Topic: Mixing SBD+MIC levels in Vegas

[stantheman1976]

I can esily match up a SBD+MIC combo in Vegas but I'm having trouble with clipping once the two are mixed together.

I have a particular recording from this weekend where the recording from the mixer peaked at about -3dB and has plenty of dynamic range under that.  Then I had a D50 recording in 24/96 also that I normalized to peak at -3dB also. 

If I match the two in Vegas they sound decent mixed as just two stereo sources and only have a could spikes that go over.  I can drop the SBD source down a few dB and it works fine. 

I tried experimenting with the stereo image by duplicating the mic track, and either panning one to the left and one to the right or right clicking and choose Channels>Left or Right only.  Now the same recording that was not clipping is getting up to +3-4dB in some spots even though I haven't changed the levels.

So what can I do to get multiple sources to mix together properly without clipping?

[easy jim]

What you are noticing is summing, which results from the combination of the two stereo sources down to one.  When the tracks are well lined up, there will be more summing and less cancellation in the resultant mix.  Due to summing, the resultant mix will typically be somewhat more dynamic than either individual stereo source. 

Some choices to address summing that results in clipping include: proportionately lowering the levels of both source tracks a little so that the summed mix does not clip, using dynamic processing (compression/limiting) on either the stereo bus/master track or the source tracks, equalizing to reduce peaks at any frequencies that are excessive, etc.

[stantheman1976]

I get what you're saying.  Is there a VST plug in that limits the output before it's processed?  In other words, can I master both at -3dB peak and mix to taste without worrying about summing issues and then have the final mix limited by a plug in?

[beatkilla]

The audio levels add up....20db + 20db = 40db.

Just adjust the sliders on each audio track until there is no clipping.Or use track compressor to clamp down on the signal.

[ghellquist]

The audio levels add up....20db + 20db = 40db.

Sorry, the math works a little differently.

Assuming you add two signals reading the same level:

If the two signals are exactly the same, adding them will increase the volume by 6dB.
Uncorrelated signals will increase the volume 3dB.
In real-world music this often ends up at about midway, ie 4.5 dB.

Gunnar

[ghellquist]

I get what you're saying.  Is there a VST plug in that limits the output before it's processed?  In other words, can I master both at -3dB peak and mix to taste without worrying about summing issues and then have the final mix limited by a plug in?

One example of a plug is called a limiter. This is what mastering engineers use as one of the last steps. A limiter works by pulling down the very few strong peaks that goes up above 0dB FS (you can generally set the limit).

Of course what your on the radio and CD-s today is often overly compressed material. This is (too) easily created by increasing the signal going into the limiter. When feed a weak signal the limiter will not do any difference. If the signal is increased it will start to engage on only the very largest peaks but the ear will not notice it. The effect is simply an increased volume which the ear likes. Increase the input signal even more and the ear will notice more and more distortion. Well, it might be that people like the distortion.

Gunnar

[stantheman1976]

I understand.  I just don't have any experience with a limiter at the end of the chain.  The few times I've mixed two music sources I just adjusted each source and sometimes use a volume envelope to take down peaks, but the latter is time consuming.  I don't want to overdo anything but it would be nice to mix two sources that are peaking at about -3dB and have something to bring down those few spots where ti goes over.  That's where I was hoping someone knew a decent VST limiter plugin.

[tgakidis]

In Vegas there is a out master volume control used to adjust the output volume of the mixed source.  Click View, then click mixer.  You can adjust right & left independently by clicking the padlock icon.  PM me if you need a walk through and i will give you my phone number.

[Dr.FOB]

When adding channels in Vegas I find it best to attenuate each channel 3db.
That is unless you desire a ratio different than 50/50.  Do this with the volume slider in each channel.
If you are adding a third, you must drop 6db.

This will maintain the same dynamic range as the original program material.  If you don't lower your levels and just run a limiter, you will end up reducing the range between your loudest and softest passages.

[easy jim]

When adding channels in Vegas I find it best to attenuate each channel 3db.
That is unless you desire a ratio different than 50/50.  Do this with the volume slider in each channel.
If you are adding a third, you must drop 6db.

This will maintain the same dynamic range as the original program material.  If you don't lower your levels and just run a limiter, you will end up reducing the range between your loudest and softest passages.

The italicized is not really accurate in my experience.  When mixing multiple, properly synced, stereo sources down to one stereo track, some transient peaks will tend to be amplified to an extent that exaggerates the dynamic range of the summed mix as compared to the source tracks. 

You can see this effect when mixing 2 stereo sources (AUD and SBD) if you slightly adjust how they are synced/lined-up along the time ruler.   As you get them as close as possible to a 'perfect' sync on the time ruler, you will notice that the maximum peaks are noticeably greater vs. when the tracks are slightly off from each other.  It is a great way to see a visual demonstration of summing (as well as potential phase cancellation if they are 'off' just right).

[boojum]

Yes, summing is a problem when combining tracks.  I also find that I do not want adding equal amounts of SBD and MIC.  You may have to play around with this when you are mixing to get the right blend.  Also, there may be alight phase differences between the SBD and MIC tracks which you can correct.

Cheers

[stantheman1976]

How can I know if there are phase issues and correct them?

[easy jim]

^ There are a couple common ways to see if two sources are out-of-phase once they are lined up. 

First, zoom in as far as possible on a loud peak and see if one source has 'peak' or positive amplitude while the other source has a 'valley' or negative amplitude.  If so, they are likely somewhat out of phase and will - at least partially - cancel each other out. 

Second, use a real time analyzer to watch the frequency response during playback of the resultant mix of the two sources and look for comb filtering.  If there are obvious frequencies where there seems to be a lack of amplitude, especially if you have the same thing happening in harmonics of those frequencies (for example, at 60Hz then 120Hz then 180Hz, and so on), you are probably seeing comb filtering caused by cancellation from the sources being out-of-phase with each other. 

You can now try inverting the phase 180 degrees on one of the two sources, and then see if that alleviates the apparent comb filtering.  If a phase inversion does not work, or only partially seems to work, you can also try shifting one source a little (fractions of a milisec) along the timeline in an effort to minimize the phase cancellation.  Most of the time, with a SBD and an AUD source, it is inevitable that you will have some phase cancellation - an effect of how the room reflections change the waveforms as they are captured by your mics vs. the 'raw' waveforms as they are passing through the SBD console directly to your recorder.