Sonic issues with your project studio recording? Airshow Takoma Park’s Charlie Pilzer has some answers in this two-part blog.
In this post, we address slant and bass control, two common problems I encounter with recordings from small rooms.
Slant: the mix leans to the left or to the right. Besides the aesthetic of having an uncentered mix, this is problematic in the way it affects dynamic processors. You will find it much easier to “control” or set a level on a nicely balanced mix.
Slant can be caused by inaccurate monitoring, improper acoustic treatment, arrangement of the monitors and the desk in the room – or all three.
Having and using meters can help you determine if slant is affecting your mix. Mixing to the meters won’t create a good mix but they are useful tools. Look at the average levels of a mix. If a mix sounds centered at the mix position but the mix looks unbalanced on the meters, slant may be an issue. If the main output meters indicate that the right side of the mix is “hotter” than the left, can the cause be heard? Can it be determined?
First, the monitors should be calibrated both electronically and acoustically. Run a signal of a known level through the monitor chain – for example, a signal at -15dbFS (15 db below digital full scale) which should be equivalent to 0 VU.
This can be electrically measured at the input to the amplifiers as 1.23V into a 600 ohm load. More important, the measurement should be the same on the left and right inputs to the power amp (or powered monitors). The sound pressure level of the output of the monitors can be measured with an audio level meter and should be the same from the left and the right speakers.
Second, look at the placement of the monitors in the room–they should be symmetrical to the listening position and symmetrical to the room. If the monitors are placed to one side of the room, there will be more reflection from the nearer wall and the tendency will be to adjust the mix away from that side. Reflections from any wall or the ceiling can reinforce or cancel frequencies, making it hard to determine left-right balance.
Third, consider the room acoustics. Look at the surfaces surrounding the monitor speakers. Are the surfaces of similar construction? Is one wall more reflective, diffusive or absorptive than the other?
Reflective: bounces the energy directly back into the room. This can create a “bright spot” in the sound field, possibly at the mixing position.
Diffusive: redistributes acoustic energy into a room without creating a direct reflection. Mixing in a “dead” room can be as difficult as mixing in an overly reflective room. Acoustic tuning of a room is a complex subject (and will be addressed in a future blog post).
Absorptive: reduces the energy returned into the room. Absorbers can be broad, covering the entire frequency range, or they can be frequency-specific.
The general principal is the same as having the speakers symmetrical with a room. The idea is to keep the sound of a room symmetrical. As an example, a large window to one side of a mixing room or a large expanse of drywall can create reflections. Although the speakers are symmetrical along the front wall, the result will be an asymmetrical listening position–possibly fooling the mix engineer into making one side of the mix louder than the other.
Bass control issues arise when you have too much or too little bass in the mix.
Hearing the proper level of bass is difficult in a studio with a small footprint. More modest or physically smaller monitors do not cover the bottom octave (fundamental) of bass instruments, nor the full range of a kick drum. As a result, a mix engineer may put more bass energy into a mix than is needed. Alternatively, a small room can create a “buildup” of energy at bass frequencies, leading the engineer to reduce the level of bass below the level actually needed in the mix.
Listen to the mix on other monitor or sound systems in other rooms–on headphones and perhaps in an automobile. Does the mix generally have too much or too little bass? If the bass seems to dominate the mix or the mix is “boomy,” then the studio room and monitors do not generate enough bass energy. If the result is too little bass or a “weak” sounding bass, then the room may be creating a false sense of the bass levels.
Go back to the mix room. Listen to other recordings similar to the mix in process. Does there seem to be too much bass? Or too little? Or is it muffled?
As with slant and panning, placement of the monitor system in a room can make a big difference in hearing your bass accurately. Try moving the speakers away from the front wall by one foot or moving closer to the wall by a foot. How does that affect the bass? Try something radical like placing the mix position facing into a corner of a room and the monitor speakers symmetric to the corner. (Hint: It might be necessary to deaden the corner itself.)
The results will be complementary: if a CD recording plays back with too little bass at the mix position, then the mix will probably have too much bass when taken out of the mix room. Adding a subwoofer can improve the situation, but the subs need to be tuned to the proper level and proper crossover frequency and this can require some experimentation.
If the room is creating a sense of more bass in the mix, the solution may involve some acoustic tuning. Bass frequencies can “build up” at wall boundaries and in corners. Acoustic absorption of low frequencies can help the situation–particularly at the front wall-ceiling junction and the two front wall corners. Adding diffusion to the wall behind the mixer can keep the energy of the sound in the room but help spread it to prevent reflections.
There are numerous resources on room acoustics that address these and other small room acoustic issues in depth:
- Wikipedia has introductory (although not always thorough) articles on the subject.
- Manufacturers like RPG and Auralex and Sonnex have information about acoustic treatments
- Publishers Focal Press and Mixbooks have whole books on the subject of proper acoustic treatment of rooms.
- Forums that address a variety of small room sonic issues include those at retailers Sweetwater, Full Compass, and Musician’s Friend.
- Websites that we find helpful include Gearslutz.com, recording.org, or homerecording.com.
- Google is a good place to expand your search.
At Airshow, we’re fortunate to have large rooms, full-range monitoring and rooms that are well-tuned and accurate. Airshow clients often schedule a short “listening session” with an Airshow mastering engineer in order to reality-check their mixes before they consider their mixing work finished.