Measuring Noise and SNR

A-Weighted Filter

5 pF

Sound Pressure Level

Absolute

Sound

Pressure

(dB Pa)

–94 dB

Sensitivity

(dBV/Pa)

Voltage

(dBV)

Sound

Pressure

(dB SPL)

TLV1018

The overall noise of the TLV1018 is measured within the frequency band from 10 Hz to 22 kHz using an

A-weighted filter. The input of the TLV1018 is connected to ground with a 5-pF capacitor.

Figure 3. Noise Measurement

represents a sound pressure level (SPL) of 94 dBSPL. No input capacitor is connected.

The volume of sound applied to a microphone is usually stated as the pressure level with respect to the threshold

of hearing of the human ear. The sound pressure level (SPL) in decibels is defined by:

To calculate the resulting output voltage of the microphone for a given SPL, the sound pressure in dBSPL needs

to be converted to the absolute sound pressure in dBPa. This is the sound pressure level in decibels, which is

referred to as 1 Pascal (Pa).

The conversion is given by:

dBPa = dBSPL + 20 log 20

µPa

dBPa = dBSPL – 94 dB

Translation from absolute sound pressure level to a voltage is specified by the sensitivity of the microphone. A

conventional microphone has a sensitivity of –44 dBV/Pa.

Figure 4. dBSPL to dBV Conversion

Example: Busy traffic is 70 dBSPL

Copyright © 2008, Texas Instruments Incorporated

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