This standard provides methods for specifying and verifying the performance of digital professional audio equipment. Many tests are substantially identical to those used when testing analog equipment. However, because of the unique requirements of digital audio equipment and the effects of its imperfections, additional tests are irrelevant and possibly misleading when applied to digital audio deuices, they have been omitted.
ANSI S4.51-1991 history
1991ANSI S4.51-1991 Standard method for digital audio equipment - Measurement of digital audio equipment