This page introduces automatic control of broadcast audio in environments where ambient noise levels vary.

In places such as stations and shopping malls, the number of visitors varies depending on the time of day, and the level of ambient noise changes accordingly. If the broadcast volume is fixed, it may sometimes be too low and buried in the ambient noise, while at other times it may sound unnaturally loud. A fully featured system can automatically adjust the broadcast volume in response to these changes. The following sections introduce two main methods.

​Methods

​Control Based on Sound Pickup

This method uses microphones to pick up ambient noise and adjusts the broadcast volume accordingly. In many cases, dedicated equipment is required to perform this type of control. In TOA systems, this function is available in the VX-3000 system and the CX-1000 system under the name ANC, or Ambient Noise Control.

Sensor Microphone
​The microphones used for sound pickup, sometimes referred to as sensor microphones, are usually installed on the ceiling. It is recommended that the microphones be installed in areas where users tend to gather. If they are installed in locations where people simply pass by, they may not pick up the ambient noise effectively. 
​Sensor microphones with higher sensitivity may be easier to adjust, but It is not always necessary for the sensor microphone to emphasize high-frequency sounds.​

Sensitivity of Volume Adjustment
There is no need to make the sensitivity excessively high or to change the volume frequently. Rather than responding to sudden noises, the system should be set with the idea of tracking broader changes in noise levels over a period of about an hour. A longer sensing time should be used, and gradual changes are preferable both when increasing and decreasing the volume.

Distinguishing Between Broadcast Audio and Ambient Noise

The ANC function of the TOA VX-3000 Series and CX-1000 Series introduced earlier can distinguish between broadcast audio and ambient noise. However, some products may not be able to distinguish between the two. In such cases, measures such as positioning the sensor microphone away from the loudspeakers are necessary so that the broadcast audio is less likely to be picked up by the sensor microphone.

This is because the broadcast audio may increase the sound level picked up by the sensor microphone, which then causes the broadcast volume to increase. The louder broadcast audio is then picked up again by the sensor microphone, creating a feedback loop that causes the broadcast volume to become progressively louder.

Volume Adjustment by Timer

This method changes the volume by using a timer at preset times. Although it does not allow for flexible adjustment like the sound pickup method, it can be used in cases where the timing of noise level changes is predictable. TOA's IP-A1 Series is equipped with this function.

​Areas Subject to Volume Adjustment

Some products, such as the IP-A1 Series, allow the volume to be adjusted for each individual loudspeaker. In many cases, however, the volume of multiple loudspeakers is adjusted together. The area over which the volume is adjusted at one time is an important consideration. In particular, when using a sensor microphone, the relationship between the microphone position and the target zone is important. Naturally, the microphone must be installed in a position where it can pick up the ambient noise in the target zone. Also, if you want to divide loudspeaker lines using a speaker selector (SS), please note that the volume will change for all loudspeakers connected downstream of the SS.

In the diagram above, “ANC” should be understood as the section that analyzes the sound picked up by the sensor microphone and adjusts the volume accordingly.