AFC Yamaha Active Field Control (AFC) Immersive Audio System
What is AFC Enhance?
AFC Enhance controls the reverberation of a space while making use of the natural acoustic properties of the existing structure. Unlike approaches that add artificial reverb to the source sound to create a different impression, AFC Enhance employs technology developed over many years to control sound propagation within the actual space so that reverberation and volume can be altered while the natural sounds of musical instruments and voices are maintained. Relatively dead acoustic spaces such as event spaces, assembly halls, and banquet rooms that don’t have much reverberation are fine for speech, but if a performance of classical music is held in such spaces the sound lacks depth, making it difficult for the performers and audience to enjoy the sound. An AFC Enhance system can create an ideal sonic environment without the need for structural renovations.
*The name of AFC4 has changed to AFC Enhance.
AFC Enhance OFF
Not suitable for musical performance
(Minimal reverberation)
AFC Enhance ON
Ideal for musical performance
(Increased reverberation)
How AFC Enhance Works
AFC Enhance controls the acoustic environment via multiple microphones and loudspeakers strategically located throughout the space. This type of system generally employs one of the two following methods.
- “Regenerative approach” uses acoustic feedback, reproducing the sound picked up by the microphones via the loudspeakers and then picking up that sound affected by the room’s acoustics once more, thereby creating an acoustic “loop” that amplifies the room’s acoustic energy.
- “In-line approach” uses convolution signal processing to add a variety of synthesized reflected sound data (measured impulse responses) to the sound picked up via the microphones, to create the desired sonic environment.
AFC Enhance is a hybrid system that employs both of these methods. Through detailed control of reverberation and early reflections that have a profound influence on auditory impression, the sound propagating throughout the room can be adjusted as required while retaining the natural acoustic properties of the room’s structure.
AFC Enhance System Configuration
SK-AFC406 Block Diagram
Specification
Key Technologies
EMR: Switching Function for Stability
AFC Enhance employs a feedback loop for acoustic control. For optimum effect it is necessary to feed back as much energy as possible, but the more energy is fed back the higher the risk of uncontrolled feedback becomes. To keep the feedback loop under control at all times, the AFC Enhance system uses EMR (Electronic Microphone Rotator) technology to apply time variation, evenly distributing the loop’s frequency characteristics for dramatically increased howling resistance. EMR: System output is time-shifted to evenly distribute the feedback loop’s frequency characteristics. At any point in time the inputs are aligned with one of the outputs while the other outputs remain independent. The move from channel to channel is accomplished smoothly along with amplitude modulation (the allocation ratio for each channel remains constant).
*EMR is a patented Yamaha technology.
FIR Filters
The latest AFC Enhance system features much higher-density FIR processing power than previous versions so that extremely natural-sounding detailed reflection sound can be achieved even in dead spaces that have very little natural reverberation: Up to 10.666 sec at 48kHz / 5.333 sec at 96kHz.
