2010318163752818

Short block:
N_FR 128/120 MDCT block size
Table 4.141 – Parameter table for the enhance and enhance_960 mode
ISO/IEC 14496-3:2005(E)
Parameter
Common:
Value Meaning
AMP_MAX 8000 Maximum amplitude in the mu-law coding of the frame gain
AMP_NM 1024 Normalized amplitude of flattened coefficients
FW_ALF_STEP 0.5 MA prediction coefficient for the envelope coding
MA_NP 1 MA prediction order (LSP coding)
MU 100 Parameter mu in the mu-law coding of the frame power
N_PR 20 LPC order
NUM_STEP 256 Number of gain-quantization steps
STEP AMP_MAX / (NUM_STEP- Step width of gain-quantization
1) = 31.37
SUB_AMP_MAX 6000 Maximum of subframe-gain to frame-gain ratio
SUB_AMP_NM 1024 Normalized subframe amplitude of flattened coefficients
SUB_GAIN_BIT 4 Number of bits for the subframe gain coding
SUB_NUM_STEP 16 Number of sub-gain-quantization steps
SUB_STEP SUB_AMP_MAX/ Step width of sub-gain-quantization
(SUB_NUM_STEP-1)= 400.0
Long block:
FW_CB_LEN 7 Envelope code vector length
FW_N_BIT 6 Envelope code bits
FW_N_DIV 7 Number of division in the envelope coding
N_CRB 42 Number of bark-scale subbands
N_FR 1024/960 MDCT block size
Short block:
N_FR 128/120 MDCT block size
4.6.11 Filterbank and block switching
(Similar to ISO/IEC 13818-7)
4.6.11.1 Tool description
Table 4.142 – Values of isp[]
split_num isp[split_num]
0 0
1 5
2 14
3 20
The time/frequency representation of the signal is mapped onto the time domain by feeding it into the filterbank
module. This module consists of an inverse modified discrete cosine transform (IMDCT), and a window and an
overlap-add function. In order to adapt the time/frequency resolution of the filterbank to the characteristics of the
input signal, a block switching tool is also adopted. N represents the window length, where N is a function of the
window_sequence (see subclauses 4.5.2.3.3). For each channel, the N/2 time-frequency values Xi,k are
transformed into the N time domain values xi,n via the IMDCT. After applying the window function, for each channel,
the first half of the zi,n sequence is added to the second half of the previous block windowed sequence z(i-1),n to
reconstruct the output samples for each channel outi,n.
4.6.11.2 Definitions
window_sequence 2 bit indicating which window sequence (i.e. block size) is used.
window_shape 1 bit indicating which window function is selected.
© ISO/IEC 2005 — All rights reserved 171