World Broadcasting Unions Digital Radio User Manual - -3.5

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.