ARCHITECTS & ENGINEERS SPECIFICATIONS
The ambient noise compensation device shall automatically regulate the operating level of the sound system in response to fluctuating noise levels in the system's operating area. In this way the audio programme shall always be at a preset level - background or foreground - relative to the ambient noise. In foreground mode, the programme shall always be audible and intelligible without ever being too loud.

The device shall employ digital signal processing circuitry and be capable of compensating for pre-set levels of ambient noise fluctuation, up to a maximum of 31dB. The device shall continuously measure the true signal-to-noise ratio taking into account programme level, frequency spectrum and statistics as well as ambient noise level, frequency spectrum and statistics - both as sensed in the sound field so as to incorporate the effects of the signal path and room acoustics. These signal and noise data shall be processed in real time, by an ear-brain model to determine the subjective impact on intelligibility and audibility as perceived by the ear. A variable fast response time shall ensure that signal level changes are not audible. The unit shall incorporate an independent sensing microphone, located within the sound field to be affected, and not in any way isolated from the loudspeakers it controls.

The device shall be continuously adaptive (self-calibrating),neither requiring calibration at the time of installation nor at any time thereafter, thus allowing complete freedom in changing the operating parameters of the sound system, such as amplifier settings, loudspeaker locations, etc. without operator intervention. Adaptation shall be accomplished by using only the source signal without any tones or test signals.

The device shall have inputs and outputs that are switchable between balanced and unbalanced and the unit shall have an option for a paging input. In addition to the various functions and general specifications mentioned above, the ambient noise compensation device shall meet or exceed the following overall performance criteria.

Frequency response : 50Hz to 100Hz +0/-0.5dB. 
Signal to noise plus distortion ratio : 80dB
Minimum input impedance : 10kOhms

The device shall be housed in a one rack unit high enclosure, 19.0" / 48.26 cms wide by 4.12" / 10.46 cms deep. The ambient noise compensation device shall be Audiostat™ DSS MC11 R .

(Also available in a desk-top version : DSS MC11 D)