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.

Disclosure: If you buy through this Amazon USA link Geoff receives a small commission from each sale.
European and Australian readers can use the links on the side panel - Thanks for the support

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PHOEBE YI (Rancho Cucamonga)

I have a DAC with a RCA output and a aux output. When I connect my earbuds to these two, the output volume are very different. The RCA offers very low volume. Can you pls tell me why and how to solve this issue?

3006 (Corpus Christi Tx)

Thanks for the great article — but it doesn’t appear to apply to my install. I have 1/4 jack aux outputs on my PreSonus StudioLive 16.0.2 mixer. I want to feed one output into my Sony camcorder 1/8 mic input, and the other output into my IP camera for live video/audio streaming.
When I plug in the Sony camera has no audio
When I pug in the IP camera I have to increase the gain inside the camera software and I get very low volume and distorted.

Please advise.!

PB (USA)

Hi Geoff, I have a question about relatively high line level output, as in 8 volts. As an example of this, I have a car stereo head unit capable of 8 volts at line level. This is a competition type deck designed for external amps and to optimize their overall performance. My question has to do with line level limitations for other small amplifiers like those that would normally expect to see around a volt or so. Would 8 volts of line level damage these smaller amplifiers? I would like to re-purpose this car stereo head unit for a portable… Read more »

David (San Francisco)

Hi Geoff, Good information. Thanks for clarifying. I have a couple questions. First, the service manual for my car says the radio and audio amplifier have a DC bias voltage that is about 1/2 the battery voltage. The audio is produced by varying AC centered around the DC bias voltage. Is this normal for car stereos? Can I just change the speakers with aftermarket brands, or do I need special speakers for this? Second, the radio in my car only has 4 speaker outputs, but the amplifier has 9 outputs. I found out that they used the same radio on… Read more »

Ctaya (Canada)

Hi Geoff,

If I connect the headphone output to a line input of my amplifier, the sound is quite weak. Can I connect it to the phono input of the amplifier instead?

Alix (Austria)

Sir,I’m very greatfull for this article…
You have helped me a lot explaining the levels and resolving the problems.
I have a keyboard and camera mic input,and I had no clue what to do,and now You’ve saved me my friend.

Thank You a lot for Your time writting this article,and thank You to share this information with us.

Wish You all the best in the future my friend!

Sandy (BC, Canada)

hello, I loved this article. it is very informative; I have a project I am working on and I have been scouring the internet all day and night trying to research possible problems I might encounter. I have a late 40’s Wurlitzer jukebox that is missing the amp and record guts. I plan on hooking up a car cd receiver and running the line out, or as it states in the description: 2 Pre-Output Terminals (Front + Rear / Subwoofer Selectable)4.8v Line and Subwoofer Pre-Output LevelMOS-FET 50W x 4 (20W RMS x 4) , I will be running this into… Read more »

Phil Wilson (Corolla, NC.)

Your information is great but I hope you can assist me I finding,maybe making a device that I or anyone can add to TV’s that allows the viewer to adjust background sound/music ETC. in programming. Example I am watching a action show and the background music is louder than the actors speaking thus my ability to clearly understand the full conversation is hindered. I have found this increasing since transmissions became digital. My thought is that I am sure there are many others that must have these same issues. So it seems like a device that is put inline with… Read more »

Wawan (Indonesia)

Hi Geoff,

I’m Wawan from Indonesia. I’m a newbie in this audio video stuff.
I have radio with no ‘line out’ jack. it just have built in speaker and headphone jack.

I have an amplifier. it has ‘line in’ socket.
I want to connect from radio to amplifier. how can I do it.

is it ok to direct connect from headphone socket to line in of amp?
or I need some stuff ( maybe DI box ) before connect.
ie : headphone jack –> DI box –> line in ?

terima kasih / thank you ^^

Jeff (Sunnyvale, CA)

Geoff (or anyone): I am looking for Audio Electronics instructors in my area. Anyone available?