What’s the Difference Between Line and Mic Levels?

Are you confused by line level versus mic level? Well, you’re not alone. We’re often asked to explain the difference. Simply stated, these both refer to the voltage level of an audio signal.

Wired and wireless microphones are typically connected to mic-level inputs, whereas most other audio devices use line level. (We’ll get to instrument- and speaker-level signals in a minute.) The voltage of each signal type varies significantly, however, making it important to know how they differ.

What is mic level?

A mic-level or microphone-level signal describes the voltage generated by a microphone when it picks up sound, typically just a few thousandths of a volt.  This voltage varies in response to changes in sound level and distance. Of the four main types of audio signals, mic level is the weakest and requires a pre-amplifier to bring it up to line level. Microphone level is usually specified between -60 and -40 dBu. (dBu and dBV are decibel measurements relative to voltage.)

Several different types of devices are used to boost microphone levels to linelevel signals. Mixers are probably the most popular piece of equipment, since they can also combine multiple signals together into a single output. But preamplifiers and mic-to-line amplifiers do the job just as well and are available as single-channel or multi-channel devices.

What is line level?

 A line-level signal is approximately one volt, or about 1,000 times as strong as a mic-level signal, so the two do not ordinarily use the same input. This signal travels from your pre-amp to the amplifier that powers your speakers.

There are two standard line levels:

  • -10 dBV for consumer equipment (like MP3 and DVD players)
  • +4 dBu for professional equipment (mixing desks and signal processing gear)

The other two types of audio signals you’ll run into are instrument and speaker levels. Like mic-level signals, instrument-level signals (such as an electric guitar or bass) require preamplification to bring them up to line level. Post-amplification speaker-level signals are even higher in voltage than line level and require speaker cables for safe signal transfer.

Matching Levels

It’s crucial to match a device to the correct input, since there’s no real technical tolerance for mistakes. For example:

  • Connecting a microphone to a line-level input will result in almost no sound at all, because the mic-level signal is too weak to drive the line-level input
  • Connecting a line-level source to a mic-level input will cause the sound to be loud and distorted because the line-level signal is much stronger than what the mic input will accept. (Note: Inputs and outputs on some higher-end mixers are mic and line level switchable.)

Helpful Hints

  • miclevel input is typically a female XLR connector. A linelevel input is typically an RCA jack, 1/4″ phone jack, or 3.5 mm phone jack.
  • Don’t assume that the levels match just because one connector fits properly with another. Inputs are generally very clearly marked.
  • If there is only a mic input on a device (for example, a digital recorder or a computer) and you need to connect a line level device to it, you can reduce the voltage by using an attenuator or a DI (Direct Injection) box, available at most music stores. There are even cable versions with built-in resistors that accomplish the same task.
  • Different wireless receivers have different output levels. This is true for the Shure line of products and with most competitor brands. Consult the user guide of each wireless receiver to determine its output signal level. Mic level can vary as much as 20 dB between different receivers.

 

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Justin Boller

Justin Boller

Justin Boller is an Applications Engineer at Shure Incorporated by day, assisting customers with product selection, system design, and troubleshooting. By night he is a professional musician, performing on tuba, electric and acoustic bass, guitar, trombone, and other instruments in various musical ensembles. He holds a B.S. in Music and an M.S. in Arts Technology from Illinois State University. When there's any spare time, he also enjoys tinkering with electronics, cycling, and cooking on the grill.

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9 Comments

  • can ozen says:

    I work on an e-commerce site that sells a Shure headphones and Shure microphones (www.infomusicshop.com/shure). Our customers were constantly asking questions about this content. I really like the article about this subject. Thank you very much

  • Duncan Gray says:

    One very minor correction and one bit of additional info:
    40 dB (regardless of being dBu or dBV) is a ratio of 100 in voltage and 10,000 in power. 60 dB is 1,000:1 and 1,000,000:1 respectively. The nominals that Justin quoted are correct, but the span in differences is even more impressive than the 1,000:1 that he listed. Think of it … 1 million times weaker …

    Second, the dBu is a historical normalized voltage agreed on in the 50’s. It is 1 milliwatt into 600 Ohms. This is sqrt(600/1000) ~ 0.775. They are not far apart from each other, 0 dBu is just 2.22 dB weaker than 0 dBV. No real good reason for the difference, but these are the conventions used.

    Thanks for the great refresher, Justin. I agree with @Anonymous. Shure is always a great choice.

  • nicholas rose says:

    There are two standard line levels:

    -10 dBV for consumer equipment (like MP3 and DVD players)
    +4 dBu for professional equipment (mixing desks and signal processing gear)

    Well, yes. But are these typical levels, average levels or peak levels ? This is rarely stated, but important. And why mix dBV and dBu ?

    • Justin Boller says:

      Hi, Nicholas!

      0 dBV represents a 1-volt RMS (Root Means Square) signal; 0 dBu represents a .775-volt RMS signal.

      Consider this an “average” line level signal, as many mixer inputs have an actual clipping level as high as +24 dBu to provide headroom for audio peaks.
       
      Specifying “consumer” line-level in dBV and “professional” line-level in dBu is an industry standard. The Yamaha Sound Reinforcement Handbook is an excellent reference book that contains more information about their origins. With modern audio equipment, the difference really is not significant.

      Hope this answers your questions!

  • John Kaczmar says:

    Hey man, I liked your article. I’m a live sound engineer in Brussels (originally from the U.S.) Thanks for the refresher!
    You learn these things in school and guys like me can forget.

  • Anonymous says:

    As always I find Sure Quality not only in products, but your people too.

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