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AFDN-reverb

(High-Order) Ambisonics Feedback Delay Network Reverb

Nick Gang & Wisam Reid

Sound in Space, Spring 2017

Overview

The reverb architecture described here has the following qualities:

• Ambisonics encoded inputs and outputs
• Localization of direct signal and early reflections
• Real-time control of early reflection width
• Frequency dependent control of t60 times

What's Done

• Diagrams of the current architecture are available here
• Early reflection and late field FDNs implemented in gen~ code
• 3rd order rotation matrix implemented in max using gen~
• Faust library and demo files implementing algorithm from 1st-3rd order
• Faust code compiling live in Max using the faustgen~ object
• Max testing environments for running gen~ code and Faust code in real time

Future Work

• Tie delay-line lengths to physical descriptions of simple rooms
• Implement additional filter in wet signal path to simulate different wall materials
• ‘Ambisonics mangler effect’: This was our discarded initial thought for creating late-field, but it could lead to a cool effect. Each of the N ambisonics channels is added to a set of L delay lines through an NxL mixing matrix. These delay lines go through an FDN and are output as N channels to be decoded with an ambisonics decoder. Different LxL feedback mixing matrices may produce different styles of ‘spatial blurring’.
• Quantitative comparisons between algorithms using dummy head