Ralph Jones
2018-08-17 21:55:36 UTC
There’s been some interesting discussion here about Micro-ElectroMechanical Systems (MEMS) microphones for ambisonic mic arrays. These devices seem to offer some compelling qualities (particularly small size and low cost) but their signal-to-noise spec is 65 dBA. Some folks posting here have seemed to suggest that this level of noise might possibly be acceptable.
IMHO, based on decades of experience, a microphone with a signal-to-noise ratio of 65 dBA is useless for professional recording. That's in the SNR range typical of consumer cassette tape machines or analog AM radio.
For comparison, consider that professional large-diaphragm condenser mics achieve 120-130 dB SNR. The Sennheiser Ambeo has an SNR of about 110 dB. Portable digital audio recorders and popular audio interfaces make about 100 dB, and Red Book CDs 98 dB. Even vinyl records are about 6 dB quieter than MEMS mic elements.
Put a MEMS mic at the input of a digital recorder and you’re wasting 35 dB of dynamic range (not to mention the case of using several of them in an ambisonic array). That’s huge. A symphony orchestra playing at mezzoforte or louder may mask the noise if the mic is reasonably close to the stage, but forget trying to record softer passages. Recordists trying to capture natural ambiences will be sorely disappointed; a lot of what they’re trying to record will simply disappear into the noise floor. You might get away with using it for non-critical functions like background crowd noise for telecasts of sporting events, but that’s about it.
MEMS mics appear to me to have been developed for applications that require very small size, physical ruggedness, reasonable frequency response and low cost, but can tolerate a high noise floor. There are lots of such use cases, but professional audio is not one of them. If we wish to advance the art of ambisonic recording and reproduction, we cannot compromise basic performance specifications for the sake of a trendy idea.
Ralph Jones
IMHO, based on decades of experience, a microphone with a signal-to-noise ratio of 65 dBA is useless for professional recording. That's in the SNR range typical of consumer cassette tape machines or analog AM radio.
For comparison, consider that professional large-diaphragm condenser mics achieve 120-130 dB SNR. The Sennheiser Ambeo has an SNR of about 110 dB. Portable digital audio recorders and popular audio interfaces make about 100 dB, and Red Book CDs 98 dB. Even vinyl records are about 6 dB quieter than MEMS mic elements.
Put a MEMS mic at the input of a digital recorder and you’re wasting 35 dB of dynamic range (not to mention the case of using several of them in an ambisonic array). That’s huge. A symphony orchestra playing at mezzoforte or louder may mask the noise if the mic is reasonably close to the stage, but forget trying to record softer passages. Recordists trying to capture natural ambiences will be sorely disappointed; a lot of what they’re trying to record will simply disappear into the noise floor. You might get away with using it for non-critical functions like background crowd noise for telecasts of sporting events, but that’s about it.
MEMS mics appear to me to have been developed for applications that require very small size, physical ruggedness, reasonable frequency response and low cost, but can tolerate a high noise floor. There are lots of such use cases, but professional audio is not one of them. If we wish to advance the art of ambisonic recording and reproduction, we cannot compromise basic performance specifications for the sake of a trendy idea.
Ralph Jones