Using following controls you are able to adjust settings for MP3 format.

• "Samplerate" combobox. With it's help you can choose appropriate samplerate of output MP3 file. You can choose from 32000Hz, 44100Hz or 48000Hz (MPEG1 standart sample frequencies)
• "Channels mode" combobox. With it's help you can choose one of next channels modes of encoding:
  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. 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") and difference ("side") signal. For quasi-mono signals, this will give a significant gain in encoding quality. This mode does not destroy phase information like IS stereo that may be used by other encoders and thus can be used to encode DOLBY ProLogic surround signals.
  Dual Channel(Forced Joint Stereo)
  This mode will force MS joint stereo on all frames. It's slightly faster than joint stereo, but it should be used only if you are sure that every frame of the input file has very little stereo separation.
  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.
• "MPEG Quality" combobox. Use it to set encoding quality. High quality encoding is slower but result sounds better, low quality is faster, you can use it to save your time, but result is mediocre. Choose "Voice" quality if you need speech compression.

Variable Bitrate.
You can enable/disable VBR mode by enabling/disabling "Variable Bitrate" checkbox. You can select here appropriate bitrates for encoding (minimum bitrate used for encoding if VBR mode is disabled), and also set VBR quality.