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

  • AFC Enhance OFF

Not suitable for musical performance

(Minimal reverberation)

AFC Enhance ON

  • AFC Enhance ON

Ideal for musical performance

(Increased reverberation)

How AFC Enhance Works

How AFC Enhance Works
Regenerative approach / In-line approach

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

AFC System Configuration

SK-AFC406 Block Diagram

SK-AFC406 Block Diagram


AFC Enhance
Software SK-AFC406/SK-AFC404/SK-AFC402 (There are three SKUs to be selected depending on the size of the system).
Processing Engine As for specification, please contact your local Yamaha representative for details.
Inputs 32 microphones, 24 AUX
Outputs 96
Sample Rate 48kHz, 96kHz
Dante I/O 128ch (with AIC128-D Dante Accelerator)
Control devices ProVisionaire Control, ProVisionaire Touch, MCP1

EMR: Switching Function for Stability

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

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.

AFC Enhance Patent List

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