5.7 Data quantization

26.4043GPPEnhanced aacPlus encoder Spectral Band Replication (SBR) partEnhanced aacPlus general audio codecGeneral audio codec audio processing functionsRelease 17TS

The spectral envelope scalefactors are quantized in 3dB steps or in 1.5dB steps, dependent on the time frequency resolution of the current SBR frame, and bs_amp_res. For the case where there is only one SBR envelope per SBR frame and of SBR frame class FIXFIX, 1.5 dB steps are always used, disregarded the value of bs_amp_res.

For mono and stereo without channel coupling the quantization is done according to:

where and

For the coupled channel mode, the left channel is quantized according to the above, while the right channel should be quantized according to:

The noise floor scalefactors data is always quantized in 3dB steps. For stereo without channel coupling and for mono the channels are quantized according to:

,

where shall be limited to the interval .

For coupling however, the right and left channels are quantized according to:

,

where

shall be limited to the interval and is limited to the interval .

In the case of coupling, the and values shall be quantized to multiples of two, e.g. .