An apparatus and method is disclosed for generating robust ATSC 8-VSB bit streams for transmission by a digital transmitter. The apparatus comprises a Reed Solomon encoder unit that encodes a plurality of bit streams including bits to be encoded in a robust ATSC 8-VSB bit stream and bits to be encoded in a standard ATSC 8-VSB bit stream. The apparatus also comprises a trellis encoder unit comprising a symbol mapper unit in which an output symbol R is forced to a value of minus one minus alpha (-1-) when R equals minus one (-1) and to a value of plus one plus alpha (+1+) when R equals plus one (+1), where the value of alpha () is variable. A control block sets the value of alpha in accordance with the type of bits present within the trellis encoder unit to generate both robust and standard ATSC 8-VSB bit streams.