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Author Topic: Rendering in wavelab montage is raising gain significantly  (Read 790 times)

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Online Gordon

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Rendering in wavelab montage is raising gain significantly
« on: March 19, 2017, 12:13:32 PM »
I ran into this issue a few years ago and can't for the life of me remember how to fix it and searching turned up nothing.  My work flow for 4 channels is:

I adjust gain in the aud or sbd as needed in wavelab (not montage) till they pretty much match but leaving them a few db's below 0.  Then when they are loaded into the montage by default the volume slider is the same for both (0 db).  If doing a 50/50 mix I generally drop each volume slider down to -1 db.

Here's my issue.  When I render said files the result is the gain is raised significantly!  For example last night I ran 4 channels mono.  The aud right and left peak at -2db.  when I render them together to make the stereo track the gain is raised about 5db!  So the peak is now +3db.

Same thing happens with stereo files.  I have an aud & sbd with no editing done.  The aud peak is -4.2db, sbd is -8.7db.  Render together and it's now -2.2db.  So the rendering process raised it -2.2 above the max of either one.  Again this is without raising the gain to match.  When I do that (aud -4.2db and sbd -4.2 db) the rendered file is -.02db.

The volume in master section is set to default and is not turned on (no green light).

I understand that mixing will raise the gain a tad but something is not right here.  I leave gain on both well below 0 so it should not be raising it this much!  I've dug all around settings etc and haven't figured it out.  Like I said I remember this happening before but don't remember what I did to solve it.  Until last week I hadn't done any 4 channel since installing wavelab on my new build so I hadn't noticed the issue.

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Online Gordon

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Re: Rendering in wavelab montage is raising gain significantly
« Reply #1 on: March 19, 2017, 12:42:02 PM »
 I'm playing around with the mono files again now. -2db peak on both channels. I set the volume slider in montage to -3db. rendered and it's still peaking over 0.
Mics: Neumann ak40 (din) > Nick mod lc3 > Naiant PFA, CA-11 Omni
Pres: Audioroot Femto, Naiant Littlebox v1 (2015 edition), CA 9200
Recorders: Sony PCM-M10, Tascam DR-70D

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Offline mjwin

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Re: Rendering in wavelab montage is raising gain significantly
« Reply #2 on: March 19, 2017, 03:35:52 PM »
Thinking about what you're doing here:  if you're trying to sum two signals whose simultaneous peaks are each greater than -6dB, this will result in clipping.  Don't forget that -6dB is the halfway point, so twice that will clip. The clipping will occur only at the point at which the audio is written to your final output file.wav as Wavelab's  internal processing is 32bit float (iirc). 

The simplest solution is to simply enable the master section, as you're doing, and attenuate the output by the required amount. But this will be as much as 6dB if you're summing 2 channels, more for a greater number of channels.   The alternative method is to ensure that your levels in the two files are lower to begin with, but that requires some hindsight as you probably don't know what your mix ratio will be before you compile the montage, and it doesn't offer any audible benefits anyway. 

Hope that helps.  I love the Wavelab montage feature btw. I'm trying to migrate to Linux  but I really miss that feature in Audacity!

Online Gordon

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Re: Rendering in wavelab montage is raising gain significantly
« Reply #3 on: March 19, 2017, 03:41:47 PM »
Yes it makes sense that combined would raise it but I'm seeing way more than I did in the past. I used to get both files to -1 or 2db then render with the slider on -1 or even -.5 and get a file that would roughly match what I had before render.
Mics: Neumann ak40 (din) > Nick mod lc3 > Naiant PFA, CA-11 Omni
Pres: Audioroot Femto, Naiant Littlebox v1 (2015 edition), CA 9200
Recorders: Sony PCM-M10, Tascam DR-70D

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Offline mjwin

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Re: Rendering in wavelab montage is raising gain significantly
« Reply #4 on: March 19, 2017, 04:31:10 PM »
I guess it depends on whether the sbd feed is time-aligned with your mics.  Sbd will be from stage mics, and your aud from however far back you are with 1ms/foot delay on the latter. So unless you're nudging these (in wavelab), your peaks won't necessarily coincide. 

You might be getting  a mix of additive/ destructive interference too as the waveforms mix, depending on the frequency of the loudest peaks.  When sources aren't synchronized it gets difficult to predict how things will mix, and  in any case it's going to be very venue/event/position dependent, even a few inches can make a huge difference.  What works ok for one show won't necessarily be ok for another, and some (most?) venues have huge resonant points which can make matters worse for certain frequencies.   

Have you zoomed into the waveforms to see exactly what's going on at the peaks?  Maybe go back and look at a recording where sbd+aud summed ok, and look at how the peaks coincide there. I don't think you've got anything bad happening here, but maybe you've just always got lucky in the past.  Hmmm... Anyone else got any ideas?

Online Gordon

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Re: Rendering in wavelab montage is raising gain significantly
« Reply #5 on: March 19, 2017, 05:02:21 PM »
thanks.  using a 4 channel deck (tascam 70d) so clock is the same.  In the past it's been an R44.

I always "nudge" the files to line up.

the show from yesterday was in a tiny brewery & was a literal stack tape.  mics about 1.5-2 feet from the speaker.  in that case I didn't need to nudge at all.

the show last week mics were hung in the sweet spot about 15-20 feet from stage.  a small nudge needed to line them up.

I found an edited 4 channel show from a couple years ago on the hard drive (using the r44).  The aud  = -1.2db.  sbd = -.39  I put both in montage, lined them up w/ slider at -2 = -1.2db.  w/ slider at -1 =  -.19.  so even with the gain that high I got  negative gain in the rendered file!
Mics: Neumann ak40 (din) > Nick mod lc3 > Naiant PFA, CA-11 Omni
Pres: Audioroot Femto, Naiant Littlebox v1 (2015 edition), CA 9200
Recorders: Sony PCM-M10, Tascam DR-70D

http://www.archive.org/bookmarks/gordonlw

Offline admkrk

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Re: Rendering in wavelab montage is raising gain significantly
« Reply #6 on: March 20, 2017, 03:02:47 AM »
I pretty much do everything in the montage. At the very least, I will let it play, with the volume on the PC turned down, and check the peaks before rendering. If all I am doing is adjusting overall gain, I will adjust the master, and do it all over again, to make sure there are no clips. Sure it takes a while, but I am not sitting in front of the computer other than to set, or check, the levels when it finishes.
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Offline goodcooker

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Re: Rendering in wavelab montage is raising gain significantly
« Reply #7 on: March 20, 2017, 08:31:56 AM »

I do all of my gain changes in Montage. No need to do gain changes separately. Never had a problem with gain being different after rendering. I use version 6.

You mentioned mono files. Are you panning the files to the different sides or leaving everything mono? On the left in Montage where you can send each file to it's panning location - RF right Front - LR Left Rear and so on...
Don't know if that would affect the outcome on render...just spit balling .
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Offline admkrk

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Re: Rendering in wavelab montage is raising gain significantly
« Reply #8 on: March 21, 2017, 01:16:44 AM »
That is an interesting though. I always set mono files to either right, or left, only. I can see where not doing that could make a difference, without previewing the output.
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Online Gutbucket

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Re: Rendering in wavelab montage is raising gain significantly
« Reply #9 on: March 21, 2017, 09:30:58 AM »
Summing two identical signals increases the amplitude of the output by 6dB.
Summing two totally uncorrelated signals increases the amplitude of the output by 3dB.

Most audio signals are "of the same content, yet somewhat different from each other" (which is why we are mixing them) and will sum to an amplitude value that measures somewhere in between those two extremes.

The more identical (correlated) the signals are to each other, the closer their summed amplitude will approach the +6dB end of that range.
« Last Edit: March 21, 2017, 09:33:14 AM by Gutbucket »
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