A test and measurement instrument includes a pattern detector for detecting a beginning sequence in a signal under test (SUT), and generates a synchronization signal. In response to the synchronization signal, a memory outputs a reference test pattern. A symbol comparator compares the reference test pattern with the SUT. The symbol comparator can produce a symbol error rate. One or more 8b to 10b converters receives the SUT from the input and the digitized data from the memory, and converts the data from an 8b coded format to a 10b coded format. A bit comparator compares the 10b coded reference test pattern with the 10b coded SUT in response to the symbol comparator. The bit comparator is coupled to a bit error counter, which produces a bit error rate independent of any disparity errors that may be present in the incoming digitized data received by the test and measurement instrument.