BLAcoustics NMC DSP Noise Masking Controller V2
The Noise Masking V2 is a dual channel DSP noise masking controller in a 19” rack mounting chassis. It contains a multi-function digital processor featuring analog noise input and PA input mixing, capable of transforming any Public Address or Voice Alarm system into a combined PA/Noise Masking system. Provided with a 32 bit, 147 MHz clock speed DSP as well as 24 bit A/D and D/A converters, the unit is controlled by software to fine tune the noise curve required for the target area. There are four separate noise channels that each have independently adjustable cross-overs and 32-band equalization, all adjustable via the PC control software.  There are also two analog inputs that can be used for PA mixing from the host PA or VA system.  PA Input 1 mixes audio with noise channels 1 and 2, while PA Input 2 mixes audio with noise channels 3 and 4. The Noise Masking V2 unit also allows for attenuation of the noise signal during PA announcements. When an announcement is detected the noise dips to a low level so that it doesn’t impede the intelligibility of the PA audio.  Once the announcement has finished, the noise level slowly recovers to its pre-set level. This slow restoration of noise keeps the presence of noise discrete and in-discernible to the occupants of the target area. The unit consists 3 main sections:
  • Transformer isolation and mixing
  • Noise generator and VCA
  • DSP Audio processor
The audio transformer isolation module consists of line level transformers that provide isolation and also balances the input and output feeds. The noise generator board produces a low level random analog signal.  The signal is a broadband noise signal limited only to the 20Hz to 20kHz audible range.  This board also takes the PA input from the isolating transformers which is rectified and applied to a voltage controlled amplifier which in turn adjusts the output of the noise generator negatively – providing the attenuated noise adjustment during PA announcements.  Adjustments are available on the board that allows adjustments to the sensitivity and the attack time of the VCA, as well as a general volume level for the noise outputs. The DSP audio processor features a 32 bit Cirrus Logic (Clock speed: 147 MHz) Digital Signal Processing chip and A/D / D/A converters working in PCM at 48 kHz with 24 bit resolution. The processor speed allows the installer to hear and verify in real time the changes applied during the equaliser adjustments.  The board has volume adjustments for each of the two noise inputs.  The software can be used on-site with a laptop connected via the front-panel USB connector to make the necessary adjustments to the noise curve.  Equalisation is via a 31-band graphic equalizer (1/3 Oct.; ±12 dB) for each output channel. The set-up and commissioning of this equipment must be carried out by a suitably qualified electro-acoustic engineer with appropriate knowledge of the associated equipment and acoustic properties of the target areas.  It is recommended that a Type I SPL and Audio Analyser be used when commissioning.
Noise Masking
Noise Masking

The principle of ‘Noise Masking’ involves the production of a noise that effectively competes with other noises that are recognised as an annoyance to the recipient. Noise Masking, often referred to as ‘Sound Masking’, is an important component of creating a comfortable working environment in office areas.