Free spectral analysis tools for mixing and mastering

[HarperYR]

Visual feedback can be really helpful when mixing and mastering. What free spectral analysis tools do you use? I'm looking for spectrum analyzers, spectrograms, correlation meters, etc. Some of these free audio utility plugins can reveal issues you might not hear. What are your favorite free tools for visualizing your audio, and how do you use them in your workflow?

[JackYJ]

For free spectral analysis tools, Voxengo SPAN is the gold standard. It's free and more powerful than many paid options. For spectrograms, Sonic Visualiser is free but separate from your DAW. These free spectral analysis tools are essential for identifying resonances and checking stereo image. I use SPAN on every mix bus.