So, if a digital microphone’s maximum SPL is 120 dB, then its sensitivity will be –26 dBFS (94 dB – 120 dB). As long as the full-scale digital word is mapped to the microphone’s maximum acoustic input (the only sensible mapping, really), the sensitivity must be simply the difference between this maximum acoustic signal and the 94 dB SPL reference. Sensitivity of a digital microphone is less flexible it depends on a single design parameter, maximum acoustic input. This sensitivity could be accomplished as long as the amplifiers, converters, and other circuits could support the required signal levels. Although it may not be practical for most designs, there is no physical reason why an analog microphone couldn’t have 20 dBV sensitivity, with a 10 V output signal for a reference-level input signal. For an analog microphone with a voltage output, the only limit to the size of the output signal is the practical limit of the system’s voltage supplies. The difference in units points to a subtle contrast in the definition of sensitivity of digital microphones compared to that of analog microphones.
#Sound reference pressure full
The sensitivity of digital microphones, with units dBFS (decibels with respect to digital full scale), is not so straightforward. Analog microphone input signal chain with preamp to match microphone output level to ADC input level. For example, an ADMP504 with 0.25 V maximum output voltage could be matched to an ADC with 1.0 V full-scale peak input voltage by using a gain of 4 (12 dB). Figure 1 shows how the microphone’s peak output voltage (V MAX) can be set to match an ADC’s full-scale input voltage (V IN) with a gain of V IN/V MAX. Given this information, with the appropriate preamplifier gain, the microphone signal level can be easily matched to the desired input level of the rest of the circuit or system. Where Output AREF is the 1000 mV/Pa (1 V/Pa) reference output ratio. For an analog microphone, sensitivity, in linear units of mV/Pa, can be expressed logarithmically in decibels: Typically specified in logarithmic units of dBV (decibels with respect to 1 V), it tells how many volts the output signal will be for a given SPL. The sensitivity of an analog microphone is straightforward and easy to understand. This reference point is but one characteristic of the microphone, by no means the whole story of its performance.
The magnitude of the analog or digital output signal from the microphone with that input stimulus is a measure of its sensitivity. Microphone sensitivity is typically measured with a 1 kHz sine wave at a 94 dB sound pressure level (SPL), or 1 pascal (Pa) pressure.
#Sound reference pressure how to
This article will discuss the distinction in sensitivity specifications between analog and digital microphones, how to choose a microphone with the best sensitivity for the application, and why adding a bit (or more) of digital gain can enhance the microphone signal. Mapping units in the acoustic domain to units in the electrical domain determines the magnitude of the microphone output signal, given a known input. Sensitivity, the ratio of the analog output voltage or digital output value to the input pressure, is a key specification of any microphone.
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