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How to Use Voxengo's SPAN: Part 2

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Read Time: 4 min

Last time we took a deep look into the FFT window of Voxengo's SPAN. With adjustable timings, resolution, and the ability to layer multiple sources on top of each other, SPAN's FFT capabilities are awesome. If that were not enough for a free plugin, SPAN also includes amplitude and phase metering as well!

Amplitude Metering

Many engineers forget that there is more than one way to measure loudness. Different situations call for different standards of measurement. Thankfully, Voxengo's SPAN includes a plethora of options for the loudness-conscious engineer.

The Basics

Upon loading SPAN, you should have your FFT (fast Fourier transform) window in the center along with the amplitude meter on the right. The meters will default to a peak style setting with the special white line indicating acting as a peak hold so you have time to read the peaks.

At the bottom of the window you will also see the Statistics window. While nothing fancy, it gives you a solid number read out of your peak RMS and overall peak levels. Knowing how loud you got is always good information to have!

Also note the portion in statistics dedicated to Max Crest Factor. For those unaware, this handy little readout is the difference between your RMS and your Max RMS. This measurement is very good for seeing just how dynamic your track really is.

If you do not see the amplitude metering, double check you do not have Hide Meters and Stats clicked! This makes SPAN a strict FFT-only program, but you knew that from the previous tutorial right?

Getting a Little Deeper

The cool amplitude metering aspects in SPAN are buried away in menus. (Curse you, clean interfaces!) Let's start with Settings directly above the amplitude meter.


The unfortunate aspect of this menu is that it includes a lot of controls for how SPAN looks. However if you ignore the clutter, the bottom right corner has options for our amplitude meter.

  • Integration Time - This control changes how long of a window the amplitude meter will use for calculating average loudness. The higher the number, the closer you get to an accurate RMS measurement. However, transient loudness will of course be smeared.
  • Release Time - The release time controls how long it will take the meter to fall at least 40dB. By shortening this control you can gain better transient resolution even with a high integration time. However depending on how your controls are set it could become very hard to read.
  • Peak Hold Time - Finally this feature adjusts how long the white lines in the amplitude meter should stay in position. While they can always go up, sometimes getting a good peak reading is tricky. This should help get the timing just right!

Measurement Standards

Back under the Statistics portion of SPAN we have the nifty ability to change our measurement standards for loudness. By default SPAN will use dBFS (dB Full Scale), since it is a format most engineers see everyday. However there are some other useful features as well.

  • dBFSThis standard form of measurement most DAWs use to this day. RMS measurements in dbFS can be a little hairy depending on the implementation. However peak readings are always spot on.
  • K SystemDeveloped by Bob Katz, this modern metering system involves not only the meters, but your monitor gain as well. By switching between the various K-12, K-14, and K-20 options you dial your metering and gain in for different audio material. K-20 is meant for wide dynamic range content, K-14 for medium range, and K-12 for small. The versions with a "C" attached are for calibrating your monitors to the K System.

Phase/Correlation Metering

The last useful measurement SPAN gives us is the Correlation Meter. In case you have never used this sort of meter before, this is how they work:

  • The plugin analyzes both the left and right channels of the audio stream to get an average amplitude. SPAN uses a three second window.
  • The correlation meter then compares the channels to see how in phase they are (digital audios range is from -1 to +1).
  • It tells you how in phase the content is via a meter from -1 to +1.

Now, before you go jumping to conclusions about the meter read out, be careful! Digital audio going from -1 to +1 does not have anything to do with the correlation meters -1 to +1.

If the correlation meter should register from 0 to 1 it is considered in-phase, and the closer to 1 it gets, the more in phase it is. However if the meter should fall between -1 and 0 then it will become more and more out of phase.

You will also notice a R/L read out in the same section. This tells you the difference in dB between the left and right channels. If the number is positive then the right channel is louder and vise versa for negative values. Easy and handy!


Voxengo's SPAN is by far one of the most popular freeware plugins for good reason, it just works! From overlaying FFT information to amplitude measurements and phase metering, SPAN is a fully featured audio analysis tool. 

Would it be nice to have ITU standards, a vectorscope, or some other analysis with it? Sure! But it is free so don't bite the hand that feeds you! Thanks for reading.

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