Looking at the AES3/EBU input
AES3/EBU
An external AES3/EBU receiver is used to generate the required DSP input stream. With a digital stream it is impossible to achieve more than 0 Dbfs so this is modelled to be equivalent to +6dbV input, meaning that -6 Dbfs is the nominal level for full modulation.
The asynchronous AES33/EBU receiver details
The DSP for this design (ADSP21161) does not have a EBU-AES3 receiver so an external receptor has to be used. When the combined stereo generator with digital exciter is presented a more modern DSP with a digital receptor is used, thus simplifying the circuitry. An asynchronous digital receiver is required so that the DSP sample rate does not have to be synchronised with the AES3/EBU digital signal clock. If it were the pilot frequency would be dependent on this clock as well. Since the digital source could be with 32k to 192k sampling this is clearly not desirable. The asynchronous digital converts the incoming digital stream into exactly the same data stream as the ADC, so from the point of view of the DSP the source is irrelevent. The receiver choosen is the Cirrus Logic CS8416.
There are two possible inputs. The professional balanced XLR and the consumer SPDIF unbalanced. The input is selected by the DIL switch at power on. The four LED are for the display of the input signal status, audio data detected, synchronisation, error detection. The receiver acts as the master for the data stream to the DSP so synchronising the DSP to sample on the correct flank of the L/R clock. The digital sample value for 0dbFs needs to be known so that this level can be set to be equivalent to a MPX modulation level. In order to be equivalent to the analog stream, this design uses -6dbFs for the full MPX ± 75Khz modulation level.