Electronic Musician / Michael Cooper
Michael Cooper in the June, 2012, issue of Electronic Musician, writes about creating a perfect mix. In his article entitled, “Master Class – Perfecting Your Mix”, Michael goes through a series of fundamentals one should consider doing on the way to creating a good mix. Michael emphasizes that a great mix is the combination of many variables that must gel or come together at the right moment in time. Michael says that, ” a great mix happens in the last five minutes of work.”
Michael discusses headroom in our mixes, distortion, mix width, and stereo imaging. Even though these are terms associated with electronic manipulation of the signal within the mastering and mixing process, all of these terms have relevance and applicability in small room acoustics. We have to deal with distortion, sound stage width, and definitely stereo imaging in a playback environment.
Head room in our mixes, Michael explains, means that we should give our mixes as much headroom as we can. Headroom is the ability for everything to fit into the mix with plenty of space between each instrument and vocal. Multiple tracks need lots of headroom. He cautions us to be careful with faders and lowering them too far, so that they produce distortion. We should set our faders lower than the master bus to allow for plenty of room for multiple track recording to come through in its entirety, without any smothering of individual tracks.
Room Head Room
Rooms need headroom. Lets call headroom in our rooms as the ability of the room to produce all frequencies in our playback musical presentation. Middle and high frequencies must have reflection management. Vocals must be heard with every word audible in the mix. Our rooms must be able to produce all bass lines with clarity and definition. There must not be any bass boom. There must be attack and decay for each bass note frequency. How do we give our rooms more headroom?
We must first control all room resonances that are dictated by the physical dimensions of our room. First, we must choose rooms that have the proper length, width, and height to support all frequencies with as much equality as we can. If we have the right size room, we have a room that has all the resonances separated by enough distance in frequencies, so that they don’t bump into each other and cause room modes. Fighting the room in everyone of our mixes is unacceptable.
We must use powerful, low frequency, absorbers to absorb excess sound pressure energy that creates room resonances. Room resonances fill our rooms with blurring and smearing of middle and high frequencies along with bass boom because the sound pressure at certain frequencies does not fit into our room. Bass room causes bloating of our low frequencies which exaggerates certain low frequencies and smothers others.
Watch Energy Input
We can also pay more attention to the amount of energy we place in our rooms. If we have a smaller room, we have to use smaller monitors or speakers. A speaker is a box or cabinet that we put energy into. That box or cabinet can hold only so much energy because of its physical dimensions. We must inject lower amounts of energy into our smaller rooms, so that we have plenty of head room for all frequencies. Lets don’t put 6′ tall speakers in a room that has 7′ ceilings.
Michael next talks about distortion in our mixes. He tells us to check each channel for clipping and to make sure we set our clipping limiters and to check that we are not clipping in any stage of the signal chain. We should check our pre and post EQ along with post dynamics. Distortion on multiple tracks can add up and accumulate, producing harshness and glare.
Our room also has many avenues for distortion to occur within. We don’t have multiple tracks for music that can harbor distortion but we have multiple room boundary surfaces that can produce reflections at the monitoring position. We have side wall reflections that lace with the direct sound from our monitors. We must slow those side wall reflections down so that they are slower at the monitoring position by at least 15ms.than the direct sound. Rear walls that are too close to our monitoring position can produce a time delayed reflection off the rear wall at the monitoring position.
If our room is too small and room walls are to close to our board, we can get a comb filter effect. A comb filter is a series of time delayed reflections that look like a comb on an analyzer screen. With a series of reflections from a too close side wall, we get a smothering or blurring of middle and high frequencies at our monitoring position. Some frequencies will not be heard at all, since they are covered by all the multiple reflections. Reflections from our monitors to our mixing boards must also be looked at.
Michael goes on to discuss the width in our mixes. If too many tracks are panned close to center, center tracks are too loud, or tracks are too bass heavy, one can have a narrowing of the width in our sound stage presentation. If we hard pan one or more tracks, especially those with cymbals and shakers, we can begin to widen our sound stage. Michael goes on to say that if we thin out bass frequencies on stereo tracks and lower the bass guitar in the mix without adding brightness, we are on our way to eliminating a narrow image.
Room Sound Stage
Our rooms can also have an impact on our image or sound stage. Too much absorption placed on side walls can reduce our sound stage down to a narrow image. If our speakers are too close to the side and front room walls, we can actually collapse the sound stage and shrink it. Improper room width combined with over absorption can shrink our sonic presentation. If diffusion technology is used on our side walls to minimize side wall reflections, one must have enough distance between the diffusor and the listening position in order for the diffused wave form to properly form or we will get image shifting on our sound stage. It will be difficult to keep images centered.
Headroom, distortion, stereo imaging, and image width are issues all engineers must deal with during the mixing and mastering process. After all is mastered, we must play back the recording in our listening room. We must select speakers that fit our room and do not overpower it with energy. Each room size has an acoustical balance that must be achieved in the amount of energy the room can handle. Our playback rooms need the widest possible sound stage we can create, so we must be careful in our mixes not to narrow them down to the point that we minimize there presentation value in playback mode.