国际标准：MPEG-Ⅱ采用了分层的编码体系，提供了4种技术，它们是(56)。数字音频采样和量化过程所用的主要硬件是(57)。

(69)

(68)

(66)

(67)

(64)

(63)

In　information　theory,　"information"　is　regarded　as　knowledge　which　reduces　or　removes(71)　about　the　occurrence　of　a　specific　event　from　a　given　set　of　possible　events.　The　concept　"event"　is　to　be　understood　as　used　in　the　theory　of　probability.　For　instance,　an　event　may　be　the　occurrence　of　a(72) character　or　word　in　a　given　message　or　in　a　given　position　of　a　message.In　communication　theory,　channel　is　defined　as　that　part　of　a　communication　system　that　connects　the　message　source　with　the　message　sink.　An　encoder　may　be　inserted　between　the　message　source　and　the　input　to　the　channel,　and　a(73) between　the　output　of　the　channel　and　the　message　sink.　Generally,　these　two　units　are　not　considered　as　being　parts　of　the　channel.　In　certain　cases,　however,　they　may　be　considered　as　pans　of　the　message　source　and　message　sink,(74) In　information　theory(75) to　Shannon,　the　channel　can　be　characterized　by　the　set　of　conditional　probabilities　of　occurrence　of　all　the　messages　received　at　the　message　sink　when　a　given　message　emanates　from　the　message　source.

(62)

(61)

(58)