Digital coding ranges for use in an all-digital sound studio complex.
This Report considers principally the sound-signal coding-range requirements for different applications in a digital studio complex, excluding the internal requirements of processing equipment, such as control desks, etc. It is suggested that the most demanding requirements should be met by a coding standard of 22 bits/sample for uncontrolled sound signals. With manual control the coding range may be reduced considerably, but should not be reduced below 18 bits/sample within the studio complex in order to provide a coding margin for possible post-production processing of the signal. This margin comprises 2 bits (12dB) of headroom to accommodate signal peaks exceeding the nominal maximum level as well as least-significant bits to preserve a low level of quantising error. At the output of the studio centre, when no further processing of the signal is envisaged, the coding may be reduced to 16 bits/sample, or to 14 bits/sample with the aid of digital limiting for distribution. It is noted that 22 bits/sample linear coding is well beyond the capability of present analogue/digital converter technology, but it is envisaged that floating-point converters approaching this standard, with a resolution of, say, 15 bits/sample would be adequate and will be developed in the future. Floating point techniques may have further application in digital recording, to provide equivalent wide-dynamic-range recording facilities.
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