I have the Rossini DAC and Clock. On my Clock are switch for Dither 1 and 2. Is there a difference is sound quality when they are on or off?
The purpose of the switch is to let you make up your own mind. Only you will know which sounds the best to you or if you can’t hear any difference. There is no “right” answer.
The idea with this function in short is that small dither is inserted to exercise the clocks ccx crystal to make it do fast self corrections to the locked frequency, so it does not slides slight out of sync.
I feel the best performance is to use dither for a short while and then turn it off when you want the best possible timing focus. If you feel that the timing and focus fades away one day, just turn it on for a while.
From a technical point of view dither stress the clock to repeatedly correct so it can wear
slightly faster, and you will get a more clean clock signal with it set to off to my ears, so use it from time to time.
That is my best advice from experience.
I don’t believe thats the case at all.
The Dither in dCS’ clocks do not affect the clock accuracy nor the stability of the (reconstructed) clock signal within the DAC since the Dither is random in nature.
If I’m not mistaken, the Dither is designed to improve the Phase-Lock-Loop’s (PLLs) recovery of the incoming clock signals by forcing the clock signal’s edges out of any “dead-zones” within the PLL’s operating range, thus allowing the PLL to better converge on the clock signal. So, best to leave Dither ON all the time in my opinion.
It has nothing to do with short or longer term clock stability or accuracy; which is what you‘re suggesting.
I’m sure the dCS folks can confirm either way.
I believe that is correct. I remember that explanation from dCS when their first home audio system clock ( the Verona) was released. In those early days I was loaned one for a short period but could not hear a significant difference when it was installed in my ( then) Verdi/Elgar plus/Purcell plus rig. Later I changed my mind and purchased one and have retained a clock in the dCS stacks that I have owned since.
The idea of dithering the clock was ( from memory) suggested to dCS by PhD student who was gaining experience during a summer vacation posting at dCS. This was a new concept and had not existed in the preceding professional system clocks. Hence a switch was provided so that the user may make up his/her mind whether to use it or not. Obviously some users may object to adding a small amount of noise ( dither).
My own experience is that initially I could not even hear the addition of the clock per se! That was a long, long time ago and I could now not happily listen without one ( as I found out back when my old Paganini Clock went back to the factory for upgrading to Clock 2 and I was without one for a couple of weeks).
To me the effect of adding dither is extremely subtle. Of course it does not extend the bass by an octave nor let you know what colour socks the guitar player is wearing It is not an “effect”. That switch provides a still useful option.
This isn’t an easy one to answer without the use of some diagrams I am afraid, but I’ll do my best!
When synchronising two clocks, for example a Rossini Clock and that in a Rossini DAC, a Phase-Locked-Loop (PLL) is used in the DAC. This employs a ‘phase detector’ to essentially match the phase of the incoming master clock signal with the DAC’s internal clock. It tries to get the phase error as low as possible.
Phase detectors work very well when the phase error is quite high (where the two clock signals are a fair bit out of phase), but ironically they lose sensitivity as they get very close to the target phase. This is where the dither comes in: Perhaps counter-intuitively, if you apply very small, random variations in the timing of the clock signal edge when your phase error is very low, it gives the PLL something to latch on to and correct (as it pushes the phase error slightly back into the area where the phase detector can correct well). This dither then filtered out in the PLL before it outputs the final clock signal. In practical listening this is a good trade-off and actually improves system performance.
In essence, the dither setting on your Rossini Clock keeps your Rossini DAC’s clock very accurate even when it is working in a less sensitive area.