The science and art of metering
Why we all need (calibrated) VU meters
So you’ve sorted out your room, auditioned your monitors, carefully chosen all the gear, what are you going to do about metering?
Although you get a set of free meters in your DAW, you will need to purchase some more, and if you have any analogue kit, you’ll also need an analogue average meter, like a VU. This article will go through the whys and what’s of metering, so at the end you’ll hopefully know what to meter and how to meter it.
We’ve researched this article by speaking to some of our many clients, and reading lots of literature. This is a long read, so if you’re impatient, you can skip the science bit and go straight to the results, by clicking here.
Do you actually need a meter?
It is possible to work without meters, just as it’s possible to do all audio edits with a razor and tape, it’s just not very practical. These are the main reasons why you need audio meters:
- Streaming services will alter your masters to suit there needs if your work doesn’t measure right
- To tell you if you’ve clipped the signal slightly ( you often can’t tell with a casual listen)
- To give you feedback on the current levels
- If you need to calibrate anything in the analogue domain ( converter levels etc)
- If you need to fault find anything in the signal chain (cable problems etc)
- To accurately compare relative levels of signals (A/B testing)
As you can see, there’s quite a few reasons. We’re going to concentrate on points 1 to 3 in this article. Here the meters fall into two main categories: producing an absolute metric to measure what you are doing against a standard, or providing a sense, a feedback of what’s happening as you work.
Nearly every thing has an absolute maximum, above which it can’t function. With analogue, this maximum varies with the electronics ( unbalanced gear is about +22dBu, balanced, +28dBu), or the storage medium ( tape & vinyl have different variables). However once you approach or reach the maximum level, your output is soft to hard limited, (clipped). When we lived in an analogue world, there were broad standards or local studio standards, but because of the variation there was no absolute maximum standard.
Digital by contrast is very well defined. The maximum level is 0dBFs. It doesn’t matter what device or process, that’s it. Any unlike analogue, because digital clipping is very hard ( not clipping at -0.01dBFs, full clipping at 0dBFs) it is very useful (or necessary, see streaming section below) to know what you maximum level is. This is the job of a peak meter.
Peak meters are very fast and read the absolute level of the signal, so they help you know if you’ve clipped the signal digitally. Often they have sticky readings, so you will know the highest level reached, and also the number of samples that you have clipped. Some meters can estimate by how much your track will be clipped in the future (true peak meters) when your track is processed further by codecs or DACs.
Do what? – let me explain: The chances are that apart from cutting to CDs, your lovely PCM files will be processed further by a codec ( MP3, AAC etc) and depending on the type of codec, it will need a bit of headroom in the signal when it does the maths, and a signal that rises fast, but hits the 0dBFs maximum can cause problems for these codecs, resulting in a less than optimal conversion. The same thing can happen with consumer oversampling DACs (and that’s virtually every DAC out there). True Peak meters work out what the peak would have been if it didn’t get clipped at 0dBFs, and this true peak level is what you need to worry about.
There are analogue versions of peak meters, PPMs which were a mainstay of broadcasters, but are less used today. The True peak meters are pure digital machines, and they should be used inside the DAW. You can buy them as a plugin.
These are a new type of meter and use an industry standard algorithm to measure your work against an absolute loudness standard ( ITU-R BS:1770-2) . They produce a set of loudness metrics, expressed in LUFS (Loudness Units relative to Full Scale). These figures are important because unlike a CD, streaming providers normalise, clip or limit songs based on these loudness metrics. Only by knowing them can you be sure that a streamed track has a chance of sounding the same as the un-streamed version you’ve mastered. A loudness meter will come with a true peak meter setting, as both absolute readings are needed to quantify your work.
Sense/ feedback measurements
These measurements tell you where you are now, rather than providing a set of metrics for the whole piece of music you’re working on. Generally these sort of meters are much slower than peak meters, and show the average level (loudness) of the track over the last third of a second or so. For that reason they’re really good at giving you a feel for the overall loudness of a track, where it’s going and where it’s been. RMS meters and proper VU meters are this type of meter.
The real key to these sort of meters is that once you calibrate them, you can glance at them to get a rapid idea of where you are, without taking your focus away from the music you’re working on. Other types of meters provide so much moving information that you are distracted by them ( especially if they are sitting in your eyeline on your main DAW screen), and your brain switches focus from your ears to your eyes. You can easily test this for yourself – your brain does not cope with simultaneous stimulus very well.
Ideally you just need to glance at these meters occasionally to give you feedback that you’re on track, rather than stare at them constantly. Although more expensive than software meters, this is an advantage for hardware meters (real bits of kit) over software meters that run in windows on your DAW. There are also different ways of displaying the level, some with mechanical meters, like an original VU, and others with LED bars or displays like PPM or Jellyfish meters. They also don’t take up valuable DAW window space.
What medium is your work going out on?
Today, your work is going to end up on one of these mediums:
- Streaming (includes broadcast and YouTube etc)
Each one has specific level requirements. Lets have a look at each one, but I’m going to concentrate on streaming, as it is the most demanding, and important.
Ever since it was pronounced dead, it’s gone on to do very well. Cutting to Vinyl is an art, and a lot of experience is needed to make a good cut. The levels can alter depending on a whole range of variables including the spectrum and length of the music and where it sits on the track order. Generally, levels are matched using a VU meter to show average levels with a RDL unit to adjust the actual cutting level. The material to be cut needs to be quite heavily processed to be suitable for a lathe. Although not as extreme, recording to analogue tape follows a similar route, and VUs are often used to represent the average level put on tape.
Ah 1982 the CD arrived and nothing would ever be the same! I actually worked on one of the first UK produced CD players, when I was at Meridian, but that’s another story 🙂
CD’s became the source of our loudness wars – with no level standards like vinyl before it, the average level on CDs could be whatever you fancied. Initally it followed sensible standards, with good dynamics, and the peak under 0dBFS. Then some oik figured out that people respond to louder songs ( I don’t even think this was scientifically validated re sales), and sheep like, we all followed suit. A consequence of this was that the dynamic range was reduced, so that the average level was often a few dB below 0dBFs. In recording, a calibrated VU could work perfectly with reduced dynamics to show you how much headroom you had. A peak meter was essential to see if you’ve gone over 0dBFs, but often we generated loudness by clipping the ADC in an analogue transfer path, so the peak meter spent most of it’s time at maximum.
Today you can still cut a CD as loud as you like, and a calibrated VU will do the job of showing you how close you are to the limit, just fine. However if your work will be MP3’d or sent to a streaming service, unless you want to make separate masters, you’d better take note of the settings for streaming, below. There is no reason not to use these settings on your CD, and arguably it will sound better for it.
As a side note, the CD is still the perfect delivery mechanism for classical music. This is simply because you can define your levels, average and peak to suit the piece of music in front of you. You also know the original dynamics of the music and you know your audience, and what they will expect. And you never got involved with loudness wars anyway.
It’s the future apparently. Because on a stream, people listen to music sequentially (including broadcasts), the loudness wars messed things up, and people would constantly be turning up or down the volume, especially with broadcast adverts. Initially the streamers responded with super program level conditioners that normalised the inputs, but slowly they have all adopted the loudness standards. This is how they process your music.
- They by default engage music normalisation for all their users
- They scan your music file and work out the true peak level and the integrated loudness LUFS metrics
- They either raise or lower the replay level so your LUFS matches their reference playback LUFS
- They clip or limit your maximum level so that after adjusting the volume of your music, it does not exceed -1dBFs
There are slightly different rules for Album normalisation. The current view is that you should normalise the loudest tracks on the album to the reference, but then keep the levels relative for the quieter songs. This means working to a lower LUFS figure to these songs.
What are the magic references?
There is an AES standard for all this. It’s a quick read. It states that the maximum true peak level should be less than -1dBFs, and that the integrated LUFS should be between -20 and -16LUFS. The various streaming services of course all have their own standards, but they are all pretty similar: true peak level is less than -1dB, and maximum integrated LUFS is -13 (YouTube) to -16 (Apple).
In practice, this means that if you exceed -13 LUFS, your work may simply be turned down a bit, at least it won’t be compressed or limited. Of more concern is if your LUFS is too low but the music is very dynamic, like a classical orchestral piece for example. Here the average level would be raised up, and the peaks could be compressed or limited. I’ll do some more research on this subject and let you know what I find in a separate article.
How to meter for streaming
You will need your loudness and true peak meter to know what is happening, but if you’re working on normal music, you can just let these metrics run, and instead glance over at a calibrated VU meter to see if you’re running into problems. How so?
You are employed as an experienced human, not a machine, so you should be mastering with your ears, not with your eyes. Your primary job is to ensure that the emotion of the music in front of you is preserved or enhanced and transferred to the listener, not that it’s integrated LUFS is -13.65dB ( for example).
It’s down to you, using your skills and experience to get the best out of the track, but nearly everything you do (EQ, compression, limiting levelling etc) will alter the integrated LUFS level. If you keep looking at the loudness metrics, you will go quite mad and most likely make bad musical choices. Now lucky for you, most natural music has a peak to average level of about 10-12dB, and although this can vary across a track, if the average level stays below – 10 dbFs or so, you know you’ll be OK. So to save yourself grief, set up your VU, so that 0VU is about -13 to -14dBFs, then when you’re adjusting the music, just glance over at the VU’s to make sure they aren’t going into the red too much, or pegging.
In this way you can just adjust the loudness or dynamics to make the music work for your ears, and just keep an eye on what the VU meters are doing for feedback. At the end of the process, you’ll get your loudness metrics and you can decide if you need to make any overall level or compression changes.
While you’re doing this, make sure you keep your master volume control constant through the main process, so you hear what the user will hear. Sure you can adjust it to listen to detail or fade outs, but return it to your reference listening level afterwards. Remember that if you let the overall volume in your room rise, it may sound great, but when it’s levelled back to -14 LUFS on Spotify, it will sound tonally quite different.
So in summary, what meters do you need
A true peak meter
You need to know your peak level. Even if you choose to clip music for artistic effect, you can’t dictate what upstream codecs will do to your track. In addition because of the way that oversampling DACs work you need a “True” peak meter. This analyses where the music was going before it got clipped or limited, and the result can be as much as 4dB higher than you thought! The AES recommendation is that the maximum level you output should be -1dBFs (True Peak) to leave 1dB of headroom for lossy encoders to do the maths on your tracks correctly.
A loudness meter
You need to know your loudness metrics for streaming releases. Specifically you need the integrated loudness figure in LUFS to know how to change the level of your track to stop the streaming service from messing with it.
Often you’ll get a plug in that has a true peak meter and a loudness meter in one plug in. The peak and loudness meters analyse the track over the duration of the track from start to finish and provide you with metrics at the end to specify the “streaming friendliness” of your track. However they are mostly irrelevant while the track is playing – their indisputed value is at the end of the track.
An analogue calibrated VU meter
At first sight, if you’ve got the combined loudness meter, you don’t need a VU meter. The loudness meter is super high tech, lots of graphs, numbers and lights. But let me give you an analogy: When mobile phones first came out, loads of Millennials, ditched their wrist watches and embraced the new tech; if they needed to know the time, they could just look at their phone. But as time passed, they started wearing their watches again. Why? Because they realised that they didn’t want to find and open their phone to find out its 19:48:32, they just wanted to quickly glance at their watch to see it’s about 10 to 8.
A proper analogue VU works the same way. When it’s properly setup, you can just glance at it to work out if you’re running too hot or not. You don’t need to stare or interpret numbers, a glance is sufficient. This keeps you focused on working with the music with your ears, not worrying about numbers with your eyes.
The calibrated bit above, refers to making sure that the VU is adjusted so it reads properly with the levels you’re working with. Our meter attenuators built into our VUs let you do this easily.
How to use it all
So now we’ve got our loudness/true peak meter and a VU meter – how do we use it?
Connecting up the meters
The loudness/peak meter needs to monitor your final output. As a plug in, it’s easy to place at the end of the process in the DAW. As hardware, you’ll need to connect it digitally to the DAW and tap a digital send accordingly. You can’t do this with an analogue connection.
The best place to connect a VU meter is to your monitor controller meter output. This lets you meter what you’re listening to, before the volume control. If you’ve got a decent monitor controller, you’ll be able to look at levels pre and post the record path, so you can see how the relative levels are changing (A/B checking). If you can’t access this on your monitor controller, you can connect it to a spare analogue output on the DAW, and feed this with a copy of the signal you’re monitoring. VU meters have diodes in them and if not buffered can alter the sound slightly, so don’t connect it directly to the analogue signal you’re monitoring without a buffer.
To make sense of stuff you need to work to a calibrated level. This means that you know what your normal monitor volume is, and you’ve adjusted your VU attenuator so this level hovers around the -2VU marking (why? see below). Then any changes you hear louder or softer, or higher or lower on the VU scale helps you instantly judge what you’ve got to do.
Remember the whole point of the volume normalisation of the streaming services is to make sure that the listener shouldn’t have to turn their music up or down as the tracks change. Nor should you have to when mastering.
The process is not involved, but I’ll detail the exact and preferred method in another post. For now, you want to play a piece of pink noise that meets the streaming metrics ( -14 LUFS) and establish a comfortable reference volume level on your monitors. Then you need to adjust the attenuator on your VU meter to centre around the -2VU to -3VU mark for most of the track. This means that when the VU is reading its maximum ( +3VU) the average level is about -9 LUFSs, leaving you 9dB of peak headroom. You can adjust this calibration slightly over time as you get more experienced with LUFS, but you’ll soon get used to instantly hearing if you’ve got to turn the monitors up or down for a new track, and if the VU levels are peaking or dropping.
You’ve got to play out the entire raw track before you work on it from start to finish to get the raw loudness metrics of what’s been supplied to you. I’m sure some file readers will just do this for you, but you might as well take the opportunity to get a feel for the song and what you might like to do to it.
When the song finishes you’ll know what the maximum peak level is and what the integrated loudness also is. You’ll also get a feel for how much you altered your reference volume when listening to it. From here, you’ll have a good idea what you can do with the overall levels and dynamics in the track.
The VU meter is not perfect, but then neither is your ears, room or speakers. However like those great instruments, after a while you get used to their imperfections and compensate accordingly. A mechanical VU then forms part of your operating system, proven and reliable letting you focus on the sound using your ears, and not get overwhelmed by metrics, graphs and digital readouts. Plus VUs look really cool too!