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Monitor Volume Levels
By Glen Stephan on February 6 2009 08:00 PM | Permalink | Author Info
We have set up our new studio with care and detail. We have installed our favorite near field loudspeakers as our studio monitors and have set them up accordingly in a decent-sounding room, and are ready to start work. At what volume should we listen as we mix? Is there an ideal volume for working on our mixes?

The unit of measure for measuring volume in this case is dB SPL, (Decibels in Sound Pressure Level).SPL Meter SPL can be measured with an SPL meter, which is typically a hand-held meter with built in calibrated microphone that automatically measures the volume of sounds the way a VU meter would read the electrical level of a signal. Click on Fig. 1 for detailed information on a typical inexpensive SPL meter in use in home and project studios everywhere. How loud are dBs SPL? Click Fig. 2 for a chart showing average loudness levels in dB SPL of common objects or environments, as well as their perception by or effect upon the human ear.

Most SPL meters include a selector switch for choosing between meter “weighting” characteristics. These different weighting systems, called “A”, “B” and “C”, were originally meant to very roughly mimic the ear’s overall response at different volume levels (see Fig. 3). Most measurements in our field are done with “A” weighting as a kind of de facto standard these days, and we should set our meters to A weighting when given the option.

So how loud should we be listening when mixing? There is a common and pervasive answer around the Internet that says the answer is 85dB SPL, because that’s the volume at which humans hear all frequencies equally. That’s a pretty neat answer, right? Well, like practically all short, neat answers that become so popular in chat rooms across the Internet, it’s not completely true.

Relative SPL LevelsIt is true that the human ear has different sensitivities to different frequencies at different volumes, and that, on average, it is somewhere around 85dB SPL where the sensitivity across frequencies is the most balanced. But by no means do we hear all frequencies equal. Fig. 4 shows what is called an “equal loudness contour” chart for the average human ear.

These kinds of charts are commonly referred to as “Fletcher-Munson curves”, after the engineers who first made such measurements famous back in the 1930s. Technically speaking, though, the actual original Fletcher-Munson curves have become obsolete, having been modified over the years by new research and techniques. The curves shown in Fig. 4 are based upon ISO standard 226, an international standard published in 2003.

We can see from these loudness contours that the ear’s response is not equal across frequencies at 85dBSPL, or at any other volume. It is the “flattest” at 85 dB SPL, meaning it is arguably the most equal volume across all frequencies, which seems a good reason to select 85dB SPL as a monitoring volume for mixing. But not because the response is equal, only that it comes the closest near that volume.

What’s more, these curves are averages based upon tests of many human subjects. There is no guarantee that any given single ear is going to match the response curves of Fig 3. You or I may actually hear flatter at 70dB or 100dB SPL, simply because we deviate a bit from the overall average. In fact, an individual’s ear’s deviation from these average curves can often be quite large.


It’s also important to note that 85dB SPL is fairly loud. If we refer back to our SPL loudness chart (Fig. 2), we can see that non-musical sounds at 80dB are often considered annoyingly loud. When we go above 85dB for an extended length of time, we risk damaging our hearing. A three-minute song at 85dB may be OK, but working on mixing our band’s CD all day (or for a few hours a day several days in a row) certainly can give us ear fatigue and potentially some long-term damage, where we notice it or not.

As this is a hobby or a vocation for us that relies 100% on our ability to hear well, regular or extended monitoring at 85dB SPL is not only absolutely unnecessary, but it’s probably not a very good idea.

Weighting CurvesSo where does that leave us? If not 85dB SPL, then what? Well, in fact, 85dbSPL remains an interesting reference point. It's a good reference to mark on your control room playback volume control. To do so, play some of your favorite music and hold your SPL meter (set to “A weighted”) where you head would normally be positioned when working at your desk, and adjust the playback volume until your meter is hovering around 85dB with transient peaks not rising more than a couple of dB above that on rare occasions. Note the position of your volume knob. Now do the same thing with a 1kHZ sine wave test tone. Mark the position on your volume control that falls halfway between the two points, and you’ll have a pretty good reference level.

This reference level should not be used as a constant monitoring level, however. Rather, think of it as good reminder of the approximate theoretical sweet spot for our ear’s equal loudness contours, and as a point where you can listen to your mix with detail without having to – or wanting to - crank the volume any higher for any real period of time.

In fact, much of the time we will probably want set the volume lower than that. Equal loudness contours aside – or perhaps largely because of them – the balance or imbalance between frequencies in a mix tend to lose their distinction at higher volumes. This means that what sounds good when set at 85dBSPL or higher is not necessarily what sounds good at lower volumes. On the other hand, what sounds like a good balance at lower volumes usually sounds like a good balance at higher volumes as well.

Equal Loudness ContoursThe one major exception to this balance “rule” is with bass frequencies, which require more power to drive at equal volumes as high frequencies. Because of this, mixes made only at low volumes tend to have too much bass added to them in an effort to compensate. On the other side of that coin, mixes made solely at high volumes tend to be either bass-deficient at lower volumes or wind up having vocals sounding deficient.

For these reasons, most pro engineers mix at volumes ranging anywhere from 30-65dB SPL, popping up to 85 or 90dB only temporarily to check their mixes at higher volume and make sure the mix truly “kicks”. When I mix, I have my right hand is on my CR Volume control almost as much as it is on my mouse or my faders; I'm constantly changing playback volume to match whatever it is I am actually doing at the time. Sure I will often crank it up to 85dB to check general playback, or when I get up and walk around listening back to the mix to check balance in the room, etc., but usually most of my actual "work" is done probably somewhere around 60-75dB or so, with some things going as low as 40-50dB. There are some pro engineers that would consider even my levels to be too high for their tastes.

For more on what the pros have to say on this subject, try Bobby Owsinski’s “Mixing Engineer’s Handbook”. There is an entire section containing responses to the question of monitor volume from big time mixing engineers such as George Massenburg, Elliot Scheider, Don Smith and many others.

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