It's a pity that so many wrong or misleading information on digital microphones are distributed. Let's try to bring some facts into that discussion:

  • Do digital microphones have a higher noise floor than analog microphones?

No. In a digital microphone there are A/D converters and an analogue preamp stage - just as it is the case in a signal chain using an analogue microphone.

In both cases a bad matching leads to higher noise, because the noise of the elctronic circuit superimposes the thermic noise of the air particles on the membrane. In a digital microphone this matching is done by the microphone manufacturer. With an analogue microphone, the sound engineer has to take care of the optimal matching. "Optimal" matching means that the preamp and the A/D converter gains are high enough so that no noise of these devices is added to the microphone's self noise. When this is successful (what is normal), the noise of both digital and analogue microphone is the same.

The only remaining difference regarding the minimum self noise is in the quality of the utliized devices. The microphone transducer element is the same in both cases - the other devices are not. In the digital microphone the devices need to be small and power-efficient, which is no advantage but also not necessarily a disadvantage, because a higher noise floor can be masked with a higher device gain. 

--> see  AES 42 White Paper chapter 2.2 and 2.3

Equivalent noise level (self noise) of some analogue and digital microphones:

Microphone model analogue/digital    

Equivalent self noise

  

Analogue model

Digital model

Neumann KMA 133/KMD 133 (Omni) 15 dB(A) 15 dB(A)
Neumann KMA 184/KMD 184 (Cardioid) 13 dB(A) 13 dB(A)
Neumann TLM 103/TLM 103 D (Large-Membrane Cardioid)  7 dB(A) 7 dB(A)
SCHOEPS CMIT/SuperCMIT (Shotgun) 14 dB(A) 16 dB(A)
Sennheiser MKH 8060/MKH 8060 + MZD 11 dB(A) not stated, >=11 dB(A)
     
  • Can digital microphones achieve a higher dynamic range than analogue microphones?

The correct question has to be: Can a signal chain using a digital instead of an analogue microphone achieve a higher dynamic range? ("more dynamics" means: not only the noise floor is low, but the MaxSPL is high at the same time)

Answer: the signal cahin using a digital microphone can achieve the high dynamic range more easily. The dynamis of the analogue signal chain depends on the type of the used devices and their matching. An optimal signal chain consisting of an analogue microphone, a multi-stage preamp and A/D-converter can reach the same high dynamics or even more. If the preamp is single stage only (more common), a high SPL can be accepted only with a low gain leading to a higher noise floor. If never quiet and loud signals occur at the same time, this is no problem. If they occur at the same time, the single stage architecture has a significant disadvantage.

Example 1: Organ recording at night. The organ can produce signals at very high and very low SPLs. If the organist plays a pianissimo-passage, the self noise needs to be low and thus the gain high. If the organist now plays a fortissimo-passage, the gain needs to be changed in order to prevent overloading or you simply need to use a multi-stage preamp and A/D converter.

Example 2: Location sound recording at a very quiet film location. Location recordists need to be aware that very sudden loud sounds during a quiet dialogue can occur like the noise of a smashed closing door. This leads to overload using a normal preamp.

--> see AES 42 White Paper chapter 2.2 and 2.3

Multistage preamp and A/D converter architecture:
A Multistage preamp and A/D converter architecture means the same as if the sound engineer would split the microphone signal and lead it to two preamp channels with different gains. The channel with the high gain is used with quiet signals and the channel with the low gain is used with loud signals.
The choice of the preamp channel is done automatically when using a Multistage preamp and A/D converter architecture. The switching is not audible due to the modern, advanced technology of todays' architecture. These multistage systems are called e.g. "Gain-Ranging". A very similar technology is used in the Neumann digital micropohones using a different analogue gain function.

 

  • Do all digital microphones have a high dynamic range?

No. At the moment, only microphones of the Neumann Solution-D series have a high dynamic range. The other existing digital microphones/amplifiers (Sennheiser MZD8000 und SCHOEPS SuperCMIT) are single stage and thus have a lower dynamic range.

  • Do you need a gain in a digital microphone?

No. Analog microphones preamps need gain to correctly adjust the microphone level to preamp and A/D converter. In a digital microphone this adjustment is fixed and not changeable. Thus, the gain in a digital microphone simply decreases the dynamic range by lowering the maximum allowed SPL.
However, a digital gain in or after the digital microphone is useful to shift the microphone level to normal working level.