FFT analyzer
A modern spectrum analyzer with a focus on human audio perception. Recent release, very well thought-out. Pretty much a complete package. Can layer up to four graphs: same input with different settings (Mid, Side, smoothing etc.) or direct input and the sidechain input for referencing.
TDR Prism (free)
oscilloscope
A minimalistic oscilloscope that can sync the display with the BPM of the song (and provide a stable and readable plot). The sync features are the most important when it comes to oscilloscopes. Can do side-chain so you can layer two signals.
🟢 bomshankamachin.es/plugins/occularScope
Bom Shanka Machines occularScope (free)
FFT analyzer with low-end optimization
It has Mid-Side capabilities, so it can be used to measure stereo field correlation. It can provide the overview of the tonal balance with a smooth line and then it displays the spectrum with 128 dynamic bands. It makes it easy to spot the kick’s low end sweep and bass fundamental and top harmonics. Also it has side-chain, so you can feed a reference audio (the faint green line - in my case is a Brown Noise generator).
🟢 reflex-acoustics.com/products/reflex-spectrum-analyzer
Reflex Spectrum Analyzer (free)
FFT spectrum analyzer with broadband correlation meter