This topic covers configuring the ANC-1 device, however, if you’re looking for information on the hardware or the software configuration dialogs then please refer to the relevant section.
Please note that the values and settings suggested are a good initial guide however are primarily for example purposes. Exact settings should be tailored for each unique application.
First off in the ANC-1 Audio & Live Control tab we need to configure Microphone gains. Enable the first microphone and phantom power if it’s required. Increase the Microphone 1 gain until the meter is averaging around -50dB. The gain should be set when the Noise Floor is at its lowest, which would most likely be when the room is empty. If you’re using both microphone inputs on the ANC-1 you’ll also need to set the gain on the second one independently. Using the checkbox, disable Microphone 1 and Enable Microphone 2. Increase the gain until you’re averaging -50dB on it as well. After the correct levels have been reached enable both microphones again.
Although there’s two physical microphone inputs on a single ANC-1, only one microphone is required for the Ambient Noise Compensation to work. One microphone would be sufficient for a medium sized foyer, however using the example of a long corridor, having two sense points would be better than one. Once both microphones are enabled at the same time, the audio signals are summed and the average of both used.
For the majority of installations setting the Ambient Threshold to +10dB above the noise floor should be a sufficient value. The Ambient threshold is the level in dB that the Noise Compensation will start to engage. In the real world this means once a person enters the currently empty acoustic space they can make up to 10dB above the rooms noise floor before the Paging and background music levels will begin to be increased.
The RT60 value is a measurement how long it takes sound to decay 60dB within the rooms acoustic space. The default is 1000ms and typically this would be about the value of an office space, foyer or a corridor area. A concert hall would be around 2000ms, and an empty convention Centre typically around 5000ms.
The Maximum and Minimum compensation fields are used to enter a value in dB for the maximum, or minimum gain applied to the program source. For this example I want my theoretical room to increase from 0dB to a maximum of 10dB and no louder so I would configure the values to 0dB and +10dB respectively.
The Ratio dropdown is used to
specify the proportion which the level will be raised in regards to the
ambient level. This means for every +1dB increase within the acoustical
space, the program source increases by the value selected in the drop
down. So say I select .25, for every extra 1dB of noise in the room, the
output level of the Zone will increase by a quarter of a dB.
In the Advanced tab, the Noise Floor Ambient Setting is expressed in dB and allows the expected noise floor level to be set. The noise floor should be 10-20 dB below the microphone sense level to ensure the algorithm is working optimally. Considering we set the microphone gain so the sense level was around -50dB earlier, the default value of -60 for the noise floor will be sufficient.
The values entered in to the Compensation field relate to the amount of time over which the gain is altered. A train station requires very fast changes when a train arrives or passes through a station however a convention center only requires gradual changes as it slowly fills up.
The Maximum Gain Adjustment Rate, both up and down, defines by how much gain can be added or reduced in one second and the response time is used to specify how quickly the compensator reacts to the ambient noise increasing in the room.
For example the train station would use high gain Adjustment Rates, say 8dB/s and a quick response time, around 500ms.
The convention center however would use low gain Adjustment Rates, say 2dB/s and a slow response time, around 300,000ms (5 minutes).