The Art of Panning

Panning is used in two senses: fixed assignment of microphone channels to one or more loudspeaker channels, called static panning, and motion of sound sources during mixing, called dynamic panning. Of the two, static panning is practiced on nearly every channel every day, while dynamic panning is practiced for most program material much less frequently, if at all.

The first decision to make regarding panning is the perspective with which to make a recording: direct/ambient or direct-sound all round. The direct/ambient approach seeks to produce a sound field that is perceived as "being there" at an event occurring largely in front of you, with environmental sounds such as reverberation, ambience, and applause reproduced around you. Microphone techniques described in Chapter 3 are often used, and panning of each microphone channel is usually constrained to one loudspeaker position, or in between two loudspeaker channels. The "direct" microphones are panned across the front stereo stage, and the "ambient" microphones are panned to the surround channels, or if there are enough of them to the left/right and left surround/right surround channels. Dynamic panning would be unusual for a direct/ambient recording, although it is possible that some moving sources could be simulated.

The second method, called "direct-sound all round," uses the "direct" microphone channels assigned to, typically, any one or two of the loudspeaker channels.Thus, sources are placed all around you as a listener— a "middle of the band" perspective. For music-only program, the major aesthetic question to answer is, "What instruments can be placed outside the front stereo stage and still make sense?" Instruments panned part way between front and surround channels are subject to image instability and sounding split in two spectrally, so this is not generally a good position to use for primary sources, as shown in Chapter 6. Positions at and between the surround loudspeakers are better in terms of stability of imaging (small head motions will not clearly dislodge the sound image from its position) than between front and surrounds.

Various pan positions cause varying frequency response with angle, even with matched loudspeakers. This occurs due to the HRTFs:

the frequency response occurring due to the presence of your head in

the sound field measured at various angles. While we are used to the timbre of instruments that we are facing due to our conditioning to the HRTF of frontal sound, the same instruments away from the front will demonstrate different frequency response. For instance, playing an instrument from the side will sound brighter compared to in front of you due to the straight path down your ear canal of the side location. While some of this effect causes localization at the correct positions and thus can be said to be a part of natural listening, for careful listeners the effect on timbre is noticeable.

The outcome of this discussion is simply this: you should not be afraid to equalize an instrument panned outside the front stereo stage so that it sounds good, rather than thinking you must use no equalization to be true to the source. While simple thinking could apply inverse HRTF responses to improve the sound timbre all round, in practice this may not work well because each loudspeaker channel produces direct sound subject to one HRTF for one listener position, but also reflected sound and reverberation subject to quite different HRTFs. Thus, in practice the situation is complex enough that a subjective view is best, with good taste applied to equalizing instruments placed around the surround sound field.

In either case, direct/ambient or direct-sound all round, ambient microphones picking up primarily room sound are fed to the surround channels, or the front and the surround channels. It is important to have enough ambient microphone sources so that a full field can be represented—if just two microphones are pressed into service to create all of the enveloping sound, panning them halfway between front and surround will not produce an adequate sense of envelopment. Even though each microphone source in this case is spacious sounding due to their being reverberant, each one is nonetheless mono, so multiple sources are desirable.

In the end, deciding what to pan where is the greatest aesthetic frontier associated with multichannel sound. Perhaps after a period of experimentation, some rules will emerge that will help to solidify the new medium for music. In the meantime, certain aesthetic ideas have emerged for use of sound accompanying a picture:

• The surround channels are reserved typically for reverberation and enveloping ambience, not "hard effects" that tend to draw attention away from the picture and indicate a failure of completeness in the sensation of picture and sound. Called the exit sign effect, drawing attention to the surrounds breaks the suspension of disbelief and brings the listener "down to earth"—their environs, rather than the space made by the entertainment.

• Certain hard effects can break the rule, so long as they are transient in nature. A "fly by" to or from the screen is an example.

Even with the all round approach, most input channels will likely be panned to one fixed location for a given piece of program material. Dynamic panning is still unusual, and can be used to great effect as it is a new sensation to add once a certain perspective has been established.

Дата добавления: 2015-10-30