Question: What is a microphone’s maximum input sound level, self-noise, signal-to-noise ratio and dynamic range, and why are these measurements important?
Answer: Microphone specifications were discussed a few weeks ago in our blog post “What Do Microphone Specifications Mean,” and we have since been asked, “Why are these measurements important?” They are important because they give the user an idea of how a microphone will perform, and can be helpful in determining if a particular microphone is right for a particular application. Below, we explain the importance of four specs: maximum input sound level, self-noise, signal-to-noise ratio and dynamic range.
Condenser and phantom-powered ribbon microphones have a maximum sound pressure level the diaphragm can withstand without becoming distorted. This measurement is referred to as maximum input sound level, often termed “max sound pressure level” or “max SPL.” Once a microphone element has reached this maximum level in dB, the microphone may begin experiencing problems from the total harmonic distortion (T.H.D.). Dynamic microphones do not have a max SPL rating due to the design and function of the dynamic microphone element. Loud applications such as percussion or distorted guitar amps may have transients that exceed the max SPL of a microphone. This is sometimes averted by engaging a pad, if available on the microphone.
The self-noise of a microphone is the amount of noise created by a microphone’s internal circuits. All circuits create a small amount of noise, and this specification may be commonly found with Audio-Technica condenser and phantom-powered ribbon microphones. Microphone self-noise is not heard in most recordings, but it may become a factor when recording low-volume sound sources. Therefore, when selecting a microphone for such low-volume applications, the self-noise spec will likely figure into the decision. A microphone with low self-noise is often chosen for broadcast, quiet, and critical recording applications, but for recording applications that require a large dynamic range, such as recording sounds from loud sources, low self-noise is not an issue.
The signal-to-noise ratio measurement utilizes the self-noise specification, expressing its correlation to the level of the desired signal. The dynamic range of a microphone identifies how much “head room” your microphone will have between the self-noise and the max SPL. Most microphones on the market today have a healthy dynamic range as microphone technology is getting better and better. The dynamic range measurement is found by subtracting the self-noise from the maximum input sound level.
The measurements reviewed here are often used in conjunction with each other, and they may all be used to “get an idea” of the characteristics and performance of a microphone. But remember to let your ears make the final decisions. If you have further questions, feel free to contact the Audio Solutions Department.