Questions and Answer about Clocking

The following questions are answered by DWS (Kent Poon), sound recording engineer who helped design Weiss products.

AD = Analogue to Digital Converter
DA = Digital to Analogue Converter

appleteapot Q: "If DA can do re-clocking and does not require any external clock source, why do we need word clock during AD (recording) stage? "

DWS A: We simply NOT necessary to use word clock. Most mastering engineering uses their ADC internal clock as the master clock, the DAW (digital audio workstation), DAC monitor, recorder are all slaved to the ADC.

appleteapot Q: "Therefore, if the AD clock can in sync with DA clock, AD clock error in theory can sync with DA clock error, then output will be even more accurate? "

DWS A : Okay, the practical way is usually use ADC as mastering clock during capture stage, and DAC as mastering clock during monitor stage. There is hardly a decision on what is more accurate. But you are right if you have a mastering clock that is accurate, then slave both ADC and DAC to the master clock will be a good solution.

appleteapot Q: "offlie upsampling like Izotope or Saracon, is sound card (clock) required?"

DWS A: No, they are offline SRC calculation, clock timing signal only affects real time transfer (AES, SPDIF) etc.

ackcheng Q: "For the best results, the clock at DA should always be the master with everything else slave to it. This is my current setup :) But still, in DAW environment, word clock sync is needed. The question is why Weiss do not allow wordclock in its digital chain?"

DWS A: Right Right Right. DA should be the master with everything else salve to. This is correct. But not many DAC allows to work in this mode because it needs to set a correct sample rate to output. All DACs lock to the incoming clock but not verse vice.

Why DAW needs a word clock snyc? If the Weiss is a AD+DA, then it maybe more reasonable because it is usual case to use ADC as mastering. Weiss ADC2 has wordclock output.

ackcheng Q: "Before I used the master clock, I do can pops and clicks and I thought that was due to sync problem. No more clicks now."

DWS A: Let say you have 2 digital audio card (RME + Lynx) you hook them together with digital AES. Now you playback a file with RME and capture the loop file with lynx, you will have to set the Lynx clock signal as "external AES". You cannot have 2 cards which are both set to "internal" under clocking.

There is always only 1 source (timing) in a system.