clipping at the device output

[James Lo]

I'm starting an audio cue before a previous audio cue ends.  When viewed individually on the Device & Levels tab, neither clip, but when they overlap, I can hear clipping which I assume is because they are summing at the cue output level and then clipping at the corresponding device output channel.  Is there any way to meter these summed levels within QLab 3.2.15?

[micpool]

Levels and Gain Staging in QLab has a few peculiarities. In no particular order:

The Level indicators on the cue output sliders in an audio cue are just that, indicators. They are not designed to correspond to any metering standard. Generally if the meter is going above the 0 mark on the slider and showing a bit of red, depending on the program material you may already be distorting or close to it.

On a heavily compressed pop track, a master slider setting of 0 and slider settings of 0 on the cue outputs will be driving the output of QLab quite close to clipping. When you play a second track it will probably clip

You can insert an AU meter plug in on a cue or device output in settings/audio/ edit patch. A free VU style meter is TB ProAudio MVM2, although if you were demonstrating headroom and gain staging in a class you would probably want to use a broadcast standard meter like Nugen Visualise, Izotope Insight, or Waves PAZ analyser.

Generally though, that's not necessary if you follow this rule for gain staging.

In your cue templates  set the default level for new audio cues MASTER to -10 (or -15 if you are going to be playing a lot of heavily compressed music tracks simultaneously). The Default level is 0 which is too high to allow headroom for even 2 loud audio tracks.

With a default master level of -10 instead of 0 you can play 5 uncorrelated loud tracks without any fear  of overload, and no need to meter. (uncorrelated just means the tracks are recorded at similar levels  but that the peaks are occurring in different places. If you had a close correlation between tracks, which might  be the case if you were beat mixing on a crossfade, so that the Kick on both tracks was occurring simultaneously you would still have sufficient headroom for 2-4  tracks  with the default masters at -10.

So in summary, always start with your master at -10 on any audio cue as the default and you will rarely  have to worry  about clipping anywhere in the QLab audio chain.

Mic

[James Lo]

Ah, that makes sense, thanks.  I also just realized why I've never run into this issue before: this is really the first time I've had to cue heavily compressed pop music.

[James Lo]

Is it bad practice to leave level meter AUs (mvm2) inserted with their GUIs closed in the cue file used for shows?  I tried to measure CPU usage with Activity Monitor and it seems like the number of cues running impacts CPU usage way more than having the meter AUs inserted.

[micpool]

In a word no, in 2, probably not!

Mic