Audio Meters - Mono vs Stereo 6db difference?

Greetings

I hope that the wisdom of the forums can explain something that has eluded me for nearly 5 years of Final Cut Pro X use and internet searches.

When I use a limiter to raise the audio of a mono track to 0 dB (for test purposes), the audio meters show the signal topping out at -6 dB. If I do the same thing with a stereo signal, the two meters agree. Why is this?

Here is link to a screen capture showing the 6 dB difference on a mono signal.
vimeo.com/treeswingvideo/review/476131581/4dbc7254be

Thanks.

Geoff

A limiter is not meant to "raise" levels but to "limit" the existing levels. Gain raises levels, limiters and compressor lower/limit levels. Plus, how are you adjusting these effects, or are you just applying them with no tweaks?

Thank you for your reply. I didn't give enough information. Let me try again.

I am using the limiter effect to raise the gain of the track but limit it to 0 dBm for the purposes of demonstration. Normally I limit to -3 dB. I have attached a screen shot of the limiter with its settings and the audio meters.



I have added +9 dB gain which causes the limiter to kick in and reduce the peak by 5.9 dB. The output meter of the limiter tool shows that output is limited to 0 dB.

The master audio meters of Final Cut, however, show the output peaking at -6 dB for this Mono signal.

When I apply gain and limit a stereo signal, however, the output meter of the limiter tool and the master audio meters agree.

The video link show this response dynamically.

Thank you for your help.

Geoff

This is how FCPX works with audio. When you add two mono files in a Stereo timeline, you double the loudness +6db. FCPX compensates this and applies a downmix attenuation -6db. This is something logical.
If you add only one mono file in your stereo timeline, you need to up the gain 6db (for cancel the downmix attenuation) or you can add twice the same mono file.
Sorry for my bad english.

Thank you. That is what I had figured out empirically, but I just needed to confirm that others see this as well and that I am not crazy. Well, perhaps we haven't truly established my sanity, but at least this one observation is consistent.

Geoff