A breakthrough innovation in sound sensing from STMicroelectronics

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Dynamic Range and AOP

• The dynamic range is the difference between the minimum and maximum detectable sound by the microphone without distortion:

• The maximum signal that the microphone can “listen” without distortion is also called acoustic overload point (AOP). For both analog and digital ST microphones the AOP is 120dBSPL as sound pressure

• The minimum signal that a microphone can “listen” depends on its SNR. In other words, the minimum signal is equivalent to the residual noise in terms of dBSPL

Frequency response

The frequency response of a microphone in terms of magnitude:

• Indicates the sensitivity variation across the audio band. Or even, this parameter describes the deviation of the output signal from the reference 0dB

• Typically the reference for this measurement is the exactly the sensitivity of the microphone  0dB = 94dBSPL @ 1kHz

• The typical frequency response of a microphone shows a roll-off at low frequency due to ventilation hole and an rise up at high frequency due to Helmholtz effect

• The frequency response of a microphone in terms of phase:

• Indicates the phase distortion introduced by the microphone. In other words the delay between the sound wave moving the microphone membrane and the electrical signal at the microphone output

• This parameter includes both the distortion due to the membrane and the ASIC

ST's MEMS microphone offers best acoustical performances - best frequency response, Omni-directional polar pattern, best sensitivity , reduced phase rotation, Optimized audio quality (SNR > 60dB), Precise unit-to-unit-matching. It also offers Highest reliability and robustness, Superior stability of humidity, temperature and dust parameters.

Directional acoustic patterns using MEMS Microphone

An omnidirectional microphone response is generally considered to be a perfect sphere in three dimensions. The smallest diameter microphone gives the best Omni-directional characteristics at high frequencies. This is the reason that makes the MEMS microphone the best Omni-directional microphone

But MEMS Microphone can also be used in array to modify the response according to desired acoustic patterns

The physical and acoustic parameters of ST's MEMS microphones perfectly fit the challenging requirements of distant-speech interaction systems. The small form factor allows the researchers to easily embed entire arrays of microphones in the walls, desks, or speech-enabled appliances of the automated home, while the microphones’ excellent acoustic characteristics, coupled with sophisticated signal-processing technologies, will make it possible to identify and capture an individual speaker from several meters away, in a crowded room with music playing.

The distant-speech interaction capability will not only dramatically change the way people interact with technology, but can make a real difference for those who can’t easily move around, such as the elderly or the motor-impaired. In addition to the home scenarios, the distant-speech interaction systems can find use in robotics, tele-presense, surveillance and industry automation.

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