ATTENUATION QUANTITY SETTING SYSTEM

PURPOSE:To obtain a PCM signal which is attenuated by an optional quantity, by adding an subtracting a binary number corresponding to an optional attenuation quantity to and from a binary number of an input PCM signal, with respect to a signal corresponding to a segment of a high input level. CONSTITUTION:In case of giving an attenuation quantity of 2dB, a pattern whose sum of gain differences is the nearest to 2dB is searched. In an example shown in the figure, when a pattern of '10000000' is taken notice of, the sum of gain difference goes to 0.281+0.291+0.301+0.312+0.323+0.335=1.843dB. Accordingly, when only a 6-pattern portion is shifted, namely, when a binary number form '110' of 6 is added to '10000000', this value '10000110' goes to a value which is attenuated by about 2dB comparing with '10000000'. In such a way, when 6, 5, 4, 5 and 6 are added in case the lower 4 bits show '0'-4, in case said bits show 5-9, in case they show 10-12, in case they show 13-14, and in case they show 15, respectively, the attenuation of about 2dB is given consequently in each case.