Audio intelligence with Praesensa

Issue 4 2021 CCTV, Surveillance & Remote Monitoring

Praesensa was launched at the end of 2019 to offer quality, security and reliability in public address and voice alarm (PA/VA) systems. The latest addition to the family is the Praesensa Ambient noise sensor, particularly relevant for applications such as campuses, shopping malls, airports, railway terminals, factories and more.

The loud buzz of a crowd, the passing roar of vehicles or the hum of equipment can affect the intelligibility of voice messages. Similarly, music or messages can cause discomfort when they are played too loudly in a quieter building. Automatic Volume Control (AVC) technology helps to deal with these ambient noise changes. AVC – also known as Noise Dependent Volume Control (NDVC) – changes the loudspeaker volume according to the ambient noise levels and automatically solves the dilemma of a system being too loud in a quiet environment versus too soft in a noisy environment.

The new Praesensa Ambient noise sensor monitors the ambient noise level and alerts the system controller about changes. Announcements are then automatically adjusted to a comfortable level above the ambient noise to ensure intelligibility and background music is adjusted to maintain the right atmosphere.

Up to four sensors can operate together to cover a large area. In the event of a failure or disconnection of the device, the announcement volume is automatically set to its maximum within the applicable control range. This fail-safe ensures that the system will never interpret a missing sensor as a silent ambient level and decrease the announcement level mistakenly. The intelligibility of messages is ensured and the system remains safe.

For AVC actions to be discreet yet effective, its adaptation threshold, range, slope and speed can be optimally configured for a specific application and location. Furthermore, its behaviour is different for short announcements compared to ongoing background music. Sample-and-hold mode is used for live speech calls and playback of pre-recorded messages. The noise level is sampled and the latest level information is held and used during the call; this is not affected by the sound of the call itself or its associated reverberation and echoes. Tracking mode is used for background music; the ambient noise level is tracked, allowing the continuous adjustment of the background music’s volume to suit the environment.

The sensor is directly connected to the IP network – just one CAT5e cable can accommodate data exchange and power over Ethernet (PoE). The device communicates ambient noise level data directly to the Praesensa system controller, which adjusts the output level of the involved amplifier channels accordingly. Because only level information is exchanged and no audio data, the occupied network bandwidth for this function is minimised and there is no risk of audio eavesdropping.

A back box is included for mounting on solid ceilings and walls. Without the back box, the sensor can be flush mounted in hollow walls or suspended ceilings. The device is water resistant (IP54) with or without the back box and can be used indoors and outdoors. It comes with a black and white front cover for inconspicuous installation.


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