2.5.8. Sample de-quantization

Requantization is the first operation necessary to bring back the samples to the original PCM form. The samples are extracted from the FRAME and read. Care is taken to separate the grouped samples (they had been grouped if bit allocation prescribed a number of 3, 5 or 9 quantization steps) with the following algorithm:

c : value of the three samples grouped

s[0..2] : value of the three samples after the extraction from the group

FOR (i=0 ; i<3 ; i++)

{ s[ i ] = c MOD (number of steps)

c = c DIV (number of steps)

}

The number of bits taken by each sample follows directly from the number of quantization steps. For each sample, the MSB must be inverted to get back the original value.

Once all 1152 samples have been reobtained, their requantization is performed by computing:

s'' = C * (s''' + D)

where s''' is the quantized value and s'' the de-quantized; coefficients C and D depend on the quantization steps, as shown in the following table:

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