Understanding Audio Levels

A basic understanding of the general audio levels mentioned in this article will help you avoid the common mistakes often made when connecting audio devices together. We are going to talk about three different general levels of audio signals.  The names of the three general audio levels are speaker level, line level and microphone level. For simplicity, the different audio levels are described in volts. For an understanding of decibel levels used in audio, see the articles on decibels starting here.

Speaker Level

A speaker needs a few volts of electrical audio signal to make enough movement in the speaker to create a sound wave that we can hear. Small speakers need only a few volts, but large speakers need 50-100 volts to make a loud sound.

Line Level

A speaker is connected to an amplifier. Think of your HiFi amplifier at home. What plugs into your amplifier? DVD player, CD player, radio/tuner, video camera. All these devices plug into the “line in” or “Aux in” of your amplifier.  “Line IN”, “Aux IN” and “Line OUT” all have an electrical audio signal at line level. You are probably aware of the standard red and white leads used in HiFi equipment, these all use line level. Other plugs are also used for line level. Line level is about half a volt to one (½ – 1) volt. It is the job of the amplifier to amplify the half to one volt of line level, up to the 10 volts or more of speaker level.

Note: A common error is to connect plugs and sockets together just because they fit. Don’t assume audio level based just on the type of plug being used. The same type of  plug can be used for different purposes (and different audio levels).

Microphone Level

Ok , so we have line level (about ½ – 1 volt) which goes into an amplifier to make it up to speaker level (about 10 volts or above).  What audio level do you think Mic level is? How much voltage do you think comes out of a microphone, as a result of you speaking into it? Answer: Stuff all!

The output voltage of a microphone is very low. It is measured in milli-volts, that is 1/1000th of a volt. A mic can give as little as 1 mV, or upto 100 mV, depending on how loud you speak into it. That is not very much. So what do you think is going to happen if you plug a mic directly into the line in of an amplifier? Answer: A very low level of muffled sound if anything.

Mic Pre-amps

The amplifier is wanting line level, ½ – 1 volt to produce enough signal to make the speaker work properly. But the mic is only producing milli-volts. So what is needed is a small microphone amplifier that amplifies the audio level from mic level to line level. This should go between the microphone and the amplifier. Because it is for the microphone and it is before the main amp, it is called a mic pre-amp. A mic pre-amp amplifies the milli-volts from a microphone up to line level.

Mic pre-amps are normally built into devices designed for connecting to a microphone. Equipment like an audio mixer, a digital recorder, a video camera or a computer – all these may have mic level inputs as well as line level input, or just a mic level input. .

Audio level microphone level, line levelThe picture on the right shows for each input on this mixer there is a line level input (labelled Line 3 and Line 4), as well as a microphone pre-amp (labelled MIC PRE).

Obviously a microphone plugs into the mic input, as the mic inputs are connected to the in-built mic pre-amps.

A line level device would obviously plug into the line in socket.

But what if your mixer (or camera/recorder) only has a microphone input, and you need to connect a line level source to it? This would result in the line level (½ – 1 volt) being connected to the input of the mic pre-amp. The trouble is, the mic preamp is expecting only a few milli-volts. The resulting sound will be very distorted as the mic pre-amp is completely overloaded.

Attenuators

So how can we do this? How do we connect a line level to a mic level input? We have to reduce the line level down to mic level.  The technical word for this is to attenuate the signal. As an amplifier amplifies, or boosts the signal; an attenuator attenuates, or reduces the signal.

You can buy attenuators at a music shop, they are called DI boxes. DI stands for Direct Injection, meaning you can directly inject a line level into the mic input without any problems. It is also possible to make an attenuator, possibly with variable attenuation, to cope with different levels. It is also possible to buy or build a fixed attenuator in a cable. This is a cable with resistors built-in to the plugs to attenuate the line level down to mic level – this is very useful for a video camera or portable digital recorder.

Audio Level Summary

There are three main audio signal levels: mic level (millivolts), line level (around 1 volt) and speaker level (around 10 volts or more). The rule is, only plug speakers into the speaker socket of an amplifier; only line level into the line in of any equipment; and only mic level in the mic input of your mixer, camera or laptop.  The most common cause of  audio distortion comes from not understanding the different levels, and how to connect them all together.

Practical Example 1

Scenario: A keyboard (electric piano) located on the stage needs to connect to a mixer located at the back of the hall, with a microphone multi-core cable connecting between the two.

Issue: The output of the keyboard is at line level, and the microphone input at the mixer requires mic level. (There is also the issue of different plugs and balanced/unbalanced inputs but these are the topics of other articles).

Solution: Use a basic DI box available from most music or electronic stores. A DI box acts as an attenuator which reduces the line level of the keyboard to mic level for direct connection to the mixer (via the multi-core cable). The DI box also overcomes the issues of matching plugs and going from unbalanced to balanced  – so this is a perfect solution. This solution also works for connecting electric guitars, electronic drums and DVD players.

Practical Example 2

Scenario: The output (line level) of an audio mixer needs to connect to a digital camera or digital recorder which only has a microphone input.

Issue: The output of the mixer is at line level, and the microphone input of the camera/recorder requires mic level.

Solution: A basic DI box could be used, but this would require an input lead, and output lead and the DI box  – a lot to carry in your camera bag. A neater solution is to have a lead with a 40dB attenuator built into it. This will reduce the line level from the mixer by a factor of 100, which will bring the line level down to a reasonable mic level to connect directly to the microphone socket of the camera/recorder.

This article is based on one I originally wrote for my friends at CamcorderUser.net, and has been refined by their helpful comments.

Please Note: During the Covid-19 pandemic I'm busy with a number of streaming projects, and have very limited time to attend to this website. I'm currently taking up to a week to answer questions. Sorry for any inconvenience.

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European and Australian readers can use the links on the side panel - Thanks for the support

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Chris

Very informative and easy to understand! Thank you very much, Geoff. I have been searching for a solution to my problem that I have been facing, and I think I may have found it here. I have been attempting to plug a digital mp3 playing device into my stereo receiver via its “CD in” port by using an RCA to 3.5 mm jack. The receiver is an Onkyo tx860, and it is attached to two 4 ohm NAD towers. At first I thought that the mp3 player was causing clipping in the speakers, even at barely audible levels. I found,… Read more »

Mike (USA)

Hi Geoff. Great article. I’m coming from the video world but audio plays a big role. Please bear with me. I record live performances on stage and take a direct line feed out from the mixer (which I assume that’s all there is) and it’s always hit or miss in getting a decent level ie: too soft or over modulated. My video camera does have the ability to accept Line, Mic or Mic +48v. The camera audio reference level set to -20db. I also have the option to adjust the MIC input reference level to -62db,-56,-50,-44,-33. I also have an… Read more »

Baz Jones (Ryde, Isle of Wight)

Hi Geoff, I have just recently discovered my old Sony turntable in the loft. I have a BOSE CD/Radio (The smaller one). Recently I bought a Two Phono to 3.5mm Stereo Adapter from Maplin and linked it up to the Aux socket in the BOSE. The result? Very ,very faint sound . I also have a portable CD player which also uses a 3.5 mm stero plug and this works perfectly. Why won’t my old LP’s play?

Gurdeep (India)

Hi sir,
I need help. My lg tv had no 3.5 mm headphone jack. So i purchased dual rca male to 3.5 mm female jack from amazon. But when I plug in my headphone to tv via this cable the sound out is extremely low. I connected 5.1 speakers and they work fine with full audio. But while connecting headphone sound is too low and cant increase as well from tv remote. Please help me as i need full sound from headphones. What else i need to connect to my tv?

Gareth (London, UK)

Hi Geoff. Thanks for giving voltage ranges of the levels – that’s what I was particularly after. I’ve got an unusual situation involving a phone being used to page (announcements) and connecting it to a public address system. I’ve hijacked the speaker output of the phone – which is a small, mono 4 ohm 1W affair – and at mid volume level it will directly connect to a cheap line level input ipod speaker. Trouble is that it has to go into a mic input on the PA. I’ve ordered a car speaker to line level convertor for when I… Read more »

Karthik (Boston USA)

Hello Geof, The website is informative. Thanks. Recently I picked up a Panasonic 5.1 AV reciever. I was not happy with the front left and right satellite speakers. So I got a used Panasonic stereo CD changer system which has a pair of 3 way speakers(Panasonc CD changer + Left 3 way speakers + Right 3 way speaker). Unfortunately, the crossover circuit for the 3 way speakers are inside the CD changer centre console instead of inside the speakers. So if I decide to use the speakers, I have to send the audio through the center console which has a… Read more »

Jacques van Rensburg (Cape Town, South Africa)

Hi Geoff I’m grateful indeed for the illuminating article and all your time spent replying to people, much appreciated. I have a question too, if I may… On most cheap domestic IA’s like the Cambridge Audio Topaz AM5, one’s likely to find a set of ‘rec out’ sockets, but seldom ‘line out’ or ‘sub/pre’ sockets. I understand these are all vastly different levels, and I’m looking to connect a ‘line in’-only active subwoofer (no high-level speaker in/through) to said amplifier. I would like to know what sort of device (an attenuator/resistor perhaps) I’d need in-between the two components, in order… Read more »

Pat (France)

Hi Geoff,
I would like to connect the output of my Fishman Platinum Pro Eq bass preamp (used with a piezo pickup on my double bass) to a Bose Soundlink iii speaker.
Can I connect the 1/4″ amp output of the preamp to the 1/8″ aux input of the Bose speaker ?
Can I connect the XLR D.I. output of the preamp to the 1/8″ aux input of the Bose speaker ?
Is any of the 2 above scheme preferable ?
What kind of cable should I use?
Many thanks in advance for your advises.
Regards,
Pat

Rick (BC, Canada)

Hi Geoff I need to take a better look at your website when I have the time – right now I’m frantically catching up with spring yard cleanup and maintenance. One quick question for you. I’ve just retired from the military and living out of a duffel bag for a bunch of years. Dusted off my old Harmon Kardon stereo system to once again have quality sound now that I have a permanent residence again. Of course, the audio scene has changed just a tiny bit during the intervening years, and there are new audio toys out there. So, quick… Read more »

Brent Baldwin (Nicholasville, Ky)

Can I ask a question not sure how this works but in reading this article I think I know the answer but I want to know if I am putting my stereo at risk. I have a factory radio that has an input for a video dvd aftermarket player installed in the roof it has an option for an additional line in(rca)with red and white as well as a video (yellow) line level inputs. My son got a cable that converts the earphones out of his iphone to the rca inputs on the dvd player so he can play music… Read more »