Figure 2 Figure 2: The impulse response in a small critical listening room before (top) and after treatment (bottom). What we need to do is make the sound appear to be coming from the live space by suppressing the early-arriving reflections from the walls of the control room, so that the sound engineer hears the ITD from the larger live space. Because our brain prioritises what it hears first, the sound will be perceived as coming from a space the size of the smaller control room (unless the live space is extremely reverberant). This is because the ITD, the Initial Time Delay, which is the time between the direct sound (which, in the control room, is coming from the loudspeakers) and the first reflection from a wall, is smallest in the control room. The first room effect the sound engineer hears is due to a reflection from a wall in the control room, rather than something from the acoustic of the live space. (Adapted from Howard and Angus, Acoustics And Psychoacoustics, Focal Press, 2009.) shows what the engineer hears in the control room when a short sharp sound is made by a musician in the live room - something like a single hit on a snare drum. Red indicates the reflections and reverberation arising from the smaller control room, and blue from the larger live space. Figure 1 Figure 1: The impulse response heard by the sound engineer in the control room, when a short sharp impulsive sound is made in a larger live space. Unfortunately, if the control room is much smaller than the live space and lacks acoustic treatment, this is not possible. The ideal control room should have a neutral acoustic where the sound engineer can ‘listen through’ to the acoustical environment of the live room. Out Of ControlĬonsider a studio engineer mixing in a control room that is smaller than the live room where the musicians are performing. A complete lack of reverberation sounds unnatural, but at the other extreme, too much reverberation can prevent aberrations from being audible to the sound engineer, leading to problems with the mix being overlooked. Rooms also have reverberance that causes a sound to linger, adding a ‘bloom’ that, in a well-designed room, subtly reinforces notes. Early reflections can also create problems with imaging, causing the exact location of sounds in your mix to become broad and blurred, and in extreme cases, being pulled away from their intended location in the stereo image. This is most evident as changes in the timbre of musical notes. At mid to high frequencies, coloration is caused by the interference between the sound reflected from the walls, floor and ceiling, and the sound coming direct from the loudspeaker to the listener. At low frequencies, the inherent resonances of the room are the cause of this coloration, with the most audible effect being a booming of certain bass notes. Acoustic engineers will talk about the room causing ‘coloration’: a change in the frequency balance of the sound, with some frequencies being boosted while others are suppressed. Rooms have a significant effect on what we hear, and this happens for all types of loudspeaker reproduction - stereo or surround. As most of us do not have the budget to use professionals, we will also look at how the design ideas can be adapted for someone creating a studio through DIY. But which is best? This guide compares different design philosophies, explaining how each affects the sound in the room and what the engineer hears as they work at the desk. Depending on who you went to, you might get offered one of a number of different design philosophies, such as Live End Dead End (LEDE), non-environment or Reflection-Free Zone (RFZ). Imagine you are creating the control room of a studio, and have the luxury of employing professionals to design and build the space to have great acoustics. But what is ‘right’, and how do you achieve it? Getting the sound in your mix space right is crucial.
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