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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - HD RADIO
55
Figure 4.16
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
64 96 128 160 192
kbps
MPEG AAC
Dolby AC3
Lucent PAC
MPEG L2
Source: Journal of the Audio Engineering Society, Vol. 46, No. 3, March 1998, p. 164.
Where the signal quality refers to the Subjective Difference Grade ITU scale (ITU-R
BS.562) as follows:
0 = Imperceptible
-1 = Perceptible but not annoying
-2 = Slightly annoying
-3 = Annoying
-4 = Very annoying
Not shown in the previous graph is the usage of the Sub-band replication (SBR)
technique. This technique allows for a higher coding efficiency by coding the lower
bands (up to 8 kHz to 12 kHz) using a basic codec (MPEG AAC, L2 or others) and
replicating the upper frequency using statistical and predictive information. This
technique usually demonstrates an increase in efficiency of up to 30% and it is
generally backward compatible with the source codec. The iBiquity Digital HDC
audio codec relies on SBR technology in achieving good results at 96 kbps and
lower.