More realistic lowpass filtering

[adelespinasse]

Currently it's a BiquadFilterNode in lowpass mode (12dB/octave rolloff) with minimal resonance, sweeping down from a high frequency to a lower one (or sweeping up, or staying constant, depending on parameters). It sounds ok, but could probably be better. What are the actual rolloff characteristics in real spaces? My intuition is that a gradually spreading Gaussian "blur" FIR would be about right, but that's just a guess.