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  2. Audio Production

How to Use the VST Plugin Analyzer

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As audio engineers, we often have to walk the line between the artistic and the scientific, the subjective and the objective. However sometimes keeping our eyes and ears on the objective can be difficult. That is where tools like the VST Plugin Analyzer come in.

The VST What?

A Lowpass Through the VST AnalyzerA Lowpass Through the VST AnalyzerA Lowpass Through the VST Analyzer
A Lowpass Through the VST Analyzer

While our ears should always be the deciding factor for us as audio engineers, sometimes having visual cues can be a great asset. From FFT analyzers, to phase meters, to spectral  mapping, there have always been good tools available for analyzing our mixes.

However, when it comes to analyzing the plugins we so readily rely upon, we generally do not have  access to dedicated tools. Sure, we can feed sine waves or noise into the various analyzers we have, but they do not always give us the full picture.

The VST Plugin Analyzer by Christian Budde seeks to give us an extremely objective and analytical view of our plugins. Whether it is the frequency response, total harmonic distortion, transfer function, or whatever else, this handy standalone software can tell us more about our plugins than our ears can. Plus, it is free!

However, like much of the freeware available, not everything is as polished from the user's standpoint. But with a little guidance, you'll be able to see your plugins in a whole new light!

How It Works

Distortion is Not Always a Bad ThingDistortion is Not Always a Bad ThingDistortion is Not Always a Bad Thing
Distortion is not always a bad thing.

At the core of it all, the VST Plugin Analyzer is a series of standard scientific measurement tools and a VST host, coded into one neat little package. While the basic operation is simple, there are plenty of hidden controls lying underneath the surface.

Getting Started

Here is a general guideline to get you started:

  • Open the software and you will be greeted by a standard unassuming window with only three drop down menus.
  • Go to VST Plugin > Load and choose your desired plugin. Keep in mind that only 32-bit plugins work! The software was not meant for 64-bit plugins, and will crash if you try to load one. The 32-bit versions will work the same from a measurement standpoint, so do not worry about "losing quality" in your measurements.
  • You should then be see the plugin loaded just like you would inside your favorite DAW.

Basics of the Measurement Window

After you've loaded the plugin you can begin to run various measurements. The easiest one to get started with is frequency response, since we're all familiar with seeing these on microphones and speakers.

In order to run this measurement, simply go to VST Plugin > Measurement > Frequency Response. You should now see a new window pop open with frequency on the x-axis and dB on the y-axis.

Depending on the type of plugin you choose you should see either one purple line, or two red and blue lines somewhere in the frequency window. These lines are the measured audio signal of the plugin in the VST Plugin analyzer. Having red and blue lines indicates that the plugin effects the left and right audio channels differently, where as a purple line shows that both channels are effected the same (red + blue = purple).

If you do not see any purple, red, or blue lines, then you may need to adjust your view to find the audio signal.

  • To move up and down in a measurement window hover your cursor over the y-axis and left-click + drag or scroll your mouse wheel. With frequency response (particularly in "always on" compressors), your signal line may fall below the zero point.
  • To change the scale on the x-axis, right-click and drag left or right in the measurement window, and it will auto adjust the extreme ends of the x-axis (in this case, frequency).
  • Sometimes we may need to zoom in on one particular area. To do so simply left-lick and drag to the right in the measurement window to highlight the region you wish to zoom in on.
  • If your scale/zoom ever gets messed up, or your signal is so extreme that you cannot view the entire plot in the window, left-click and drag to the left to reset your graph. Keep in mind that doing so may adjust the scale of your axis to something different to when you loaded the window.

Viewing Different Measurements

Soft Knee Compression Transfer FunctionSoft Knee Compression Transfer FunctionSoft Knee Compression Transfer Function
Soft Knee Compression Transfer Function.

Available Measurements

While the above gives us information regarding frequency and amplitude, there are a host of other options as well. Some are obvious and others not so much. Here are where to find the other forms of common and useful measurements:

  • Phase Vs. Frequency - While in the Frequency Measurement window, go to Domain > Phase (wrapped). This feature will show you how the phase shifts (in degrees) relative to various frequencies. Analog-style filters should show all kinds of phase shifts where a linear phase should be a straight line.
  • Group Delay - Go to Domain > Group Delay in the Frequency measurement window in order to view this graph. This is related to phase and tells you how quickly or slowly some frequencies arrive.
  • Impulse Response - This measurement can be found by going to Domain > Time. You will most likely need to right-click + drag to the right to see the result, however it can be useful for analyzing how a filter behaves.
  • Harmonic Distortion - To determine the THD (total harmonic distortion) of a plugin at a given setting, go to VST Plugin > Measurement > Harmonic Distortion. This measurement generate a 1kHz tone and measures the resulting distortion from the plugin, as well as graphing it. The results can be see in the top right of the measurement window. This is handy for seeing how clean or dirty a plugin is and if it produces even or odd harmonic distortion. (The VST Analyzer bottoms out at about -166 dB for THD. Realistically, anything -120 dB or less is just silly clean, since the best A/D converters stop at about -120 dB.)
  • Transfer Function - One of the biggest measurements for a compressor/expander/gate is its transfer function. This is accessible by going to VST Plugin > Measurement > Dynamics > Static Characteristic. This will tell you if the compressor has a soft-knee, hard-knee, or optical curve. The plot runs input on the x-axis and output on the y-axis. Keep in mind, the VST Analyzer has to constantly run this test, so there is a slight delay when adjusting the plugins parameters in this window.

Tweaking the Measurements

You will notice that many measurements in the drop down menus have shortcuts next to them. By activating these shortcuts, you gain access to modifying how the measurements are taken.

To access any of the additional tools, simply hit Shift-Ctrl-(letter). For example, if you press Shift-Ctrl-F, you will be able to change how the frequency measurements are taken.

Be careful here, as some shortcuts are not very friendly to the untrained eye!


Christian Budde's VST Analyzer is a amazingly useful tool for seeing just how your favorite plugins work. If you were ever in doubt about how a plugin behaved this, is a great way to check.

If your plots keep moving on you and do not remain static, chances are the plugin is constantly adapting to the input signal and has some form of analog modelling, so do not be alarmed! Or if you want to compare two plugins side by side, go to Plot > Store  in the measurement window, and it will save the current state of the plugin on the graph. Simply go ahead and load a new plugin and then compare.

So get out there and put your plugins to the test!

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