What are VU meters and why should I use them?

VU meters are a measurement tool that shows the average level of an audio signal.  

You need VU meters for two big reasons.  One, they hear loudness the same way our ears do, and two,  they force you to put headroom in your mix.  

Headroom is so important it will take another whole article to tell you why you need it.  Just trust me on this one, you NEED headroom.

Now, VU means "Volume Units" and it was standardized in 1942 to use with telephone and radio broadcast equipment.  

I'm sure you already know their warm glowing faces from all sorts of analog gear, and in the movies, and all over the place where people want to show a picture that says "music in action".

In digital audio it's more common to see Peak meters, which only measure the top volume spikes.  That's great for preventing digital distortion, but it is not how our ears actually hear loudness.  We don't react well to peak volume spikes because Ouch!  

Peaks make us flinch.

Our ears hear loudness by feeling the average sound level over time, and this is what VU meters show you.  

By the way, "average level" is often referred to as RMS. You'll see that on the Ableton compressors and lots of other places.

RMS means "Root-Mean-Square".  It was originally a mathematical average taken from the square root of the signal voltage over time.  Don't worry about the circuit math.  RMS means average, Peak means Peak and you need them both.

Why do you need them both?  Because they do two different things.

Peak meters tell you how to avoid digital distortion.  This is really important because digital audio has a hard limit and beyond that you get a particularly awful type of distortion.  

Peak meters are simple to use, just keep the meter in the green and bring down the volume if it turns red.  You already get this concept, it's obvious like a stop sign.

VU meters (RMS) show you how loud a sound feels in real life.  You need them to compare how much space a sound takes in the mix.  

Use RMS, or VU meters, to compare two sounds to each other and get a realistic picture of how loud they are.  (A peak meter doesn't do this very well.)  

For example 
If you have a bassline that peaks at -5dB, and a drum loop that also peaks at -5dB, it does not mean they will sound balanced next to each other.  They probably won't.  Drums are a sound that peaks with very short, loud transient spikes far higher than the actual loudness of the whole kit -- but a bassline has low, fat transients that peak very close to its average level.  

End result, a bassline will sound way louder than drums when you measure them with a Peak meter.  But if you set both your bassline and drum loop to -5db using RMS/ VU meters, they will sound balanced to the ear.  

VU meters react more slowly, like our ears, which gives you a realistic picture of the loudness that a sound is pushing.  You can't really use Peak meters to compare the loudness of two sounds as they appear to our sense of hearing.  And music has to appeal to the ear, right?

Right.  So why do I need a plugin for this?

You need a VU meter plugin because the Ableton meters don't show RMS / VU level very clearly.  

In Live, the light-green bars on top show Peak, and the dark green bars in the middle show RMS.  I love it that Ableton added this function, but it's still  not easy to read numbers for the average level.  

If you want to see the numbers, you need to expand the tracks horizontally... but in a big session that can take up too much space.  

Ableton fact:  Each line on the side of the track volume shows -6dB 

These lines are useful when the channels are minimized for horizontal space, but it's still kind of hard to see what the RMS level is doing.  Sometimes I want to see a more precise and larger meter.

That's why I like this plugin from TB Proaudio.  It gives you a big fat screen that you can park anywhere you want, and a needle that you can see without counting little lines.  In fact I like to keep this VU meter in my peripheral vision and work without looking directly at it.  A little like the tachometer when you're driving stick shift.

Here's the link to download it free.
http://www.tb-software.com/TBProAudio/mvmeter.html

HOW TO USE IT
Download the PDF manual along with the plugin.  Set the meter to VU when it first opens.  Click the word "Peak in the center to see the options for VU and other standards of reference.

When you first try to use VU mode on the master channel, the meter will probably be spiked in the red.   That red light labelled "OL" means OverLoad and it's telling you that your master channel is already way too loud.

But don't touch the master volume fader!  You will not get anywhere by trying to lower your master volume.  

The right way to use a VU meter is to leave your master volume at 0, and lower all the other channels in your session until the meter is bouncing near 0.

This will put your average mix level around -18db, and now we have arrived at the real reason you should be using VU meters.

VU METERS HELP YOU KEEP THE HEADROOM IN YOUR MIX!

THIS is exactly what VU meters do to save your mix from four or five other disastrous problems all at once.

To get the VU meter working right, your master channel RMS level needs to be somewhere around -18dB.    This automatically makes you mix a lot lower, keeping a lot more headroom, and avoiding that flat, lifeless, dead digital sound that people complain about.

HEADROOM.  If you want to understand headroom, just think of a house party where people start dancing.  What happens to the furniture?  It has to get moved out into the other room, upstairs, into the hallway or even outside.  You can't have people dancing in a room full of chairs and you can't have loud, clear music in a mix with no headroom.  

We'll leave that topic here until the next article which will go into more detail on exactly what disasters come from losing headroom.

And now you know why mixdown is called "mixdown".  You actually mix the channels DOWN, and make space for your mix to breathe.

ANNOYING QUESTION
Why do we need to mix down in the first place?  Can we just start with quieter sounds?

Answer: No.  For the best quality of sound you have to record your sounds coming in at the highest level possible.  This is called a good signal-to-noise ratio.

The sound you want is called the signal, and the noise in the system is called noise.  Sources of noise are things like background noise, static on the cables, fuzz from a pre-amp turned up loud, and the combination of them all together.  It can really degrade your music.  Think of tape hiss.

That is just to say, there is a very good reason for recording too loud and then mixing down later.  

It's how you get the best music in the end.

LEARN TO MIX

Finally, if you’d like some help to learn how to make tight, solid mixes for electronic music, check out this revolutionary hands-on Ableton Live mix course.