Late Reverberation

Desired Qualities:

1. a smooth (but not too smooth) decay, and
2. a smooth (but not too regular) frequency response.

• Exponential decay no problem
• Hard part is making it smooth
  
  • Must not have ``flutter,'' ``beating,'' or unnatural irregularities
  • Smooth decay generally results when the echo density is sufficiently high
  • Some short-term energy fluctuation is required for naturalness
• A smooth frequency response has no large ``gaps'' or ``hills''
  • Generally provided when the mode density is sufficiently large
  • Modes should be spread out uniformly
  • Modes may not be too regularly spaced, since audible periodicity in the time-domain can result
• Moorer's ideal late reverb: exponentially decaying white noise
  • Good smoothness in both time and frequency domains
  • High frequencies need to decay faster than low frequencies
• Schroeder's rule of thumb for echo density in the late reverb is 1000 echoes per second or more
• For impulsive sounds, 10,000 echoes per second or more may be necessary for a smooth response