信息科学与电子工程专业英语lecture10.pptVIP

* 9 The set of exponents is encoded into a coarse representation of the signal spectrum which is referred to as the spectral envelope. This spectral envelope is used by the core bit allocation routine which determines how many bits to use to encode each individual mantissa. 指数集编码为信号频谱的粗放表示形式，称为频谱包络。频谱包络用于核心比特分配例程以确定对每一尾数编码时所需要的比特数。 * 9 The spectral envelope and the coarsely quantized mantissas for 6 audio blocks (1536 audio samples) are formatted into an AC-3 frame. The AC-3 bit stream is a sequence of AC-3 frames. 将6个音频信号块（1536个样本）的频谱包络和粗量化尾数格式化，组成一帧AC-3数据。AC-3比特流就是一系列的AC-3帧。 * 10 The actual AC-3 encoder is more complex than indicated in Figure 10.2. The following functions not shown above are also included: ? A frame header is attached which contains information (bit- rate, sample rate, number of encoded channels, etc.) required to synchronize to and decode the encoded bit stream.4 实际的AC-3编码器比图10.2更复杂，还包括以下未出现在图中的功能。 1．在每一帧前面加上帧头，其中包含与编码比特流实现同步并将它解码所需的信息，如比特率、采样频率、编码声道数等。 * 10 ? Error detection codes are inserted in order to allow the decoder to verify that a received frame of data is error free. ? The analysis filter bank spectral resolution may be dynamically altered so as to better match the time/frequency characteristic of each audio block.5 ? The spectral envelope may be encoded with variable time/frequency resolution. 2．插入检错码以使解码器确认接收到的数据帧中没有误码。 3．分析滤波器组的频谱分辨率可以动态地改变以便更好地匹配每一音频信号块的时频特性。 4．可以用不同的时间/频率分辨率对频谱包络编码。 * 10 ? A more complex bit allocation may be performed, and parameters of the core bit allocation routine modified so as to produce a more optimum bit allocation. ? The channels may be coupled together at high frequencies in order to achieve higher coding gain for operation at lower bit-rates. 5．可以进行更复杂的比特分配，可以修改核心比特分配例程的参数以生成更优的比特分配。 6．可在高频端将各通道相互耦合以实现低比特流工作时更高的编码增益。 * 10 ? In the two-channel mode a rematrixing process may be selectively performed in order to provide additional coding gain, and to allow improved results to be obtained in the even