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Glossary
 

Automatic volume adjustment

Description
Many accessible pedestrian signals have volume control that is automatically responsive to ambient (background) sound.
  • A louder signal is produced when vehicle and other noise at an intersection is high (as during rush hour or construction).
  • A quieter sound is produced when traffic volume is lower, (as during night-time hours).
  • A microphone continuously samples the noise levels and varies the volume in response to the existing sound levels.
  • The microphone may be incorporated into the pushbutton housing, or located at the pedhead.
Automatic volume adjustment is also known as automatic gain control (AGC), or ambient sound adjustment.

Additional information
Some signals can be pre-set to vary volume within particular ranges.
  • Most signals with automatic volume control have a minimum limit placed at about 30 dB and a maximum limit at about 90 dB.
  • A signal that is 2-5 dB above ambient sound, as perceived at the departure curb, is loud enough to inform pedestrians who are blind that the Walk interval has begun. If the microphone is installed at the pedhead, and the pedhead is set back from the curb, the volume as sensed by the microphone is not as loud as that perceived by pedestrians waiting at the curb. Therefore, at each installation, the setting must be adjusted depending on the location of the microphone in relation to pedestrians waiting to cross.
  • Some APS allow the installer to set the range of the locator tone and the WALK indication separately; others are set the same.
  • Some APS have adjustments for microphone sensitivity as well as volume.
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How used
Automatic volume adjustment provides flexibility and allows APS to adjust so they are not disturbing to neighbors. This is also helpful to blind or visually impaired pedestrians, as the APS does not drown out essential traffic sounds necessary for crossing.

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References
MUTCD 4E.06

Draft Public Rights-of-Way Accessibility Guidelines 1106.2.3.2, 2021.3.2,

PROWAAC X02.5.2.2G

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