Monitoring In The Home And Recording Studio
Let’s be perfectly clear: The most important thing in your recording chain is your monitoring setup. If you can’t hear what’s going on, you can’t make proper decisions about levels, panning, equalization, or anything else. Professional studios have a big advantage in this area. In most cases, their rooms are designed around the monitoring system. The shape, size, and materials are chosen to provide the best acoustical environment at the listening position. Everything else, even the mixing console, comes second.
At the other end of the spectrum are home and project studios. They are often set up as an afterthought or wherever space permits, such as spare bedrooms, garages, or basements. And while most off-the-shelf studio monitor speakers are designed to be freestanding (meaning they don’t need to be built into walls like some studio mains), that doesn’t mean you can place the speakers just anywhere. In addition to room acoustics and speaker positioning, professional engineers have other advantages. We know systems that are unknown to most people. Fortunately, many of these tips cost little to implement, and nothing to learn, other than the time it takes to read this article.
While it may be cool to stick speakers high on bookshelves in your living room, that doesn’t fly when it comes to recording. There is little room for compromise on the following guidelines. (Hey, don’t shoot the messenger. I didn’t make the rules – I’ve just learned to live by them.)
First, speakers should be equidistant from the sidewalls. That means no corner setups. The distance between the speakers is the minimum amount you should be sitting away from them. For example, if your left and right monitors are 4' apart, you need to be at least 4' from them. This forms an equilateral triangle (where the distance between points is equal). Ideally, you should sit farther back, forming an isosceles triangle.
In terms of height, the tweeters should be targeted at your ear level. You might have to point the monitors inward a touch. Most monitors are designed vertically, with the tweeter above the main driver (see Fig. 1 below). You might be tempted to turn them sideways – be careful. Read the manufacturer’s notes regarding horizontal placement. Many speakers should not be placed on their sides. (Although some can, you may need to rotate some components of the speaker, or you may need to position the tweeters on the inside/outside. Again, you must consult your owner’s manual).
(Left) Fig. 1: Some studio monitors, such as the Mackie HR828mk2 can be positioned vertically or horizontally without compromising the stereo image
Here comes another wrinkle: The monitors should never be against the back wall. If they are close to or touching the back wall, the bass frequencies will be artificially louder. Why does this matter? You’ll think you have tons of low end in your mixes. But when you playback in your car or on your friend’s stereo everything will sound thin and wimpy. Ideally, they are several feet out from the back wall. At a bare minimum, get them 1.5' from the back wall and purchase some acoustic treatments that will trap the bass frequencies.
Common Acoustic Problems
Three common acoustic problems are comb filtering, room modes, and early reflections. Comb filtering is caused by sounds bouncing off objects that live between the speakers and your ears. This includes a mixing console, desk, computer monitor, and so on. The sound results in a warble or tremolo sound that makes it hard to tell what’s going on in the mix. The best way to avoid comb filtering is to remove unnecessary items from the immediate workspace.
Room modes (also called nodes) are frequencies that are artificially loud or soft because they are trapped by the size of your physical space. Nodes occur when a sound wave reflects off a wall and collides with the direct sound coming from the monitor. At some frequencies the reflections combine, which increases the level at that location in the room. And since every Superman has a Lex Luthor, at other frequencies the reflections can cancel the direct sound, which attenuates or eliminates that frequency altogether. As sound waves travel at about one foot per millisecond, this means most rooms will have problems between 20Hz and 200Hz – directly in bass territory.
A proper discussion of modes is beyond the scope of this article, but more information, including a calculator that can predict nodes based upon your room dimensions, can be found at mcsquared.com. Modes are often treated by constructing a room with nonparallel walls (expensive, and probably not something your wife will agree to!), treating the room with diffusers to break up standing waves, or through bass-trapping techniques.
Early reflections are a problem because they blur the sound in the room. The human brain can separate reflected sounds from direct sounds provided there is at least a 30ms delay between first hearing the direct sound and the arrival of the reflected sound. In professional recording studios, walls and furniture are angled to reflect sound away from the engineer’s head. That way, sounds that end up being bounced back to the listening position take a while to get there. This provides a more clear, focused monitoring environment. However, in a room with right-angled walls (which is just about every room), the walls behind and to the side of the speakers, as well as the ceiling, can cause early reflections that confuse the listener.
A good way to find out if a surface will cause early reflections is to sit in the mix position and have a friend walk around the room with a mirror. Start with the side walls. If you can see the monitor speaker in the mirror, that location is where there is a reflection point. Treat those areas with diffusers to help scatter the sound.
What About Acoustic Foam?
I get a lot of questions about acoustic foam – its safety and its efficacy. Many people remember the tragedy that happened at that infamous Great White concert in Rhode Island in 2003. Almost 100 people were killed when the band’s pyrotechnics caught the acoustic foam on fire, quickly burning the entire club to the ground. Older types of foam, like the kind used in that instance, had poor flame-retardant properties. However, modern brands such as Auralex perform better. You can even request independent lab results from the company. However, from an audio standpoint, you must keep in mind that acoustic foam does not work across all frequencies. In fact, most foam products do not affect some mids, let alone lower frequencies. So, acoustic foam can be great for taming early tweeter reflections, reducing slap back, and even diffusing sound, but it is not a broadband solution. To control bass, different materials and different construction methods must be used.
Bass traps are sound-treatment devices that capture low frequencies, transfer the energy into heat, and disperse it into the environment. The two most common types of bass traps are resonators and absorbers.Resonators are more focused, and are used when a specific frequency or range must be reduced. Helmhotz resonators, named after scientist Hermann von Helmholtz, can be constructed to tame specific frequencies.
Absorbers are more broadband bass traps, covering a wider range of sounds. Most absorbers are made using spun-glass insulation (commonly called 703 after the Owens Corning model number for its product) configured with a sealed membrane, which is similar to a drumhead. When the sound hits the membrane, it vibrates, causing changes in the air pressure of the tiny air pockets in the spun glass. These pockets vibrate like small springs, breaking up the original bass waves.
Integrating A Subwoofer
Reproducing low bass frequencies requires a lot of power and a speaker that can move a good deal of air. Most near-field monitors do an admirable job into the low mids (say, down to 200Hz). But you’ll need bigger speakers or a dedicated subwoofer if you want to hear what’s happening in the bass area.
The first consideration about a subwoofer is its physical location. Unfortunately, there is extensive debate regarding the proper placement of a subwoofer, especially if you’re only using one. The use of one subwoofer stems from a misnomer that bass sounds are not directional. A closer look has shown that bass sounds, while less directional than higher frequencies, do have directional properties. That’s why you see mastering studios and some recording studios use stereo subs. For home and mixing purposes, stick with one sub. You’ll be fine for now and your wallet will thank you.
The traditional method was to put the sub where the listener sits, turn it on, then crawl around on the floor and find the spot where the bass sounds the best. That’s where the sub would go. This is one way to go about it. Another is to set the sub below your mixing desk, slightly off center. Yet another is to put the sub near (but not less than 2") to one of the room’s corners. If your room is small, start with the center or off-center approach. Go through the set-up process below, and you should get good results.
Some manufacturers sell matching subwoofers, but that’s no guarantee that setting them up will be any easier than with other brands. In every case you need to make sure you have the levels and crossover points correct. What’s a crossover? A crossover is a device that routes the full-range input mix signal by frequency. Usually, low bass is sent to the subwoofer and higher signals are free to go to the main monitors. Think of it as a traffic cop for audio signals. The convenient thing is many subwoofers have crossovers built into them. You connect the main outs from your DAW to the subwoofer. Then you connect cabling from the sub to the speakers.
Next is the tricky part. There is no firm rule about what is the best frequency for bass crossover points. Most subs have variable crossover controls. This puts the responsibility for choosing the best frequency on you! To be fair, this allows for customization according to room and environment. But here is why I do not subscribe to the belief that you must pair your monitor speakers with a sub from the same manufacturer: Last year I did a sizable speaker shoot-out for a recording magazine. Some monitors came with “matching” subwoofers. When we set the subwoofer frequency at the same value suggested by the low-cut frequency on the back of the left/right monitors, the bass was wrong. In some cases there was overlap and in others there was under representation. We had to calibrate them on a case-by-case basis. The following is an abbreviated, inexpensive way to configure your subwoofer.
Things You’ll Need
- Test Tones (get them free at: realtraps.com/test-cd.htm)
- Paper, pencil, and a Sound Pressure Level Meter
Of course, you can try doing this by ear, but your results are going to be shaky, at best. An inexpensive Sound Pressure Level Meter (SPL) like the one sold at Radio Shack is fine. My meter even has a thread for mounting on a camera stand (but many cymbal stands work, and I’m certain DRUM! readers have those around).
First, connect your subwoofer and the monitors according to the manufacturer’s instructions. Second, choose a low-cut frequency on the monitors. That will be a starting point to set with your sub. If your monitor does not have cut-off filters on the back panel, you’ll need to consult the frequency-response plot in the manual, or use trial and error to determine the area where the monitor no longer produces accurate bass. Third, make sure the crossover is enabled on the sub and choose a frequency that is the same as or below the one chosen on the monitor filters. Now you’re ready to do the tests.
Mount or set the SPL meter where your head would be during mixing. Play each tone from the test-tone CD you made. On the paper, note the frequency and the level from the SPL meter. The best way is to make a grid. From left to right, note frequencies, starting with the lowest frequency on the test-tone CD and incrementing each higher frequency in the test. On the left-hand side of the paper, mark the level legend. So, running from top to bottom, mark zero at the top and increment down from there (-5, -10, and so on) until you reach -40. Leave room for values in between. Graph paper is ideal for this.
If the crossover is set up correctly, you should see minimal changes in the meter readings. If the numbers vary by a large amount, you have a problem. For example, if your crossover is set too low, there will be a gap between where the monitors stop producing bass and where the sub starts. This would be seen as a lower level, say at 90Hz, that bumps back up at 50Hz. More likely is the opposite situation: the subwoofer and the mains overlap. In this case you’ll see an increase in the areas where both speakers are doing the same job.
Calibration And Metering
The next thing I’m going to share has been known to trip up junior to moderately experienced audio engineers. What you need to remember here is that human hearing is not linear. This means our ears underestimate bass when music is played at a low level, and underestimate high frequencies when music is played at loud levels. Now you know why some stereo receivers have a loudness button – it artificially boosts the bass for listening at quiet levels. This phenomenon was first publicized in the 1930s by Bell Labs researchers Fletcher and Munson (see Fig. 2 below). They also learned that the human ear is most sensitive to tones between 1kHz and 6kHz, which explains why the telephone emphasizes those ranges – Bell Labs was searching for the best way to assure intelligibility of voice transmission.
Fig. 2: Fletcher Munson curve
This leads to the most important secret I can share with you. It’s actually a rule I have. Here goes: Never use the master fader in your DAW’s mixer as your monitor-volume controller. Ever. No exceptions. The mixer on the monitor controls the level going out to the digital master bus. There are technical implications to changing it. Leave it alone. Instead, you need to use a dedicated piece of hardware to control your volume (just like a receiver in your home stereo).
Some people use small-format mixers, however, these are not designed for transparent critical-monitoring use. They add noise and electronics that should not be in the monitor path. A better option is a dedicated control unit. On the high end of the scale are models like the Crane Song Avocet, which includes digital converters, multiple inputs, and supports multiple speakers. However, this unit is pricey for home use. Other options, such as the Mackie Big Knob, or one of my favorites, the PreSonus Monitor Station, provide a clean signal path, have room for different inputs, outputs for different speakers, and are built to last a long time. They even have talkback for performers in different rooms. Best of all, they retail in the few-hundred-dollar range.
So why do you need a monitor controller? And what about this Fletcher Munson business? A monitor controller lets you work at levels close to your system’s max – good for checking bass response, having a repeatable middle ground – good for most tasks, and a consistent low level, which can help you create mixes where vocals are well balanced against the rest of the elements. All you have to do is establish what your system’s reference zero level is, and from there you’re on your way.
Contrary to popular belief, the zero on the volume knob (max level) doesn’t really mean anything because everyone’s zero marking means something different. You may need to re-read that last sentence. It takes a while to accept. The only way to make the zero matter is to measure it against a known standard. In our case, it will be a fixed level of sound pressure at the listening position. This requires another set-up procedure, but it’s super easy.
Calibration is simple: Turn your volume control as low as it will go. Feed a pink noise signal through your speakers. (Download a free wav file at burninwave.com) Put the SPL meter at your listening position. Set it for C-weighted and start to turn up the volume knob. When the meters show 86dB on the SPL meter, mark that level on the volume knob. You now have your house zero setting. For an easier set-up experience, PC users should check out the Meter by Sonaris. (see Fig. 3 below) ) It includes automatic noise test signal calibration, works with many audio standards, and shows peak and average levels. (sonoris.nl)
(Left) Fig. 3: Sonoris Meter
In use, you now know the loudest level you should work with at your station. From here, consider two other levels, one that’s about 10—12dB quieter. Use this for your standard day-to-day work, and one 18—24dB quieter, which you can use to check vocal levels. Use the quietest level to see if the vocals sit where they need to in the mix. But remember, you can’t judge the overall mix, particularly the bass, at this low level. Fletcher and Munson explain that at lower levels our ears are not hearing the total amount of bass that’s present. Finally, check your bass and levels at the louder levels (no need to go full to zero), but try to work at lower volumes because working a full day at 86dB SPL is not good for your long-term hearing health.
What About Headphones?
Many musicians are tempted to believe they can use headphones and bypass all of the problems associated with monitoring and room acoustics. Unfortunately, this is a false hope. Headphones cannot be trusted to assess bass frequencies, nor do they reflect what your mix will sound like when it comes from two speakers.
That said, having a trusted set of headphones is a must for studio work. Things like clicks, pops, and odd sounds can sneak by on monitors, but they stick out big time in headphones. Also, things like reverb tails and other subtle effects should be checked on headphones as a second opinion. One piece of good news is that you don’t need a super expensive set of cans to get the job done. I know some recording “reference headphones” cost about $500, but many pros use less-pricey models. I personally trust a set that costs about $69 at the local pro-audio store.
It has never been so easy to get into home recording. With so many vendors offering affordable gear, you can get started with a small cash outlay. Unfortunately, this democratization of recording technology has bred the belief that you can ignore the laws of physics, especially when it comes to monitoring. From speaker placement to monitor controllers to acoustic treatments, there are some key areas that must be considered before you begin. Hopefully you’re now aware of the major pitfalls of home monitoring, and have some options for addressing them. Because when it’s all said and done, you can’t know what’s going on if you can’t hear what’s going on.