DocID026988 Rev 1

3/12

AN4598

Output signal amplitude and gain setting

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Output signal amplitude and gain setting

The analog signal on the output of the microphone contains the audio signal plus some

noise.

The amplitude of the audio output signal depends on the acoustic pressure.

MP23AB02B datasheet and is calculated using Equation 1.

Equation 1

In terms of scale, 20 µPa is the minimum level of hearing, while talking produces an acoustic

pressure around 20 mPa. Acoustic pressure can also be expressed in dB SPL (sound

pressure level) where: dB SPL

The acoustic and electrical relationships of the MP23AB02B are illustrated in Figure 1.

Figure 1. Acoustic and electrical relationships of the MP23AB02B

Note that acoustic pressure drops with distance from the source.

Assuming free field conditions, if we double our distance from the source, the acoustic

pressure is divided by:

•

2 if the source is considered to be a point like a speaker (i.e. -6 dB SPL)

•

√2, if the source is considered to be a line such as a road (i.e. -3 dB SPL)

Knowing the acoustic pressure applied to the microphone and the desired amplitude after

the amplification stage tells us how much the gain should be.

10

20

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