4.1.5 Frame energy calculation and quantization

3GPP46.020Half rate speechHalf rate speech transcodingRelease 17TS

The unquantized value of R0, R(0), is computed during the computation of the short term predictor parameters.

(27)

where (i,k) is defined by equation (5). R(0) is then converted into dB relative to full scale (full scale, Rmax, is defined as the square of the maximum sample amplitude).

(28)

RdB is then quantized to 32 levels. The 32 quantized values for RdB range from a minimum of ‑66 (corresponding to a code of 0 for R0) to a maximum of ‑4 (corresponding to a code of 31 for R0). The step size of the quantizer is 2 (2 dB steps). R0 is chosen as:

R0 which minimizes abs(R0 – (RdB + 66)/2) (29)

where R0 can take on the integer values from 0 to 31 corresponding to the 32 codes for R0.

Decoding of the R0 code is given by:

(30)