National Semiconductor recently announced the first in a line of audio products incorporating far-field noise suppression technology.
This unique technology delivers more natural-sounding voice quality by eliminating the output frequency distortions and other audio artefacts common with digital signal processor (DSP) or microprocessor software-based systems that use sub-band frequency processing algorithms to implement noise suppression.
The PowerWise LMV1088 dual-input microphone array amplifier reduces background noise and improves voice communication clarity in mobile phones, two-way radios and powered headsets. Part of National's PowerWise energy-efficient family, the device consumes only 1 mA.
The amplifier improves the talker's voice-signal-to-background-noise ratio in the communications system while retaining natural speech quality. Additionally, this allows increased accuracy by voice recognition systems since the background noise is not a significant part of the signal to discriminate against. The continuous-time analog processing provides instantaneous response to voice and background noise signals, unlike DSPs and processors which require extra computation time to adjust to voice background noise levels.
The LMV1088 is offered in a miniature 3,5 x 3,5 mm, 36-bump micro SMDxt package, with a power supply rejection ratio (PSRR) of 85 dB at 1 kHz, with a typical signal-to-noise ratio of 60 dB and less than 1% total harmonic distortion plus noise (A-weighted THD+N). It is designed for use with two microphones in an end-fire array configuration. The microphones can be spaced in a line 1,5 cm to 2,5 cm apart from each other, or the equivalent acoustic path distance. The optimal distance for the person speaking into the handset or headset microphone is 2 cm to 10 cm.
The amplifier's automatic calibration circuitry compensates for the microphone's gain and frequency response variations, eliminating the need to use expensive matched microphone sets, while allowing flexible placement of the microphones in the final product. The calibration data is stored in the LMV1088's internal EEPROM memory, and the calibration sequence chooses the optimised coefficients for the two microphones' spacing and acoustical environment. The chip features four I²C compatible, selectable operating modes: default noise reduction, microphone 1 pass-through, microphone 2 pass-through, and microphone 1 and 2 sum.
For more information contact Lambert Colyn, Arrow Altech Distribution, +27 (0)11 923 9600, [email protected], www.arrow.altech.co.za
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