Joint-stereo is the default mode for stereo files with VBR when -V is more than 4 or fixed bit rates of 160kbs or less. At higher fixed bit rates or higher VBR settings, the default is stereo. Stereo: In this mode, the encoder makes no use of potentially existing correlations between the two input channels. It can, however, negotiate the bit demand between both channel, i.e. give one channel more bits if the other contains silence or needs less bits because of a lower complexity. Joint stereo: In this mode, the encoder will make use of a correlation between both channels. The signal will be matrixed into a sum (?mid?), computed by L+R, and difference (?side?) signal, computed by L-R, and more bits are allocated to the mid channel. This will effectively increase the bandwidth if the signal does not have too much stereo separation, thus giving a significant gain in encoding quality. Using mid/side stereo inappropriately can result in audible compression artifacts. To much switching between mid/side and regular stereo can also sound bad. To determine when to switch to mid/side stereo, LAME uses a much more sophisticated algorithm than that described in the ISO documentation, and thus is safe to use in joint stereo mode. Dual channels: In this mode, the 2 channels will be totally independently encoded. Each channel will have exactly half of the bit rate. This mode is designed for applications like dual languages encoding (ex: English in one channel and French in the other). Using this encoding mode for regular stereo files will result in a lower quality encoding. Mono: The input will be encoded as a mono signal. If it was a stereo signal, it will be downsampled to mono. The downmix is calculated as the sum of the left and right channel, attenuated by 6 dB.

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