Abstract: A steel plate according to an aspect of the present invention has a predetermined chemical composition, an index Q obtained by Equation (1) is 0.00 or more, a carbon equivalent Ceq (%) obtained by Equation (2) is less than 0.800%, a ratio of a difference between a hardness at a surface layer portion and a hardness at a thickness center portion to the hardness at the surface layer portion at a room temperature is 15.0% or less, the hardness at the suffice layer portion at a room temperature is 400 or more in terms of Vickers hardness, and a steel thickness is 40 or more. Q=0.18?1.3(logT)+0.75(2.7×[C]+[Mn]+0.45×[Ni]+0.

Abstract: A bit allocation processing section allocates quantization bits to each subband on the basis of the information of each SMR input from a psychoacoustic model processing section by using a bit allocation table that associates the sound information amount (SMR) of each audible sound with a bit allocation count, thereby allocating the quantization bits indicated by the bit allocation table to each subband. By performing this processing once for each subband, bits can be allocated to each subband. This makes it possible to eliminate the necessity to perform a loop process and shorten the arithmetic processing time required for bit allocation processing.

Abstract: A method of producing steel plate having a low yield ratio and high strength and a dual-phase mixed microstructure of ferrite and second-phase carbide comprises heating to at least 950.degree. C. low-carbon slab steel having 0.30% or less carbon, 0.05 to 0.60% silicon, 0.5 to 2.5% manganese, and 0.01 to 0.10% aluminum as the basic components, with the balance being iron and unavoidable impurities, or low-carbon low-alloy slab steel comprising in addition to the above basic components one or more elements selected from copper, nickel, chromium, molybdenum, niobium, vanadium, titanium, boron and calcium, hot rolling it, reheating it and tempering it.