When dealing with analog audio, there are a few signal levels to be aware of: mic level, instrument level, line level (consumer), line level (professional), and speaker level. It’s critical to know the differences between these nominal signal levels when working with microphones and other audio equipment.
Do microphones output line level signals? No, microphones output audio signals in the mic level range and not in the line level range. Mic level is much lower than line level and so mic signals require amplification for use in other audio equipment. Mic preamps provide gain, boosting microphone signals from mic level to line level.
Let’s discuss what mic levels are why microphones output mic levels. In this article, we’ll also compare the various types of analog audio levels.
What Is Mic Level And Why Do Microphones Output Mic Level Audio?
Let’s answer each of these questions separately.
What is mic level? Mic level is the typical and expected analog audio signal level of professional microphone outputs and mic preamplifier inputs. Nominal mic level is generally between 1 to 100 millivolts AC (-60 to -20 dBV). Mic level signals need amplification to reach line level for use in mixing consoles and DAWs.
Mic level is much lower than line level (nominally one hundredth or one thousandth the signal strength). Line level is the nominal level for audio recording, reinforcement, and playback. So we need to boost the outputted microphone signal from mic level to line level for proper use in any type of audio recording/mix/reproduction.
Why do microphones output mic level? Microphones produce audio signals as their diaphragms move in reaction to sound waves. Because the diaphragm movement is relatively small, microphones are only capable of producing small mic level AC voltages. Some mics include internal preamps to boost their signals, but still output at mic level.
Microphone capsules simply cannot transduce line level signals. This is mostly due to the following factors:
- Microphone diaphragms are small and have limited movement.
- Varying sound pressure can only affect the mic diaphragm so much.
- The inefficiencies of microphone transducer principles (electromagnetic or electrostatic)
So now that we have an understanding of mic level and why microphones output mic level signals, let’s compare mic and line levels.
Comparing Mic And Line Level
So we’ve covered that mic level signals are much weaker than line level signals. We’ve also discussed that microphones output mic level signals but practically any audio recording, mixing, or reproduction is done at line level. That sums up the major differences between mic and line level, but there’s more to add to the comparison.
Line level electrical signals have a nominal value of 1 volt or 1 dBV. Mic levels, on the other hand, have greater variance. Though mic levels are often said to occupy the region between 0.001 V (-60 dBV) and 0.100 V (-20 dBV), some mic signals are much stronger than that, even at reasonable sound pressure levels (and especially when capturing loud sound sources).
The variations in mic level happen due to two main factors:
- Sound pressure level (SPL) at the microphone capsule: This represents the strength of the sound wave at the microphone’s diaphragm. Stronger sound waves have higher SPL values (measured in dB SPL) and move the microphone’s diaphragm greater distances. This results in the production of a stronger audio signal via the microphone transducer.
- Microphone sensitivity: Mic sensitivity is the relationship between the SPL at the mic diaphragm and the signal strength at the mic output. It tells us how sensitive the mic is as atransducer. Output sensitivity ratings are typically tested with a 94 dB SPL (1 Pascal) 1 kHz tone at 1 meter from the capsule.
For more information on microphone sensitivity, check out my article What Is Microphone Sensitivity And Why Does It Matter?
So mic level has a lot of variance. Let’s consider an example with two different mics capturing two different sound sources.
First, we’ll consider a Royer R121 ribbon microphone recording a voiceover.
Royer Labs is featured in My New Microphone’s Top Best Microphone Brands You Should Know And Use.
- The Royer R121’s sensitivity rating is -47 dBV/94 dB SPL or 4.5mV/Pa.
- Conversational voice happens at roughly 60 dB SPL (0.02 Pa).
The above scenario would yield an output signal strength of 0.09 mV or -80.9 dBV. This is extremely low even for a mic level signal.
Next we’ll consider a Rode NT1-A recording a trumpet.
Rode is featured in My New Microphone’s Top Best Microphone Brands You Should Know And Use.
- The Rode NT1-A’s sensitivity rating is -31.9 dBV/94 dB SPL or 25.4mV/Pa.
- Trumpets, at one meter distance can get as loud as 124 dB SPL (31.7 Pa)
The above scenario would yield an output signal strength of 805 mV or -1.88 dBV. This mic level signal is close enough to nominal line level that it likely wouldn’t need any amplification for use in line level equipment.
This is all to say that line level is nominal, whereas mic level varies quite a bit. Line level is something we strive to achieve within most audio equipment while mic level is simply the signal level that comes out of microphones.
Another important piece of information I should mention is the difference between professional line level and consumer line level (thus far we’ve been discussing professional line level).
Consumer line level is defined as having a nominal signal strength of -10dBV (316 mV). It is the nominal audio level in consumer audio devices (CD players, DVD players, etc.).
Professional line level is defined as having a nominal signal strength of +4 dBu or 1.78 dBV (1.23 V). As previously mentioned, it is the audio level in professional audio devices (signal-processing equipment, pro mixing consoles, etc.). Professional line level is outputted by professional line level devices and is expected by line inputs and audio power amplifier inputs.
Note that the above examples are simply examples to show the variation in mic level signals. Although you could achieve good results, I am not suggesting that you record voiceover with a Royer R121 nor that you record trumpet with a Rode NT1-A. In fact, I’d suggest using the R121 on trumpet and the NT1-A on voiceover.
How Are Microphone Signals Used In Line Level Equipment?
As mentioned, mic level signals need amplification before they are able to be used in line level equipment. This is achieves with microphone preamplifiers.
What is a microphone preamplifier? A mic preamp is an amplifying device that boosts a mic level signal at its input with enough gain to make the signal useful in line level equipment. Mic preamps “pre-amplify” a mic signal up to line level before that line level is further amplified to speaker level for reproduction in loudspeakers.
Microphone preamps are included in the design of most audio mixers, recorders, or interfaces. The preamps are built-into the mic inputs of these devices. Alternatively, mic preamp are also available as standalone units.
Active microphones (like the aforementioned NT1-A) have built-in preamp circuits. The preamps help to boost the signal and adjust the signal impedance. Active mics still do benefit from external mic preamps since they rarely output signals are nominal line level.
Finding devices with quality preamps should be a priority. Clean gain is important for preserving the true character of the microphone when boosting it for use with line level equipment.
Why Aren’t Microphones Designed To Output Line Level?
If you’ve made it this far, you must be thinking “why don’t microphone manufacturers put stronger mic preamps inside their microphones and have them output line level signals?”
I’ve thought the same thing too. It’s totally possible for microphone manufacturers to start building custom-made preamps that fit within the bodies of their microphones, allowing the mics to output line level signals. I remember asking a mentor this very same question.
Much of it comes down to economics and “tradition.”
The need for microphone preamps keeps preamp manufacturers in business.
With so much gear out there and so much vintage gear, it makes sense to continue doing things the same way so that audiophiles may continue their experimentation with microphone and preamp combinations.
Another reason could be that custom-made built-in preamps inside microphones would likely drive up the price of microphones and perhaps there simply isn’t a market for these types of mics.
What is the difference between mic and line level inputs? Mic and line inputs differ by the audio signal level they are designed to work with. Mic inputs expect mic level signals and line inputs expect line level signals. Sending mic level to a line input yields a very quiet signal whereas sending line level to a mic input would likely overload the input.
Can you plug a microphone into a line input? Yes, although it’s not recommended. Line inputs expect line level signals, which are much stronger than the mic level signals outputted by a microphone. Plugging a mic into a line input yields a very low level signal that requires a lot of gain and has a terrible signal-to-noise ratio.