Patent ID: 6668088
Filing Date: 2003-12-23
Classification: H04N

Abstract:
A compression transcoder for changing the bit rate of a compressed digital signal which has been compression encoded in a first generation quantiser Q1, having a quantisation step size q1 and a parameter &lgr;1 which controls the bounds of decision levels to be mapped onto representation levels of the quantiser, which quantiser operating on a set of transform coefficients xk representative of respective frequency indices fk to produce an amplitude y1=Q1(x), the compression transcoder comprising a second generation quantiser Q2, having a quantisation step size q2 and a parameter &lgr;2 which controls the bounds of decision levels to be mapped onto representation levels of the quantiser, in which &lgr;2 is dynamically controlled in dependence upon values from the previous encoding of the digital signal, and in which the second generation &lgr;2 value is controlled as a function:&lgr;2=&lgr;2(fk, q1, &lgr;1, q2, y1).