In microphone specifications, the signal-to-noise ratio (SNR) is defined as the ratio of the output level produced by a standard reference sound pressure to the output in the absence of any sound. Which reference pressure (in pascals) is commonly used in this definition?

Introduction / Context:
Signal-to-noise ratio (SNR) for microphones quantifies how much usable signal is obtained relative to internal self-noise. A consistent reference sound pressure is required so manufacturer ratings are comparable across devices and datasheets.

Given Data / Assumptions:

• We need the standard reference sound pressure used to define SNR in many practical microphone specs.
• The options are 0.5, 0.2, 0.1, and 0.01 Pa (pascals).

Concept / Approach:

Common industry practice uses a fixed reference tone and level. While 1 Pa corresponds to 94 dB SPL and is widely used for sensitivity ratings, many SNR expressions in practice also cite 0.1 Pa (≈ 74 dB SPL) as a lower-level reference to highlight usable output above self-noise for typical conversational levels. Given the provided options, 0.1 Pa is the most standard among them for such SNR definitions in basic question banks.

Step-by-Step Solution:

Verification / Alternative check:

Manufacturers often provide both sensitivity at 1 Pa (94 dB SPL) and self-noise in dBA; SNR can be extrapolated at alternate reference levels such as 0.1 Pa. Of the choices offered, 0.1 Pa is the accepted value in many exam contexts.

Why Other Options Are Wrong:

• 0.5 Pa and 0.2 Pa: Higher than typical reference used in such SNR questions.
• 0.01 Pa: Very low (≈ 54 dB SPL), not the standard teaching reference here.
• 1.0 Pa: Common for sensitivity, but not among the provided answer set in this question.

Common Pitfalls:

Confusing microphone sensitivity reference (often 1 Pa) with the SNR reference used in particular problem sets. Always check which reference the question expects.

Final Answer:

0.1 Pa