Connections
· Feed the "program" signal into the Program Input (top left) of the ANC block. Setup of the ANC block is best done with a relatively constant program source. This can be the actual program source or a pink noise approximation, but its level should represent the highest program material level you expect will be fed to the ANC block.
· Feed the "ambient" signal into the Ambient Input (bottom left, marked with an "A") of the ANC block. This signal should be derived from either a single dedicated sensing microphone, or from a dedicated array of sensing microphones feeding a common Mixer block. Setup of the ANC block is best done when the ambient noise in the room(s) is minimal, but the Ambient Meter should read at least -60dBu.
· Connect the output of the ANC block to its destination. Keep in mind that the ANC should be the last block in the program signal path, with no form of level control provided at the outputs, amplifiers, or speakers.
Setting Min and Max Gain
· Adjust the Min Gain and Max Gain settings for the desired amounts of minimum and maximum gain to be applied to the program signal. Remember that Min Gain is the constant gain that the ANC block will apply while the Ambient Input signal level is below the Ambient Threshold. Remember that Max Gain is the maximum amount of gain that the ANC block will ever apply to the program input.
If Min Gain and Max Gain are not known, these settings may be determined by listening to the ANC output, as follows:
· Set the Ambient Threshold to its maximum setting (+24dBu) to ensure the Ambient Input level is below threshold. This ramps the ANC to the Min Gain setting. Keep in mind that the speed of this ramping is determined by the Gain Time setting.
· Adjust Min Gain until you have the desired minimum program level comining out of the ANC block. Note this value for later.
· Adjust Min Gain until you have the desired maximum program level coming out of the ANC block. Set Max Gain to this value. Set Min Gain to the value determined in the previous step.
Setting Response Times
· Adjust the Gain Time to determine how quickly the ANC gain changes. Gain Time is the amount of time it takes for the ANC block to ramp from Gain Min to Gain Max, or vice versa.
· Adjust the Ambient Response time to determine how quickly the Ambient Input detector responds to changes in the Ambient Input signal. Ambient Response should be set fast enough to track important ambient level changes (e.g. an approaching train in a depot), but slow enough to ignore unimportant ambient level changes (e.g. someone popping their bubble gum).
Note: The overall responsiveness of the ANC output is determined by the larger (slower) of the two aforementioned times: Gain Time and Ambient Response time.
Setting Thresholds
· Press the "Set Threshold" button, ensuring that the Program Input level is a good approximation of the highest program signal level you expect will be fed to the ANC. This process records the levels of both the Ambient and Program inputs. The Ambient Threshold is set to 10dBu higher than the recorded Ambient level. This process takes up to 5 seconds.
Set Gain Ratio
· Adjust Gain Ratio to specify how many dB of gain is applied for every dBu over Ambient Threshold the Ambient level is.