 If the difference between left and right is large, standard (discrete, left/right) stereo encoding may be preferred, as mid/side joint stereo will not provide any benefits.An MP3 encoder can switch between m/s stereo and full stereo on a frame-by-frame basis.Unlike Layers I and II, MP3 uses variable-length Huffman coding (after perceptual) to further reduce the bitrate, without any further quality loss.