IMPACTO AMBIENTAL

around the listener.

The perceived elevation of a sound source is not consistently repro-ducible in widely used playback systems, and has not yet become a resource for artistic expression.

Two-Channel Stereo

The first three spatial properties are realized through stereophonic sound reproduction. The spatial qualities of stereo are perceived as relationships of location and distance cues and relationships of sound sources. These create a perception of a sound stage contained within the perceived per-formance environment of the recording.

While surround sound is becoming more prevalent, two-channel sound reproduction remains the standard of the music recording industry, with monophonic capabilities still considered for AM broadcast and television sound applications. The two-channel array of stereo sound attempts to reproduce all spatial cues through two separate sound loca-tions (loudspeakers), each with more-or-less independent content (channel). With the two channels, it is possible to create the illusion of sound location at a loudspeaker, in between the two loudspeakers, or slightly outside the boundaries of the loudspeaker array; location is lim-ited to the area slightly beyond that covered by the stereo array, and to the horizontal plane. The characteristics of the sound source’s environment and distance from the listener are created in much more subtle ways by stereo, but can be stunning nonetheless.

A setting is created by the two-channel playback format for the repro-duction of a recorded or created performance (complete with spatial cues). This establishes a conceptual and physical environment within which the recording will be reproduced more-or-less accurately.

The reproduced recording presents an illusion of a live performance.

This performance will be perceived as having existed in reality, in a real physical space; as the listener will conceive of this activity in relation to their own physical reality. The recording will appear to be contained in a single, perceived physical environment. Within this perceived space is an area that comprises the sound stage.

Sound Stage and Imaging

The sound stage is the perceived area within which all sound sources are located. It has an apparent physical size of width and depth. The sound sources of the recording will be grouped by the mind to occupy a single area. It is possible for different sound sources to occupy significantly dif-ferent locations within the sound stage but still be grouped into the illu-sion of a single performance.

Imaging is the lateral location and distance placement of the indi-vidual sound sources within the sound stage. Imaging provides depth and

width to the sound stage. The perceived locations and relationships of the sound sources create imaging, as all sources appear to exist at a certain lateral and distance location within the stereo array.

Stereo Location

The stereo (lateral) location of a sound source is the perceived place-ment of the sound source in relation to the stereo array. Sound sources may be perceived at any lateral location within, or slightly beyond, the stereo array.

Phantom images are sound sources that are perceived to be sounding at locations where a physical sound source does not exist. Imaging relies on phantom imaging to create lateral localization cues for sound sources.

Through the use of phantom images, sound sources may be perceived at any physical location within the stereo loudspeaker array, and up to 15°

beyond the loudspeaker array. Stage width (sometimes called stereo spread) is the width of the entire sound stage. It is the area between the extreme left and right source images, and marks the sound stage boundaries.

Phantom images not only provide the illusion of the location of a sound source, they also create the illusion of the physical size (width) of the source. Two types of phantom images exist: the spread image and the point source.

A point source phantom image occupies a focused, precise point in the sound stage. The listener can close their eyes and point to a very precise

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Containment Walls

Sound Stage

Figure 2-1 Sound stage and the perceived performance environment.

point of little area where the source is heard to originate. Point sources exist at a specific point in space; narrow in width, and precisely located in the sound stage.

The spread image appears to occupy an area. It is a phantom image that has a size that extends between two audible boundaries. The poten-tial size of the spread image varies considerably; it might be slightly wider than a point source, or it may occupy the entire stereo array. The spread image is defined by its boundaries; it will be perceived to occupy an area between two points or edges. At times, a spread image may appear to have a hole in the middle, where it might occupy two more-or-less equal areas, one on either side on the stereo array.

The perceived lateral location of sound sources can be altered to pro-vide the illusion of moving sources. Moving sound sources may be either point sources or spread images. Point sources and narrow spread images that change location most closely resemble our real life experiences of moving objects.

Many interesting examples of phantom images can be found on The Beatles’ album Abbey Road. An apparent example of a spread image with a hole in the middle is the tambourine in the first chorus of “She Came in Through the Bathroom Window.” The lead vocal in “You Never Give Me Your Money” begins the song as a point source. The image soon becomes a spread image that gradually grows wider, ultimately occupying a signif-icant amount of the sound stage (this is partly due to the gradual addition

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Figure 2-2 Sound stage and imaging, with phantom images of various sizes.

and varying of environmental cues, which will be discussed shortly). In the second section of the work, the new lead vocal sound gradually moves from the right to the left side of the sound stage, while maintaining a spread image of moderate size.

Distance Location

Two categories of distance cues shape recorded music: (1) the dis-tance of the listener to the sound stage, and (2) the disdis-tance of each sound source from the listener.

Both of these distances rely on a perception that the entire recording emanates from a single, global environment. This perceived performance environment establishes a reference location of the listener, from which all judgments of distance can be calculated.

The stage-to-listener distance establishes the front edge of the sound stage with respect to the listener and determines the level of intimacy of the music/recording. This is the distance between the grouped sources that make up the sound stage and the perceived position of the audi-ence/listener. This stage-to-listener distance places the sound stage within the overall environment of the recording and provides a location for the listener.

The depth of sound stage is the area occupied by the distance of all sound sources. The boundaries of the depth of the sound stage are the per-ceived nearest and the perper-ceived furthest sound sources (with the depths created by their environments, discussed below). The perceived distances of sound sources within the sound stage may be extreme; they may provide the illusion of great depth and a large area, or the exact opposite.

Stage-to-listener and depth of sound stage distance cues have dif-ferent levels of importance in difdif-ferent applications. Depth of sound stage cues tend to be emphasized over stage-to-listener distance cues in many multitrack recordings; in those recordings, the cues of the distance of the source from the listener are often exploited for dramatic effect and/or to support musical ideas. In contrast, stage-to-listener distance cues are often carefully calculated in classical and some jazz recordings (especially those utilizing standardized stereo microphone techniques); in those recordings the stage-to-listener distance will not change and has been carefully selected to represent the most appropriate vantage point (the ideal seat) from which the music is to be heard.

Turning again to Abbey Road, the distance cues of the various instru-ments of “Golden Slumbers” gives the work and its companion “Carry That Weight” much space between the nearest and the furthest sources.

The orchestral string and brass instruments are at some distance from the listener and give significant depth to the sound stage, while the piano brings the front edge of the sound stage very near the listener.

Remembering that timbral detail is the primary determinant of distance location will help in accurately hearing these cues.

Environmental Characteristics

Matching a sound source to an environment with suitable sound and selecting the environment of the sound stage (the perceived performance environment) have become important parts of music recording.

Environmental characteristics have the potential to significantly impact music and the quality of the recording.

Environmental characteristics fuse with the sound source to create a single sonic impression. Its host environment shapes the overall timbre/sound quality of each sound source; this is also true for the overall program (shaped by its perceived performance environment). Envi-ronmental characteristics contribute greatly to sound quality and also play an important role in the recording’s sense of space. The characteristics provide a space for the sound sources to perform in, they supply some distance information that may be significant, and they contribute to the perceived depth of the sound stage.

The sound characteristics of the host environments of sound sources and the complete sound stage are precisely controllable. Each sound source has the potential to be assigned environmental characteristics that are different from the other sound sources. The recording process allows the potential for each sound source to be given a different environment, and for the characteristics of those environments to be varied as desired.

Further, each source may occupy any distance from the listener within the applied host environment.

The perceived performance environment (or the environment of the sound stage) is the overall environment where the performance (recording) is heard as taking place. This environment binds all the indi-vidual spaces together into a single performance area.

The environment of the sound stage and an individual environment for each sound source (or groups of sound sources) often co-exist in the same music recording. This places the individual sound sources with their individual environments within the overall, perceived performance environment of the recording. The illusion of space within space is thus created, with the following potential perceptions: