2 Monitoring

Tips from This Chapter

• Monitoring affects the recorded sound as producers and engineers react to the sound that they hear, and modify the program material accordingly.

• Just as a "bright" monitor system will usually cause the mixer to equalize the top end down, so too a monitor system that emphasizes envelopment will cause the mixer to make a recording that tends toward dry, or if the monitor emphasizes imaging, then the recording may be made with excessive reverberation. Thus, monitor systems need standardization for level, frequency response, and amount of direct to reflected sound energy.

• Even "full-range" monitoring requires electronic bass management, since most speakers do not extend to the very lowest audible frequency, and even for those that do, electrical summation of the low bass performs differently than acoustical addition. Since virtually all home 5.1-channel systems employ bass management, studios must use it, at the very least in testing mixes.

• Multichannel affects the desired room acoustics of control rooms only in some areas. In particular, control over first reflections from each of the channels means that half-live, half-dead room acoustics are not useful. Acoustical designers concentrate on balancing diffusion and absorption in the various planes to produce a good result.

• Monitor loudspeakers should meet certain specifications that are given. They vary depending on room size and application, but one principle is that all of the channels should be able to play at the same maximum level and have the same bandwidth.

• Many applications call for direct-radiator surrounds; others call for surround arrays or multidirectional radiators arranged with less direct than reflected sound at listening locations. The pros and cons of each type are given.

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• The AES and ITU have a recommended practice for speaker placement in control rooms; cinema practice differs due to the picture. In control rooms center is straight ahead; left and right are at ±30° from center; and surrounds are at ±110° from center, all viewed in plan (from overhead). In cinemas, center is straight ahead; left and right are typically at ±22.5° from center (the screen covers a subtended angle of 50° for Cinemascope in the best seat); and the surrounds are arrays. Permissible variations including tolerances and height are covered in the text.

• So-called near-field monitoring may not be the easy solution to room acoustics problems that it seems to promise.

• If loudspeakers cannot be set up at a constant distance from the principal listening location, then electronic time delay of the loudspeaker feeds is useful to synchronize the loudspeakers. This affects mainly the inter-channel phantom images.

• Low-Frequency Enhancement (LFE), the 0.1 channel, is defined as a monophonic channel having 10dB greater headroom than any one main channel, which operates below 120 Hz or lower in some instances. Its reason for being is rooted in psychoacoustics.

• Film mixes employ the 0.1 channel that will always be reproduced in the cinema; home mixes derived from film mixes may need compensation for the fact that the LFE channel is only optionally reproduced at home.

• There are two principal monitor frequency response curves in use, the X curve for film, and a nominally flat direct sound curve for control room monitoring. Differences are discussed.

• All monitor systems must be calibrated for level. There are differences between film monitoring for theatrical exhibition on the one hand, and video and music monitoring on the other. Film monitoring calibrates each of the surround channels at 3dB less than one front channel; video and music monitoring calibrates all channels to equal level. Methods for calibrating include the use of specialized noise test signals and the proper use of a sound level meter.