Hello all,
I’ve just come across this thread and thought I would add some insight, as I’ve seen this particular S/PDIF issue many times during my previous employment with another high-end audio manufacturer.
Generally speaking, TV manufacturers treat the optical audio output as a convenience feature rather than a precision digital-audio interface. They mostly design these outputs to work reliably with a very wide range of consumer audio products. As a result, the timing of the digital output can be, shall we say, less tightly controlled than we would expect from a dedicated high-end digital source, resulting in relatively high jitter or a clock that wanders more than expected.
A DAC has to recover its clock from the incoming S/PDIF signal using a PLL. Many consumer products use clock-recovery systems that are quite tolerant of variation in the incoming signal and will continue to track it even when the source clock is less than ideal.
Higher-precision audio products (such as ours) place much greater emphasis on rejecting incoming jitter. dCS systems are designed around very low-jitter clocking, so the clock-recovery system operates within tighter parameters rather than simply following variations in the incoming clock.
The advantage is better rejection of jitter from a good digital source. The trade-off is that an unusually unstable or marginal S/PDIF output from a TV can occasionally move outside the range that the receiver can comfortably track, resulting in loss of lock, clicks, pop’s or brief dropouts.
This does not necessarily mean that either product is “faulty”. It is simply an incompatibility between the quality or stability of the TV’s digital output and the tighter clocking requirements of the audio system.
This is also why inserting a reclocker can solve the problem (although it’s not guaranteed and can introduce its own issues). It accepts the less stable signal from the television and generates a cleaner, more stable S/PDIF signal for the DAC.
I will bring this up with our development department to see if we can make accommodations for the wondering clocks of TV’s. I can’t guarantee anything will be introduced, but I will certainly raise the question.
I hope this helps explain what’s happening.
Tom
