It is, however, no accident that at least a pair of VU meters still grace the most revered mixing consoles, tape machines and compressors on offer. (Not to mention every mastering room worth its salt.) The most seasoned of engineers and producers will often be seen eyes fervently drawn to the needles. Relayed in those glimpses is the invaluable information of just how much energy and loudness is contained across the gain structure and truly where the level of your mix is actually sitting.
So what exactly is a VU meter? To operate a sound recording and reproduction system, some method for determining signal levels to avoid overloading, noise and distortion is required. This is the purpose of the VU meter. A VU meter is used to measure power levels of audio frequency signals. Such meters employ special ballistics that average out complex waveforms to properly indicate program material that varies simultaneously in both amplitude and frequency. For complex waveforms such as speech, a VU meter reads between the average and the peak values of a complex wave.
VU meters are designed to have a dynamic characteristic that approximates the response of the human ear. When a speech waveform is applied to a VU meter, the movement will indicate peaks and valleys in the signal. A peak program meter (PPM) by contrast indicates not average levels but these peaks with incredibly quick response. The VU spec itself is well defined, and tells you what the rise and fall times of the meter should be. It's these times that are difficult to get right, but are so essential to getting a meter that properly reflects music loudness, rather than just bouncing up and down to the music.
The important consideration is that there is only so much level that will go onto a finished CD, data file or piece of vinyl before overloading and distortion. VU meters show you much more accurately where that level is and, thus, your limitations.
Historically most master mixes were committed to 1/4" or 1/2" analogue tape. In this period you were restricted to the level you could get on said medium. For 1/4" and 1/2" tape, this was around +3 VU. It increased later with higher output tape. As the majority of recordings during this time were also mixed on analogue consoles, you were restricted by the level at which you could output from the mix bus before overloading and distortion. Even on today's latest analogue mixing consoles you face this restriction. Perhaps the maximum level you can work to is around +5 - 6 VU. Working solely in a digital audio workstation, or "in the box" as it's often referred to, you can output at higher levels.
The generally recognized maximum level achievable on vinyl is around +6 - 7 VU. On a digital format, though, it's now pushing upwards to around +10 VU, though most modern releases sit at around +8 VU. In order to achieve these higher levels, you start to implement dynamic limiting—for better or worse.
but you have to know where that loud is."
My crusade for wider use of VU meters stems from the fact that, in my opinion, many music makers don't know that they are working at levels reaching what is the maximum level available for the destined medium—and often above.
This is particularly true when relying solely on PPMs and mixing "in the box." It leaves a mastering engineer with very little headroom in which to work, but it also doesn't encourage steadfast production. I often receive audio that has a high level but doesn't actually sound that loud. Make sense? Probably not. Loudness, presence and energy often come through careful and skilled use of dynamics on all the different components, pulling together a mix that actually begins to sound louder in terms of energy, but only has a sensible master mix level below or near to its maximum destined medium. By using a VU meter you have a better indicator of what your limits are and can work under or up to them accordingly.
Essentially what I am trying to convey is the necessity of a good gain structure and how the VU will help.
In the digital environment there is a tendency through using PPMs—and the need to feel like you are using all the available headroom—to make every component as loud as possible. It's difficult to gauge how loud you are when you are just using PPMs, however. For instance you can have a bassline that's slow and subtle which tickles the PPMs. But you feel it can't possibly be loud enough, so you crank it up and maybe limit it so it rifles up the PPMs. But how much energy is it really carrying? Check it on a pair of VUs and you could find it's about + 8 VU. You're then trying to get all the other components to match, so everything is at a very high level. You find yourself pulling down individual faders and the master fader to have some semblance of a mix that doesn't crash into the red on the master fader PPMs. Sound familiar? Maybe, maybe not, but I know a lot of people who should know better who openly admit to this.
RMS meters exist in software form and may be a cheaper substitute. However, they tend to read higher as the relationship between RMS and VUs isn't exact. I am not pushing for them here though. I am going for the full-on accuracy in reference which high specification VUs will afford to you. I don't sit in an ivory tower, but the allure of an analogue VU lies also in its visual impetus. The ballistics are such that they follow the spurious or delicate nature of a piece with equal aplomb. The more laidback nature of the release, the polar opposite of the disco show that is a PPM.
So: Where should I connect a VU meter? The best place is across a meter output on your monitor controller or console. That way you can select what you want to meter, and meter what you're hearing. Failing this, try to connect it across a monitor DAC, or on the inputs to an ADC after an analogue chain.
There are a few models available of note. My preference is for a unit that has SIFAM VUs. They are the industry standard, meet the high specification and are very reliable. Crookwood make a model encompassing SIFAMs which represented our latest purchase. It was £295 (ex VAT) and comes with the all-important attenuation dial. Coleman Audio also makes two units. The basic MBP2 stereo meter at $525 and the multiple input MSP2V at $1,100, both available from Vintage King.