Voxengo's SPAN is an excellent free, 'fast Fourier transform' (FFT) spectrum analyser. We've recommended it in the past, in our Sound Tips articles, so we feel that it is worth devoting a whole article to it.
SPAN stands out as it has a fuller feature set than many of the paid spectrum analysers out there; it really is a fantastic tool. It provides you with a flexible, 'mode' system that allows you to configure the plug-in to work just as you like it. You can specify Fourier block size in samples, FFT window overlap percentage and the spectrum's visual slope. Even the colour can be altered to suit your mood!
In addition, you can choose to display a secondary spectrum of a desired type; for example, real-time maximum or all-time maximum. SPAN can monitor stereo, mid-side and surround channels, and one really nice feature is that the plug-in supports multi-channel analysis too. This means that it can be set to display spectrums from two different channels or channel groups at the same time. This is great for spotting issues at low frequencies that may not be audible on smaller speaker set-ups.
The plug-in is available for pretty much every platform; AAX, VST, VST3 and AU are all provided. Both Mac and PC are supported in 32 and 64 bit versions. You can download SPAN from the Voxengo website, and if you don't currently have a spectrum analysis tool in your toolkit, we recommend you go and pick up this plug-in immediately!
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