3 Definitions, symbols and abbreviations

26.4023GPPAdditional decoder toolsEnhanced aacPlus general audio codecGeneral audio codec audio processing functionsTS

3.1 Definitions

For the purposes of this TS, the following definitions apply:

band: (as in limiter band, noise floor band, etc.) a group of consecutive QMF subbands

envelope scalefactor: an element representing the averaged energy of a signal over a region described by a frequency band and a time segment

frequency band: interval in frequency, group of consecutive QMF subbands

frequency border: frequency band delimiter, expressed as a specific QMF subband

noise floor: a vector of noise floor scalefactors

noise floor scalefactor: an element associated with a region described by a frequency band and a time segment, representing the ratio between the energy of the noise to be added to the envelope adjusted HF generated signal and the energy of the same

SBR envelope: a vector of envelope scalefactors

SBR frame: time segment associated with one SBR extension data element

SBR range: the frequency range of the signal generated by the SBR algorithm

subband: a frequency range represented by one row in a QMF matrix, carrying a subsampled signal

time border: time segment delimiter, expressed as a specific time slot

time segment: interval in time, group of consecutive time slots

time / frequency grid: a description of SBR envelope time segments and associated frequency resolution tables as well as description of noise floor time segments

time slot: finest resolution in time for SBR envelopes and noise floors. One time slot equals two subsamples in the QMF domain

3.2 Symbols

For the purposes of this TS, the following symbols apply:

E_Orig has L_E columns where each column is of length N_Low or N_High depending on the frequency resolution for each SBR envelope. The elements in E_Orig contains the envelope scalefactors of the original signal.

the output sampling rate from the SBR Tool.

internal sampling frequency of the SBR Tool, twice the sampling frequency of the core coder (after sampling frequency mapping, ISO/IEC 14496-3:2001, Table 4.55). The sampling frequency of the SBR enhanced output signal is equal to the internal sampling frequency of the SBR Tool, unless the SBR Tool is operated in downsampled mode. If the SBR Tool is operated in downsampled mode, the output sampling frequency is equal to the sampling frequency of the core coder.

has two column vectors containing the frequency border tables for low and high frequency resolution.

f_TableHigh is of length N_High+1 and contains frequency borders for high frequency resolution SBR envelopes.

f_TableLow is of length N_Low+1 and contains frequency borders for low frequency resolution SBR envelopes.

L_E number of SBR envelopes.

L_Q number of noise floors.

N_Q number of noise floor bands.

number of frequency bands for low and high frequency resolution.

numTimeSlots number of SBR envelope time slots that exist within an AAC frame, 16 for a 1024 AAC frame and 15 for a 960 AAC frame.

offset-values for the SBR envelope and noise floor data, when using coupled channels.

Q_Orig has L_Q columns where each column is of length N_Q and contains the noise floor scalefactors.

frequency resolution for all SBR envelopes in the current SBR frame, zero for low resolution, one for high resolution.

t_E is of length L_E+1 and contains start and stop time borders for all SBR envelopes in the current SBR frame.

t_Q is of length L_Q+1 and contains start and stop time borders for all noise floors in the current SBR frame.

Y is the complex output QMF bank subband matrix from the HF adjuster.

3.3 Abbreviations

For the purposes of this TS, the following abbreviations apply.

AAC Advanced Audio Coding

aacPlus Combination of MPEG-4 AAC and MPEG-4 Bandwidth extension (SBR)

Enhanced aacPlus Combination of MPEG-4 AAC, MPEG-4 Bandwidth extension (SBR) and MPEG-4 Parametric Stereo

MPEG Moving Picture Experts Group

SBR Spectral Band Replication