SPAN

Does exactly what you need it to (analyse frequencies accurately and in real time). I like using it to see what saturation and exciter plugins are doing to the signal.

This is the best free analyzer out there. I use this when I need really precise measurements because the settings are very extensive.

Again, Voxengo offers a free product that not only performs like similar paid products, but surpasses them. Get this plugin, learn how to use it correctly, and listen to your mixes get better almost instantly.

SPAN is awesome. It has all that you can desire from a spectrum analyzer. All the info, all the analysis, everything you need to have all the data of your song. Put it at last of your master channel and see in real time how your mix/master is going. and it's free.

I use version 3.1 with Logic Pro X 10.4.2 on High Sierra. Never had a problem/crash.

Introduction
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Best free frequency spectrum, volume and phase correlation analyzer out there! It should be an 11 out of 10!!! AND free!!!!.

Features
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-) Real-time FFT spectrum analyzer
-) Volume meter
-) Phase correlation meter
-) Edit: Fourier block size, FFT window overlap percentage, visual slope, smoothness, and many more
-) Colors can be changed
-) Route different channels in one analyzer and compare them
-) K-Level metering
-) SCalable GUI
-) Statistics
-) Band-pass filter to listen to the frequency you're pointing at
-) Zoom in
-) Shows note as semitone and cent (not many analyzer do that)
-) more more more...
-) Freakin' free!!.

GUI & Usability
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GUI is ok and includes different color schemes. The behavior of the analyzers can be adjusted to the situation and taste. And you can scale its x and y axis as you wish, make it double huge or just small, or everything in between. Almost no paid (and some for a lot of money) analyzer can do that. But Voxengo nailed it for free!!.

It's easy to use and self-explanatory. If it should be too difficult for you, delete the .component, no money lost because it's free!!.

Presets
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It already includes very useful presets, for all different kind of situations. Albeit it's free!!.

Stability
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It runs, and runs, and runs... for free!!.

Cons
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I'd love to have the volume meter alone, but hey no complains here it's free!!.

Conclusion
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If you don't have Voxengo SPAN, you definitely must get it right now. Because it's darn good and costs nothing, yes it's free!!.