What is critical listening?
Throughout our daily activities, our sense of sound plays a remarkable role in our perceptions and abilities relating to the world around us. From the obvious use in communication to the more subliminal effects such as balance and proximity, our interpretation of sound, aside from instinctual reactions, is learned from the time we're born. A good analogy of the difference between casual listening and critical listening is the sound of the surf crashing as you enjoy a day at the beach or the sound of an intruder picking the lock on your front door. All attention is focused on the sound of the intruder, whereas the surf is background. Training and experience play the important role when it comes to critical listening. Early Native Americans depended on the trained ear for survival when listening for prey or predator.
Let's apply this brief introduction to the listening environment of the recording studio. Training to understand image, phase, frequency and amplitude are the stepping stones to successful listening, recording and mixing. Balance is a word you will see repeatedly in this article. Critically listening for the balance of artifacts that cumulatively create the material you listen to is the goal. The mind must be trained to interpret and isolate the intricacies of the material you are inspecting. The purpose of this article is to help point the way to a better understanding of what you are or are not hearing in hopes of enabling more articulate expression sonically.
There are many choices when it comes to speakers, amplifiers, preamplifiers, cable, connectors, etc.. The choice comes down to personal preference and priorities. Hopefully after reading this article, your choice in monitors will be easier and more confident. There are several things to consider when choosing a monitor. I will go over the qualities of monitors to consider in what I believe to be the order of priority.
Phase is typically my first priority. The way in which sound arrives in the time domain is what gives us the perception of space and placement. Sound travels relatively slow (about 1130 feet per second which is like a hot loaded 38 special), so time plays an extremely important role. To recreate the most natural reproduction of sound, the recreation of the time arrival across the frequency spectrum is crucial. Consider that every millisecond of deviation is 1.13 feet of misplacement. Think about only misjudging the edge of a cliff by 1.13 feet. or being only a few inches in the way of a speeding train. Having sound arrive at your ear with as much of the time information intact is the idea. If a specific frequency or range of frequencies is even ever so slightly out of time, the reproduction of the source is distorted. A visual would be like separating the part of the snare that creates say, 1KHz and moving it an inch or two closer or further away. As unnatural and out of focus as that would look, it sounds at least as wrong. Try to select a monitor that is capable of producing accurate phase. With this achieved, imaging becomes most accurate.
Frequency response is a very close second in the priority list. The balance of amplitude across the sound spectrum is very important in the way our brain interprets sound. How much rumble can mean how big of an explosion and how much crack can mean how hard of an impact. Too much sibilance? may go undetected if the high end is too recessed or sibilance that is not actually there may be detected if the high end is boosted. The better drivers are typically more capable of producing fairly linear response with less manipulation from the crossover. The less in the path usually means the less phase shift and also the less artificial characteristics.
Next on the list is what I call friendliness. All those buzz word like "silky", "warm", "rich", "sweet", "fat", etc.. I love all that stuff, but if I'm making critical decisions, I only want to hear it if it's really there. I have worked on speakers that make mistakes sound good. That's a lot of fun in the living room, but in the studio I don't mind earning a great mix.
Whatever monitors you prefer, understand what you are hearing is the bottom line. The more in focus the picture, the more clearly the imperfections show and the more effectively they can be understood and dealt with.
In this article I am concentrating on the control room mainly. However, critical listening is not by any means limited to the control room. We are talking about tools. The microphone is the main ingredient in capturing sound for reproduction. Critical listening when positioning microphones can definitely make or brake a tracking session. Use your ears to determine what you are trying to capture. Once you hear the spot you like, place the microphone there. If you choose the right microphone, it's a done deal. Plenty of High quality microphones and pre amps and really knowing them is key. Not sure how to rewrite this last sentence.
By choosing the right microphone and position, the need for equalization and processing is lessened thus creating a more accurate representation of the subject being recorded. In this situation, the processing may be used for effect rather than repair. Through experience, we determine our likes and dislikes which dictate our decision making when search for sounds. The more accurate your reference, the better your choices in the recording process and the more control in the mixing process, so choose your weapons carefully.
This is where we get down to the goods. You can have the most perfect monitor system on the planet, but if the room is wrong and/or the speakers are installed or positioned improperly, the response at the listening position can be disastrous. This section of the article is most valuable. We are talking about critical listening and have discussed why it is important to have clarity and resolution, etc., but how do we create a situation where critical listening is possible? How can we trust what we hear? The key to these questions lies in the acoustical environment, and how it couples with the equipment.
Let's assume you have selected your monitors. The first step is properly positioning the speakers. Be aware of boundaries around the speakers and how they affect the response, especially when positioning your near and mid field speakers. The more non-directional low frequency energy wraps around the backside of the monitor and redirects from the front part of the room back to the listener, but delayed, causing interference with the initial source. There are some excellent software programs that can assist you in determining speaker and listener positions in rooms with parallel walls. At this point I haven't heard of software for irregular shaped rooms. The good old fashion way to determine speaker and listener position is to run an RTA with the microphone where you want to sit and move the speaker in 6" increments until the low end gets as flat as possible. The opposite approach may also be applied. Move the microphone while the speaker is stationary. It is a bit of work, but it's worth it.
The dispersion characteristics of the monitor must be taken into account as to realize any potential interference in the room. If possible, acquire polar plots of the speaker so you may understand which frequencies are colliding with which objects or boundaries. First reflections must be eliminated to help ensure that you hear only the speaker. Consider the mid and high frequencies to have a light beam like characteristic. If a surface is hard or reflective, the light will reflect off the surface at the same angle it hit. A simple ray tracing diagram can be of assistance to recognize potential problems (DIAGRAM 1). Try to keep equipment racks and other furniture below the line of fire. Not all hard surfaces are bad. Some hard objects may have irregular shape thus causing diffusion which in many cases, if in the proper location, can be an enhancement (Peter D'Antonio of RPG has written many valuable papers on the subject of diffusion as well as manufacturing several diffusion devices).
It is also very important to understand the on and off axis response of the speaker. Some speakers are designed to be a bit off axis, while others get the optimum results when the listener is perpendicular to the tweeter. In most situations, it is preferred to have good off axis response to achieve a wider listening area.
The orientation of the drivers (woofer to the tweeter etc.) is critical to the time arrival and should dictate how the speaker is positioned. The phase characteristics will vary from speaker to speaker depending on delays caused electronically and the physical alignment of the drivers, so I suggest acoustical measurements to determine the proper alignment to the drivers for the best phase response.(I'm a fan of the "SIA SMART" software. It provides phase and frequency as well as room decay information. The only complaint is that it's not available for Mac.) One big mistake I see often is to lay two way? near field monitors in such a way that the woofer and tweeter are horizontal. This creates a time domain problem where the accurate listening spot is about the size of a dime. Iin the case of discrete monitors (separate woofer and tweeter as opposed to coaxial or dual concentric where all frequencies have a common point as the source). With dual concentric speakers, the vertical and horizontal response is similar, Determine the best orientation between the woofer and tweeter for optimum phase and frequency response and focus that point on the same plane as your ears. By having the woofer and tweeter vertical, you can move from left to right across the board with little deviation from the, shall we call it the "Phase Plane"TM(<--private joke). If the drivers are horizontal, moving left to right will cause vary drastic deviations in the time arrival (DIAGRAM 2). Don't get stuck on what you have seen. There's a good chance it was wrong. If being more on axis to the tweeter gives better response, flip the speaker upside down. It might look a little funny but more often than not that is the better position for near fields on a meter bridge that's a little high. As far as soffet mounted main monitors go, be careful. It's much more difficult to tear the front wall apart then to flip a little near field around. Be sure you understand the monitor before you build a home for it.
About Low Frequency
Out of control low frequency can definitely ruin your day. In fact, control of the low frequency is the foundation of a good critical listening space. I don't want to get too far into design in this article, but be very aware that the low frequency needs to be understood and treated properly to have a critical listening environment. Where mid and high frequencies act more like light, low frequency response is dictated by wave acoustics. The relationship of the wavelength to the room dimension does not allow for the directionality required in-ray acoustics to be applied. The dimensions of the room dictate the root and thus the harmonic frequencies that will resonate in that room. Low frequency resonance tends to accumulate in the far boundries of the room, like the corners of a room or where acute angles may exist. Also where parallel surfaces exist, standing wave will occur. This energy loading and crashing back into itself is a bit like a train wreck. The effects of this occurrence disturbs the entire spectrum both harmonically and in the perception of balance across the frequency spectrum. The key is to eliminate the interference without overly effecting the efficiency or musicality of the room. The same way an accomplished martial artist can use or redirect the energy of an attacker to control or subdue with the most efficient use of his own energy, sound energy should be treated in a similar fashion where force is used appropriately.
It all comes down to balance. One of the most powerful governing laws of the universe. Balance determines the state of just about all aspects of our universe. When things are in balance, optimum energy is achieved. When balance is compromised, the chain reaction is potentially devastating and very difficult to recover from. I'm going on a bit of a tangent, but if your attention span can handle it, there is a valuable point here. Think of a house of cards, or a chain of dominoes. We all know what happens when either looses balance. A child learning to ride a bicycle will over correct in attempt to achieve balance.
When balance is understood, the amount of correction, if needed at all, is precise. Let's go a step further. In the human body, if one has good posture, there are great skeletal, muscular, neurological and spiritual benefits. A better way to understand this is to consider poor posture. The skeletal system is stressed. Certain muscles are strained to compensate for the weakening of less used muscles. Emotional balance becomes compromised as a result of fatigue. Neurotransmission becomes less acute. The flow of internal energy is constricted causing premature deterioration of the internal organs. Over correcting to counter one problem creates another. This can all be the result of poor physical balance or bad posture.
The listening space can be considered a body or an entity, and is equally sensitive to balance. It is subject to chain reactions if precision in balance is not considered. An anechoic chamber will give the most accurate representation of a speaker but be horribly uncomfortable to be in with the worst case of efficiency. An echo chamber will be amazingly efficient but equally as uncomfortable and extremely confused. Balance. Carefully creating a space where reverb times across the spectrum are similar and interference is minimized. Tight controlled low frequency at the expense of a bit of efficiency is a trade well worth doing. If it comes to a choice, give up some efficiency for accuracy. You can always get a bigger truck with more horsepower, but only give up enough, not too much. A clever balance of reflection, absorption and diffusion will result in excellent resolution with the least amount of efficiency sacrificed. When all things are in balance, optimum energy is achieved. Focus on the intricacies becomes much more effortless.
In this situation true critical listening can be achieved.