A rolloff factor to control the reverberation time for high relative to low frequencies. For example a ratio of 2 means that the reverberation time at Nyquist frequency will be twice as short as the reverberation time of DC, a 0 Hz oscillation frequency.
When the value of this ratio is less than 1, the high frequency reverberation time becomes longer than the lower frequencies. In some cases the HF Ratio used will be less than specified to avoid stability problems fundamental to the algorithm when using shorter reverb times combined with long delay times and higher HF ratio.
Default value: 2
Range: 0.5 to 10