Clocking Apogees to HD 192 dilemma!!

[DrC:drive]

Having read Bob Katz book - Mastering Audio, I was impressed by his argument that AD and DA convertors sound best when their Internal clocks are used rather than Ext word clock, as the intrinsic clock jitter of an AD convertor will always be better than the best Ext WC due to the limitations of PLL circuits. Thus all the talk of Big Ben improving the sound is rubbish, because the intrinsic clock on my Apogee SE 8000 is going to have less jitter than the ultra low jitter Big Ben once it has interacted with the PLL in the Apogee. This can be proved measuring jitter with an oscilloscope. Hence I now use my two Apogee SE 8000 on internal clock when tracking into PT. These go via LEgacy port on 192. Now here is my dilemma... I have found that I can leave both units on internal clock, without syncing to each other and not asking the HD192 to slave to the incoming digital signal. This does not produce any problems and the Apogees sound good.The HD 192 is on its internal clock, which is actually best for the DA which i am monitoring from. Is this right?? The theory should be that the HD192 should need to clock to the incoming signal, The units have the AMBUS cards in that allow the Apogees to be seen as 888/24s. I have found that this works well, and have disposed of all my clocking cables,. Can anyone explain to me why this is working?? It certainly sounds better to have the Apogees on internal clock


James Cullen

[thephatboi]

HI, I would be very interested to know if this is true about the PLL (what does that stand for?) negating the benefits of a a better external clock. There may be a point of diminishing returns but I have clocked 888s to my Trak 2 apogee and the 888s sound better to me with the apogee clock, perhaps this is because they were so bad to begin with:) But with the 192 it is not so bad to begin with....? Would love to hear some mastering guy's take on this... thanks!

[DrC:drive]

PLL stands for Phase Locked loop, these circuits are notoriously tricky to get right and in the very best designed convertors, and have had considerable man-hours spent on their development. 888's or 666's as Fletcher calls them, are said to have a poor clock and the internal clock on the 192 is very good. It may be that your Apogee clock is improving the jitter in the 888 via its PLL.

James

[Matt_G]

HI, I would be very interested to know if this is true about the PLL (what does that stand for?) negating the benefits of a a better external clock. There may be a point of diminishing returns but I have clocked 888s to my Trak 2 apogee and the 888s sound better to me with the apogee clock, perhaps this is because they were so bad to begin with:) But with the 192 it is not so bad to begin with....? Would love to hear some mastering guy's take on this... thanks!

Yes Bob K & I have discussed this on the mastering web board & we concluded that in the case of the Digidesign interfaces there is an exception to the rule, especially with the older 888's there is a clear advantage in using high quality external clocks with these interfaces and to a certain extent the 192 interfaces. The problem with the 888's being a poor quality clock where the jitter is very bad. As mentioned, it is not as bad in the newer HD interfaces, but the clock on these while good isn't brilliant & to my ear still sounds slightly better clocked externally from my Cranesong HEDD.

Remember while recording you should in most cases (except 888's) be clocking to whatever is doing your A/D conversion for the best results. I assume if you have apogee converters then you would be using these for your A/D, so make your apogee the master clock. If you use 888's for the A/D then having your clock set to external (apogee as master) you may find this does improve the A/D from the 888. If the clock of the 888 was designed properly this wouldn't be the case. So with other interfaces that are designed well external clocking wouldn't help. Of course clocking externally for playback however does not have any immediate benefits apart from what you may hear through your monitors, it will not process the audio inside your DAW unless you do an outside conversion D/A->A/D in which case the audio would be processed through the master clock.

Anyway hope this helps & doesn't confuse you further.