Yamaha AFC

AFC 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 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.

Regenerative approach

  • Yamaha AFC

In-line approach

  • Yamaha AFC

EMR: Switching Function for Stability

AFC 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 (howling) becomes. To keep the feedback loop under control at all times, the AFC 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.

Yamaha AFC

FIR Filters

The latest AFC4 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.

Yamaha AFC
Pat.No. Title Date of Pat. Contents
5,025,472 Reverberation imparting device 1991 Basic idea Feedback/FIR
5,131,051 Method and apparatus for controlling the sound field in auditoriums 1992 Energy exchange
5,642,425 Sound field control device 1997 EMR
6,072,879 Sound field control unit and sound field controll device 2000 YUME-HIBIKI including EMR & Fluc-FIR
6,157,724 Apparatus having loudspeakers concurrently producing music sound and ref 2000 Music instrument including EMR & Fluc-FIR
7,474,753 Sound field control apparatus, signal processing apparatus, sound field control program, and signal processing program 2009 Hardware Configuration