TV Optical Audio with dCS — FAQ's
If your television is connected to a dCS system using optical S/PDIF (TOSLINK), you may occasionally experience clicks, pops, brief dropouts, or loss of lock. This guide explains why that can happen, why another DAC may appear to work without issue, and what it means for your system.
Frequently Asked Questions
Why can a TV’s optical output cause clicks, pops, or brief dropouts?
The optical output on a television is generally treated as a convenience feature. It is designed to work with a broad range of consumer audio equipment, so the timing of the digital signal may not be controlled as tightly as it would be on a dedicated high-end digital source.
If that timing varies too much, the DAC may briefly lose its grip on the incoming signal. That can result in a click, pop, short interruption, or temporary loss of lock.
What is “jitter” in simple terms?
Digital audio relies on very precise timing. “Jitter” is the term used when that timing varies from where it should be. A DAC has to recover a stable clock from the incoming S/PDIF signal before it can reproduce the audio correctly.
Why might another DAC work perfectly with the same television?
Different DACs recover the incoming clock in different ways. Some products are designed to tolerate a wider range of variation in the incoming signal, so they may continue to play even when the source clock is less stable.
That does not necessarily mean one product is working correctly and another is faulty — it can simply mean they have different tolerances for the quality of the incoming digital signal.
Why can a dCS system react differently to an unstable TV output?
dCS systems place a strong emphasis on low-jitter clocking and on rejecting timing errors from the source. The clock-recovery system therefore operates within tighter parameters rather than simply following every variation in the incoming signal.
The benefit is improved rejection of jitter from a good digital source. The trade-off is that an unusually unstable or marginal S/PDIF output can occasionally move outside the range that the receiver can comfortably track.
Does this mean my TV or dCS system is faulty?
Not necessarily. In many cases, this is best understood as a compatibility issue between the stability of the television’s digital output and the tighter clocking requirements of the audio system.
Can a reclocker help?
Sometimes. A reclocker can accept the less-stable digital signal from the television and generate a cleaner, more stable S/PDIF signal for the DAC.
It is not guaranteed to solve every case, and adding another device to the signal path can introduce its own considerations, but it can be effective where the television’s output clock is the underlying cause.