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The stereo microphone array can significantly alter the sound source in a number of ways. All stereo microphone techniques have their own unique characteristics; as such their own inherent strengths and weaknesses. The inherent sound qualities of the stereo microphone arrays can be used to great advantage if the recordist understands and is in control of their sound qualities. The recordist will need to become aware of the sound qualities of each of the various arrays, evaluating their abilities to function according to the following list of variables, in the context of the above mentioned microphone placement variables.
• Perceived listener to sound stage distance
• Amount and sound quality of the environmental
characteristics of the performance space
• Perceived depth of the ensemble, sound source or
sound stage
• Perceived width of the sound source or the sound stage
• Definition and stability of the lateral (stereo) imaging
• Musical balance of the sound sources in the ensemble
• Sound qualities of the entire ensemble or of specific
sources within the ensemble
The recordist will often use the concept of the ideal seat when determining the placement of a stereo microphone array. The placement of the array will theoretically provide sound qualities that are most desirable for the particular ensemble, performing a specific piece of music, in the most appropriate performance space. The ideal seat is related to the concept of creating a perfect performance; the recordist will seek to balance the hall sound with that of the ensemble, capture an appropriate amount of timbre definition from the ensemble, retain all performed dynamic relationships, and establish desirable and stable spatial relationships in the sound stage.
Many stereo microphone techniques have been developed. Among the most commonly used are:
• X-Y coincident techniques
• Middle-Side technique (M-S)
• Blumlein Pair (crossed figure-eights)
• Near coincident techniques (NOS and ORTF)
• Spaced omni-directional microphones
• Spaced bi-directional microphones
• Binaural system (artificial head)
• Sound field microphone system
Accent microphones are often used to supplement the stereo microphone techniques, above (with the exception of the specialized binaural and sound field recording systems). These are microphones that are dedicated to capturing a single sound source, or a small group of sound sources, within the total ensemble being recorded by the array. The accent microphones are placed much closer to the sound sources than the array, and may cause the recordist to consider some of the close micing variables discussed above.
At times, secondary stereo arrays can suitably function as a set of accent microphones. This is especially usable with large ensembles (such as an orchestra plus chorus). The recordist must be aware of delay times between the arrivals of the accent array(s) and the overall array signals. These time differences may be minimized through applying delay units to the secondary array(s); thus avoiding comb filtering distortions.
When using accent microphones in conjunction with stereo microphone arrays, the accent microphones are most often used to complement the array. They assist the overall array by bringing more dynamic presence and timbre definition to certain sound sources in the ensemble, and they allow the recordist some control over the musical balance of the ensemble. Accent microphones also create noticeable time differences between the arrival of the sound source(s) at the stereo array, and the arrival of the sound source(s) at the accent microphone.
Adding accent microphones will diminish the realistic nature of the stereo microphone array, in accurately capturing the performance (while attempting to improve the sound present in the hall). Accent microphones will alter time cues and dynamic relationships noticeably, making the sound source(s) captured by the accent microphone significantly more prominent in the musical texture.
Equipment Selection: Application of Inherent Sound Quality
With a clear understanding of the desired sound qualities of the individual sound sources and the entire recording project, the recordist must determine which pieces of the equipment s/he will utilize to achieve the desired result. The recordist will approach this problem by evaluating the inherent sound characteristics of the available individual devices, and the inherent sound characteristics of the technologies of those devices, against the unique needs of the individual project.
Digital recording, processing, editing equipment is not necessarily "better" than analog equipment, in relation to its potentials for artistic expression; nor is the opposite true. No technology is inherently better suited, than another, for generating, capturing, shaping, mixing, processing, combining, or recording sound.
Analog technology has certain inherent sound characteristics. Digital technology has certain inherent sound characteristics. The characteristics of one technology may or may not be appropriate for the particular project. Inherent sound qualities are inherent sound deficiencies if they work against the sound quality the recordist is trying to obtain. Inherent sound qualities are desirable if they produce the desired sound quality for the recording.
It is difficult to make generalizations as to the characteristics of analog versus digital technology. The sound qualities of both technologies vary widely depending on the particular unit, and the integrity of the audio signal within the particular devices. An eight-bit digital system is significantly less accurate and flexible than a 32-bit system. A consumer-model analog system is significantly more noisy and less accurate than a professional unit.
Differences often exist between the two technologies in: (1) their abilities to accurately track the shape of the waveform (especially the initial transients of the sound wave, in both technologies); (2) their abilities to process all frequencies equally well (especially frequency response problems of analog, or quantization errors in digital); (3) their ability to store the waveform without distortion from the medium (especially tape hiss, or A/D and D/A conversion errors); (4) their ability to alter the waveform in precise increments, and to precisely repeat these functions (a measure of signal processors); (5) their ability to perform repeated playings, successive generations of copying, and long-term storage with minimal signal degradation (a measure of recording formats). Many other, more subtle, differences exist, especially between specific devices of each technology.
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