Thanks Martin for your guidelines cause this is a new point for me
assuming NB clocks are good or very good, and my amr dac unable to have an external sync, i went on the amr website and found this text about clocking:
It seems they have a special solution to adress the point
can you tell me your opinion about ?
if positive, i will conclude the best solution is to stay without clock
Global Master Timing®/Intelligent Memory System®
Before the arrival of the DP-777, the issue of solving jitter introduced via SPDIF using a Phase Locked Loop (PLL) Clock recovery was seen as sufficient. However, this analogue “solution” to a digital problem is woefully inadequate yet is not even commonplace.
AMR’s Global Master Timing (GMT)/Intelligent Memory System (IMS) represent a total “out of the box” systematic digital solution that solves the digital SPDIF jitter issue once and for all. The Intelligent Memory System holds a large number of complete audio samples, so it may completely absorb a large amount of variation (jitter and drift) in the incoming signal, while still sending out data at a fixed and precise clock rate, regardless of variations in the incoming clock.
Central to the GMT clock system is an ultra-low jitter, quartz-driven clock system capable of producing over 28 million different frequencies. When engaged, the GMT system intelligently and dynamically controls the clock that drives the DAC chips and takes the data out of the memory buffer. The GMT Clock is set to precisely match the principal frequency of the incoming clock with a precision of better than 0.001Hz. Hence, if the frequency shifts from 192,000.002Hz to 192,000.003Hz over a period of minutes (drift) which is the minimum to be meaningful, the GMT clock will intelligently and precisely track the change.
Once the GMT clock has correctly calculated the incoming clock, the rate of updating the DAC’s clock with the minimal 0.001Hz step (~0.004ppm accuracy) step is at most, once every few minutes or less. As a result, the DAC clock is completely decoupled from the source and completely stable.
With the GMT clock that drives the DAC Chips and to clock the data out of the memory buffer at the same exact frequency as the incoming clock, there is nil jitter in the source clock, as there is no physical PLL link between the source clock and the clock driving the DAC Chips.
The GMT System is not a secondary PLL as used in some cases and some DACs since the late 1990’s, but an entirely new concept. Instead, GMT is a system that will completely block jitter and only react to compensate any slow drift in the clock source or to adapt to a change in sample rate.
The GMT Zero Jitter mode is available for all digital inputs including the USB input and is the new clock standard reference for the digital audio world.