Projects / Non-Exponentially Decaying Late-field Reverberation

A Reverberator with Two-Stage Decay and Onset Time Controls

Background: Room acoustics in the complex spaces

Example #1. Balcony in the opera hall

(photo from oscar wilde)

• Reverberation time in the balcony is short (=fast decay), but the rest of the opera hall has long reverberation (=slow decay). So, what tends to happen is that you hear multi-stage decay.
  

Example #2. Separated rooms by the almostly closed door

(photo from arealhousewifeofnyc)

• When a noise is made inside the door, you might hear a little bit of energy first, and then a little more. In this way, it might take a while for the energy's build-up, and if there is something like a hallway between the rooms, it takes longer. So, you might get a delayed onset in the reverberation response.
  

Efficient Reverberator Structure for Non-Exponentially Decaying Reverberation

  

• Combined Comb Filter Structure
• Controls the envelope of non-exponentially decaying reverberation
• Switched Convolution with Short Noise Sequences
• Increases echo density
  

Comb Filter Structures

Two-Stage Decay Using Parallel Comb Filters

- Comb Filter Structure: - Comb Filter Equation:

Delayed Onset Using Series Comb Filters

- Comb Filter Structure: - Comb Filter Equation:

Switched Convolution Reverberator with the Second-Order Comb Filter

• Parallel & Series Comb Filters can be generalized into a second-order comb filter structure.
  
• Overlapped switched convolutions with short noise sequences increase echo density for natural sound.
  

Result

Sound Samples 1. Two-stage Decay Impulse Response  Drum Sample        2. Delayed Onset Impulse Response  Drum Sample         * Original Drum Sample Demo VST Plug-in SCRevNoExp.vst

[Note] 1. For all sound samples, the reverberation time of the comb filter C2(z) is fixed to 2 second. 2. For the case of two-stage decay, that of C1(z) is 0.5 second, and for the case of delayed onset, it is 1.5 second.