Rectangular (no) window for FFT spectrum analysis.
Window function: W[n] = 1.0 (no tapering), where n is the sample index and N is the window length.
Pass this value to the window parameter of AudioListener.GetSpectrumData or AudioSource.GetSpectrumData. Unity still applies this unity window before the FFT.
The rectangular window preserves the full sample block and gives the narrowest effective main lobe, but it has the most spectral leakage. Use it for quick visualization or when neighboring bins bleeding into each other is acceptable. For analysis where peaks must be distinct, prefer FFTWindow.Hamming, FFTWindow.Hanning, or a Blackman-family window.
Additional resources: FFTWindow, FFTWindow.Hamming.