The perceptual model is mainly determining the quality of a given encoder implementation. The output of the perceptual model consists of values for the masking threshold or the allowed noise for each coder partition. If the quantization noise can be kept below the masking threshold, then the compression results should be indistinguishable from the original signal. Joint Stereo Joint stereo coding takes advantage of the fact that both channels of a stereo channel pair contain far the same information. These stereophonic irrelevancies and redundancies are exploited to reduce the total bitrate.
Joint stereo is used in cases where only low bitrates are available but stereo signals are desired.
Quantization and Coding A system of two nested iteration loops is the common solution for quantization and coding in a Layer-3 encoder. Quantization is done via a power-law quantizer. In this way, larger values are automatically coded with less accuracy and some noise shaping is already built into the quantization process. The quantized values are coded by Huffman coding. As a specific method for entropy coding, hufman coding is lossless.