimonLyn
Hello all - just started editing some stereo files today and noticed something I can't explain, or work with :( ....

I have a single stereo file on a Reaper track, I place a loudness meter on this track and a second loudness meter instance on the master track. The program loudness and true peak metrics are exactly a 6dB quieter on the master track - why is this?

There's no funky routing, mono or M/S switching, or any additional processing at all ... I'm vaguely aware that the 6dB figure is associated with pan laws and digital summing, and have a feeling that I'm going to feel embarrassed when I figure this out :tongue:

...any ideas guys?



Re: Loudness meter discrepancy

PostPosted: Sat Nov 24, 2018 1:09 pm
by blinddrew
You haven't inadvertently lowered the send level in the routing options? Or got any post-metering plug-ins that might be lowering the gain in there? Including on meter plug-in itself?

Re: Loudness meter discrepancy

PostPosted: Sat Nov 24, 2018 1:13 pm
by Hugh Robjohns

My initial thought, like you, was that it's a pan-law thing... But you're working with a stereo file on a stereo channel, so I wouldn't expect the balance control to be having any effect.

I don't have an answer, I'm afraid, but you should be able to track it down with some experiments using reference sine tone files of known amplitude, and standard digital peak meters in various locations throughout the signal path to find out where your 6dB level shift is being introduced.


Re: Loudness meter discrepancy

PostPosted: Sat Nov 24, 2018 2:17 pm
by Wonks
The track meter will be an insert, so the output will be affected by the track fader. If that's not at 0dB, then you'll get different values. I'd also check that your target loudness values on the two meter instances are the same.

What about the peak metering on the channel and the master? Are they showing the same peak values or is the master also showing peaks 6dB down on the track meter? If so, can you switch the track meter to post-panner , rather than pre-panner (I don't know Reaper but I assume this should be possible)? If that then drops the channel peak meter down by 6dB, then it is definitely something to do with the way the panner works.

I assume that it is a true stereo track, and not a stereo file placed on a mono track? (I think Cubase allows you to do this if you force it to). I could then see how the panner could affect the output level, whilst a stereo track on a stereo channel would have a balance control, which shouldn't have any effect on levels when set centrally.

Re: Loudness meter discrepancy

PostPosted: Sat Nov 24, 2018 2:54 pm
by SimonLyn
Thanks all for your help! I have managed to sort it out - Reaper has a per-project pan law setting which I had at -3 dB. Resetting this to the default 0 dB brought my two loudness meters back into alignment.

There is also a 'gain compensation' option for the pan law settings which as I understand it leaves the centred level alone whilst increasing the level at the L/R extremities to compensate. This also gives an identical reading on my loudness meters.

The 6 dB discrepancy only happened when my stereo file was grouped in a folder track, so not sure about that one ... Love Reaper, but sometimes it gets in my way :roll:


Re: Loudness meter discrepancy

PostPosted: Sat Nov 24, 2018 3:42 pm
by Wonks
A stereo track shouldn't be affected by the balance control. This should be a different animal to the pan pot on a mono track. On a stereo track, say you wanted to balance the track to the left. As you bring the control to the left, the left track volume stays the same but the right hand track's volume is reduced. The more to the left the balance control is positioned, the more the right track's volume is reduced.

On a mono track, the pan pot can operate in one of two ways, depending on the DAW used (and sometimes the options available on that DAW). Either:

1) The full left and full right pan positions are boosted by the value of the pan law used (3, dB, 6dB, equal power etc.) with the centre position being no boost.

2) The centre position is cut by the value of the pan law, and the full left or right pan positions are at the track's normal level.

This is why I normally prefer to have the metering post-panner, though if you do this it helps to know what type of pan law you have set and which way it operates in the centre position (boost or cut), as you can then use that knowledge to help set the levels when gain-staging your channels e.g. if you are trying to set a nominal working level of -12dB on a channel, then for mono channels with the pan centred, then with a 6dB pan law, with a DAW that boosts the centre position by 6dB, then (with post-panner peak metering) you'd need to aim for an indicated -6dB, whereas with a DAW that cuts the full L and R positions by 6dB, you'd just use the nominal -12dB level. Pre-panner metering is easier, but if you are interested in knowing what the actual level passed on to group and master tracks is, then post-panner is (to me) more informative.