Dither : Dither Controls : Bit Resolution Button
 
Bit Resolution Button
Use this pop-up menu to choose one of three possible resolutions for the Dither processing. Set this control to the maximum bit resolution of your destination.
16-bit
Recommended for output to digital devices with a maximum resolution of 16 bits, such as DAT and CD recorders.
18-bit
Recommended for output to digital devices with a maximum resolution of 18 bits.
20-bit
Recommended for output to digital devices that support a full 20-bit recording data path, such the Sony PCM-9000 optical mastering recorder, or the Alesis ADAT XT 20. The 20-bit setting can also be used for output to digital effects devices that support 20-bit input and output, since it provides for a lower noise floor and greater dynamic range when mixing 20-bit signals.