570 Recording Studio Design behind-the-screen system. Note how with increasing room size (distance from listeners) and increasing reverb, it is the turnover frequency that is adjusted, not the slope. Subjective assessment has shown that the surround loudspeakers tend to need a brighter characteristic than the screen channels (i.e. less HF roll-off), which could be due to the public being closer to the sur- round loudspeakers, and hence more in their direct field. The set up of cinema monitoring systems is clearly not trivial, and as Allen pointed out `if material were to be mixed in a small room, in a large theatre it would have to have information about the content as it varied between short-duration (speech) signals, and long duration (music and possibly effects) to have perfect playback translation'. 8 Large dubbing theatres are therefore still the only viable mixing environments for high quality cinema soundtracks, because the perception of the sound between large rooms and small rooms varies so much. Of course, human perception of the relative balance of highs and lows also depends upon level, as shown in Figure 2.1, so it is essential in film production that the mixing and public performances should take place at the same levels if the equalisation compatibility is to be maintained. Unfor- tunately, after the introduction of digital soundtracks, 18 dB of headroom became available above the normal 85 dBC reference level. Many film directors began to abuse this by using it throughout the film ­ (If the plot is weak, turn the level up!) ­ which led to many cinema owners turning down the volume from the standard setting. The level reduction in the cinemas was partly due to the avoidance of distortion from some marginal reproduc-