factors sfcf 0 sfcf 1 sfcf 2 and sfcf n 1 are embedded in respective frames of the sound source so the sfc factors sfcf which comprise coded digital information include corresponding sf factors such as rt reverberation time c 80 clearness and per pattern of early reflection and other sound field information as a result of the encoding of the sound source so with the sfc factors sfcf using the watermark encoder 202 the embedded results including f u2032 o f u2032 1 f u2032 2 f u2032 n 1 are obtained fig4 is a schematic diagram illustrating sound field factors representing acoustic characteristic of the sound source the reverberation time rt refers to a period over which the strength of a sound falls by 60 db from an initial strength the clearness represents a ratio of energies including a first energy from a time a sound is generated to 80 ms and a second energy from 80 ms to a time when the strength of the sound falls by 60 db the pattern of early reflection per refers to a reflection pattern after a sound is generated fig5 is a schematic diagram illustrating operation of a watermark encoder of the method of embedding the sfc factors of fig3 in the present general inventive concept a time spread echo method may be used to add the sfc factors to the sound source a kernel of the time spread echo method can be represented by the following equation where u03b4 n is a dirac delta function p n is a pseudo noise pn sequence u03b1 is an amplitude and u03b4 is a.