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How to Use Voxengo's SPAN: Part 1

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Read Time: 5 min

While simple on the surface, Voxengo's SPAN is a fully-featured metering plugin that can tell you loads about your mix. From comparing frequency responses to multiple measures of loudness, using SPAN will make fixing problems a cinch.


For those of you unfamiliar with Voxengo's SPAN, this little plugin is one of the most downloaded and used plugins available today. Why? Because it works well and it is free! Did I stutter? Free!

However, as with many fully featured plugins SPAN does not always get used to it's full potential. Why? Because a lot of the cool features are either buried in menus or require extra setup in your DAW. But no longer shall these goodies go unused! Because we are going to show you just how SPAN works.

Frequency Response

The most basic and prominent feature of SPAN is the Spectrum window. Simply slapping the plugin on any channel with audio will cause the Spectrum window to render a nice FFT of the incoming audio. Here are some additional basic controls for this window:

  • For a larger window, press Hide Meter and Stats at the top of the window. This will hide the other various meters.
  • If you are looking to find one very problem frequency but it disappears too quick, press the Hold function in the top left to have SPAN stop, and hold the FFT at that moment.
  • For additional control over the FFT, go to the Mode menu on the top right. Here you can choose everything from a default option, to 96kHz monitoring, to a high resolution.
  • To zoom in on particular frequencies or zoom in a dB range, use the two X and Y axis sliders.

Tweaking to Your Heart's Content

If you desire even more control than the preset modes, click on the Edit button next to the modes. The new resulting window will allow you to customize the FFT to your liking. 

Here are some of the notable controls:

  • Type - This allows to change how the FFT measures the incoming audio. Generally you will want to leave it on real-time average, but there are options for maximum amplitude, real-time maximum, and a (constant) average.
  • Block Size - Adjusting this parameter tweaks the frequency resolution of the FFT. A higher number results in a more accurate frequency response with less averaging between the bands. However, the higher the block size, the slower the FFT is to react.
  • Overlap and Average Time - These blocks control how responsive the FFT is while at the same time controlling how long the real-time average should last. If you find yourself wondering why what you are hearing is not quiet matching what you are seeing, the music might not be well lined up with the average time.
  • 2nd Spectrum - For those of you who like loads of information, here is your ticket! By activating the 2nd spectrum, you can now have two different analysis of your audio at the same time. The 2nd spectrum will be a darker and slightly more translucent in color.
  • Freq Low - This option allows you to control just how far down the FFT will monitor. Note that this different from the zoom sliders in the normal Spectrum window.
  • Freq High - Just the opposite of the Freq Low, this control will extend your frequency response monitoring even higher (assuming you are working in a high sampling-rate project).
  • Range Low - Adjusting this parameter will tweak the bottom threshold of the FFT's amplitude.
  • Range High - Adjusting this knob will control the upper amplitude limits of SPAN's FFT display.
  • Slope - This option will change the dB/Oct of the FFT display. Generally speaking do not touch it unless you are trying to mimic a very particular measurement standard.

Multiple Frequency Response

One of the coolest features of SPAN is the ability to have the FFT of multiple sources displayed at once. 

Why do such a thing? Because:

  • You can see where the sources are fighting at different frequencies
  • See how your mix/master matches against a similar commercial recording

So with that in mind...

Setting up Multiple Sources in SPAN

If you have never setup multiple sources into one plugin, setting up SPAN can be a little daunting at first. However, after a run through or two you it should become second nature!

  • First add SPAN either to the source you want first or place it on an empty track
  • If you placed SPAN on a empty track, use an AUX SEND to send your first source to inputs 1-2 on the SPAN track.
  • Next add another AUX SEND from your second source to inputs 3-4 on your SPAN track. You should now have 4 channels of audio on one track.
  • Inside SPAN, go to the Routing menu at the top.
  • Once the Routing window pops-up, you should see a section called Input Routing.
  • Inputs L-R (1 and 2) should read A-B, and In-3 and In-4 should be blank.
  • Change In 3-4 so they are using inputs C-D.
  • Back in the primary SPAN window, go to the Underlay drop down menu.
  • Choose Underlay 2.
  • You should now have both sources in one window!

While it might seem complicated at first, it really is not too bad. Some of you might be wondering why we see four channels of audio but only hear our primary channels, despite routing more channels to SPAN. The trick lies in the Routing window.

At the bottom of the routing window there is a section called output routing. If you setup multiple inputs you will also notice multiple outputs. However, just as with the In 3-4, the Out 3-4 has no source yet. If you were to assign Out 3-4 to C-D you would hear all four tracks.

Why doesn't Voxengo make this default? Because most people do not want to try contending with four channels of audio on one track. Furthermore most plugins cannot handle that much. So to keep things simple they simply default to muting any additional channels.

Conclusion For Now

From a frequency response standpoint, Voxengo's SPAN is immensely useful and tweak-able. While you should never mix with your eyes, having some visual cues can be very helpful indeed. 

Next time we will jump into the other monitoring aspects of SPAN such as phase correlation and loudness metering. Thanks for reading.

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