Please demystify: Wordclock!

[snafu]

Hi everyone,
Lately, I've done some digging in the depths of my DM3200 manual, and found this on page 43:
"The DM-3200 can act as a word sync master or slave
(set up in software—see “Clock setting” on page 44).
The switch allows the OUT to act as a THRU when
the DM-3200 is receiving word sync signals, as well
as enabling and disabling 75Ω termination on the
input."

Well, I never used any digital gadgets, other than the Dm itself. But just recently I got an Focusrite OctoPre, and it gives me 8 inputs/outputs which I can send via Toslink directly to my DAW (as a digital copy, if you will).
The problem is: the Focusrite manual demands 75 Ohms BNC cable, whereas the DM3200 has a switch on the rear with which you can activate/deactivate 75 Ohms. Default seems to be "off". So, well, I guess I should switch it to on, but then again, I couldn't find any digital audio devices that would recommend anything else but 75 Ohms cables, so....maybe I misunderstand something here, but shouldn't the default be "on"?

I am unsure how this all comes together, and if I really want to touch that switch.
I'd like the DM to be the master in ths whole scenario - I think, this makes the most sense, since it is also my audio interface to the digital realm.
Help anyone?

best regards to you guys
snafu

 

[Arjan P]

The DM switch is a 3-position switch, switching between 75Ohm Termination and OFF, and between THRU and OUT. Termination means the word clock chain ends at the DM and you don't need a physical 75Ohm terminator plug (which you would need if the DM is word clock slave and the last in the chain). So that's the center and right switch positions.

You can also see that the left switch position leaves the termination in OFF (upper texts), but switches between OUT and THRU for the OUT/THRU connection (lower texts) so in center position it is OUT and in left position it is in THRU.

In your case, with DM as master, just leave the switch in the center position (no termination and the connector is OUT) and connect a 75Ohm BNC cable to the Focusrite (DM OUT - Focusrite IN). Do check with the Focusrite documentation if you need to do something for the termination there.

 

[snafu]

OMG Arjan, I am a bit embarassed now, 'cause every time I throw in a noob question, you're the first in line! Glad you're helping out!

So, let me see, if I got this straight, because I'm sure I still confuse some things here:
1. This is one switch with three settings for BNC IN and BNC OUT
2. Position left: BNC IN is OFF, while BNC OUT is THRU. OK, so does this mean no signal is coming in (BNC IN), but a clock signal leaves via BNC OUT? I'm trying to think scenario-wise to get a sense of it: so, this would be applicable only to sync another device without wanting to get anything from it in return?
3. Position center: BNC IN is OFF, BNC OUT is OUT. Or as you suggested:

just leave the switch in the center position (no termination and the connector is OUT) and connect a 75Ohm BNC cable to the Focusrite

So there is wordclock to the Focusrite but nothing coming back since BNC IN is OFF. OK...
4. Position right: BNC IN is ON, and so is BNC OUT. OK, I suggest, this is when the DM serves as mere slave?

Anyway - in all of these cases I need a BNC connection from the port that is not "off", correct (i.e. 2 connections in the last scenario)?

OK, but let's say
- the DM3200 is the last device in line and slave. Wouldn't this apply to BNC IN/OUT is ON, right position?

Termination means the word clock chain ends at the DM and you don't need a physical 75Ohm terminator plug (which you would need if the DM is word clock slave and the last in the chain).

So I would need a termination plug here, right? Er, what's a tp anyway?

One final question (for now ;-) ): I heard some people make their DAW master, and all subsequent devices therefore slaves. Any thoughts on that, as to if there is a benefit or completely up to taste on which device acts as master? And which setting (switch-wise) would allow me to make my DAW master?

As always, your help is very much appreciated.
greetings
snafu

 

[snafu]

P.S.: forget about the termination plug; of course I googled it! But - why would I need one? I mean, there is no connection and it seems more like an anti dust cover or something?

 

[-mjk-]

You use the termination plug because you want to prevent reflections of the energy in the cable (which in this case is an RF transmission line). Reflections cause noise, and the terminator's function is to absorb the energy at the end of the line.

 

[snafu]

Thanks mjk, so in essence, whenever I use a BNC, I should (if not needed) terminate the remaining BNC-port with a termination plug?

The more I think about it, the more it makes sense to make my DM the master - it's like my audio card/interface in one go, so I guess it kinda makes sense? On the other hand, everything ends in the PC, so maybe my DAW should be wordclock master.

I guess I am putting too much thought into this. Well, last night it appeared to me, as if using the DAW as wordclock master, might not be too good of a decision, since software changes over time and hence is often optimised for the newest hardware only. Well my studio is build around the DM for the time being, and I stored a second one I got very cheap, just in case, you know...
Anyway: from this perspective the DM seems much more attractive as master, since it's conserved for all eternity in a state as is.

Your suggestions are very welcome.
Have a great day, everyone!

P.S.: still unsure about the questions in my second post

 

[-mjk-]

so in essence, whenever I use a BNC, I should (if not needed) terminate the remaining BNC-port with a termination plug?

It depends on the design of the device. The documentation will tell you if a termination plug is necessary.

 

[cmaffia]

What Arjan said!

 

[Arjan P]

OMG Arjan, I am a bit embarassed now, 'cause every time I throw in a noob question, you're the first in line! Glad you're helping out!

It must be coincidence, but always glad to help!

1. This is one switch with three settings for BNC IN and BNC OUT
2. Position left: BNC IN is OFF, while BNC OUT is THRU. OK, so does this mean no signal is coming in (BNC IN), but a clock signal leaves via BNC OUT? I'm trying to think scenario-wise to get a sense of it: so, this would be applicable only to sync another device without wanting to get anything from it in return?

BNC IN never gets switched off, but the internal 75Ohm termination for IN can be switched ON or OFF. If the DM is clock master, the IN will not be used, but if the DM is slave, the IN will be used ofcourse, and other devices can be connected via THRU and the last one must be terminated to 75Ohms. This site has a nice article about word clock: https://www.musictech.net/tutorials/ten-minute-master-digital-word-clocks/

OK, but let's say
- the DM3200 is the last device in line and slave. Wouldn't this apply to BNC IN/OUT is ON, right position? So I would need a termination plug here, right? Er, what's a tp anyway?

With DM as slave and last in line, you indeed put the switch in the right position, which means you internally connect the 75Ohm terminator that the DM already provides! So no need for a separate termination plug, or.. tp (I guess?)

One final question (for now ;-) ): I heard some people make their DAW master, and all subsequent devices therefore slaves. Any thoughts on that, as to if there is a benefit or completely up to taste on which device acts as master? And which setting (switch-wise) would allow me to make my DAW master?

In my opinion, the master should be the device that takes care of AD-conversion (OR the device with the most stable clock!) and for me that is the DM. I also have a second device as slave for extra analog inputs, in my case an old Presonus DigiMax, which also is clock slave via BNC - there can only be one master...

 

[snafu]

Like so many times before, Arjan: Thanks a lot for your in depth explanation. Very much appreciated! I am in the final steps of finishing my studio, and it was quiet a ride. A lot of technical details came just the last minute (my music pc being too old, had to be replaced, the need for an extra mic pre-amp (which then offered more flexibility, but only with toslink connection) and so forth). So: all in all this case is closed.
I know, I said this many times before, but...: I am amazed at how much you will find about the DM-series when you really dig into it. I can't believe they sold it for 2.5k Euros back in the day, where other mixers with the same backpack of flexibility and quality almost cost double or thrice! For all it is, the DM is killer, and as I said, I was desperate enough to buy a second unit, when I had the chance to get my hands on one for less than 700 Euros. It's hilarious, when you try to wrap your head around the sheer possibilities this piece of tech offers.
Cheers guys, have great rest of the week!
snafu

 

[snafu]

OK, OK, OK - this is really the last one:
in the manual it says, each ADAT port can handle eight channels (inputs AND outpust) @ 44.1kHz/48kHz sampling rate (higher rates reduce the overall amount of channels).
So, at the same rate, the Scarlett also sends eight channels I/O. Effectively, I would just need one Toslink cable, if I don't touch the samplerate. Could the other port (at the TAscam side) therefore be used for another device (given, I prolong my wordclock chain...)?

 

[skier]

Hey Sanfu, I’m just going to throw in my 2 cents here for consideration.

FWIW, I always use the input device with the best internal clock as the master. And similarly, I always hope that the device where the A/D conversion will take place will have that best clock. Here’s my reason: The A/D converter is the place where you truly want the most consistent, accurate clock with minimal variation. That’s because this is the place that the digital signal is created and you want it to be as accurate a digital representation as possible of your analog input of a great performance. If that is accomplished, you could later have a problem with poor D/A conversion if that device doesn’t sync well with the master, or if the master clock circuitry develops problems, or if the clock sync cabling contributes jitter and/or other electrical noise to one or more slave clocks — but so what? The original digital signal was cleanly and precisely encoded with a good clock, so to get a great analog signal back, all you need do is replace the bad D/A converter or the bad master clock or bad cabling with a good replacement and VOILA!!! HOWEVER, if the original conversion wasn’t good, neither will be the created digital signal no matter how good the D/A converter or the clock signal it receives, so there will be no way to get back that great performance. Therefore, the most important point I want to make is to make sure you get a good A/D conversion in the first place, and that requires a good clock timing a good A/D converter.

Generally, in a small or even medium size setup, you can use a good mic pre’s internal clock as the master — even better if that device has a crystal-controlled oven inside for maximum clock stability — the very best (read: EXPENSIVE) devices do. In my case, I use my Focusrite pre-amp’s internal clock as the master and the DM and every other piece of gear is a slave. I will admit that the DM appears to have a good clock and good pre-amps, but I feel the Focusrite is as good or better, so I sleep better using it as the master (maybe I'm wrong ). If I need to record an entire band, then I’m going to also use the DM’s pre-amps and its clock is slaved to the Focusrite; but most of the time, my studio is for my own use to build a song of my composition/playing and/or some friends and me, and we usually can do that with 8 or fewer inputs unless we’re including drums.

Now, in a large studio setup, there are just too many good pre-amps and other devices where A/D conversion takes place, so my recommended approach isn’t practical. These studios usually compensate by employing an expensive, high-grade, external master clock with an internal crystal oven feeding high-quality Word Clock sync signal to all slaves in that studio with high-quality clock cabling as short as possible. And most, if not all, of the devices that are slaved are really high-grade equipment in such a studio. That’s the most you can do to try to get the highest quality A/D conversions on a large number of tracks recorded at the same time.

I hope this helps and isn’t confusing. If I did a bad job explaining, let me know and I’ll try to do better.

 

[Arjan P]

Effectively, I would just need one Toslink cable, if I don't touch the samplerate. Could the other port (at the TAscam side) therefore be used for another device (given, I prolong my wordclock chain...)?

The two ADAT lightpipe (TOSlink) connections are one for input and one for output, so feeding ADAT into the DM3200 is limited to the 8 channels you already use. Wordclock is irrelevant here, since the audio signal is already digital - see skier's explanation above.

 

[snafu]

Thank you, skier, that's some food for thought. OK, so in essence it's like "make the device with the best clock your master". And your input about conversion do digital, and therefore chose the source of conversion as master also makes sense.

Although here's my addendum:
If both devices (DM and OctoPre) were equally good (A/D - D/A-wise) your argument would opt for the preamp as wordclock master. I think, since the DM is the audio interface for the whole studio (at least in my case), it wouldn't be a bad idea to have the audio card be the master.

Did you ever have the chance to do a comparison (DM as master vs Focusrite as master)? Unfortunately - in my case - I must make a final decision; if I'm done with all the wiring, the DM will be embedded in my workspace, and for any changes really, really hard to come by.

The image I attached may illustrate my case.

 

[snafu]

Sorry, something went wrong - I can't fix it, so here we go:
image

 

[skier]

If you decide to use the DM’s clock as the master, you should be fine. And no, I never did actually hook up a scope and look at the clock signals of each, mainly because I feel you should use the clock in your input device to get the best conversion. No matter whether using an external clock or the internal clock of a device, every slave will receive a degraded time signal because of the external cabling needed to connect sync among the devices, the master to all the slaves. When using the internal clock of the device performing A/D, the clock paths are extremely short and pick up far less noise and jitter. But cables are usually at least one meter or more long, plus they have far more capacitance than short traces on a PC board. That capacitance begins the round-over of the sharp corners of square waves which are the actual clock sync pulses. If you use the DM’s clock as the master, you’ve got a good clock with 16 good pre-amps; that’s why I firmly believe you’ll be fine. In my case, I just like my Focusrite and its features as the pre-amp and A/D converter, so its internal clock is the logical choice and likely provides the most accurate conversion.

To add to Arjan’s response: ADAT includes clock information — it’s embedded in the digital data signal. The same is true for AES/EBU (AES3), TDIF and S/PDIF. Word clock is also very important in the video world for syncing sound to pic and you’ll usually find an external master clock in those applications.

 

[snafu]

Thank you skier, thank you Arjan: I still try to wrap my head around this, and it's big chunk of info to swallow here (at least for me). Thought I had it, but now I completely lost it.

So, now I don't need a BNC-cable at all? At least the german manual reads as if I need BNC to play the ADAT game...well, you could read it otherwise, but if look at the english manual it doesn't help me either to fully understand.

More confusing so, the Focusrite manual shows more or less my intended use case but both ADAT ports on the rear of the OctoPre get connected to ADAT inputs of two other audio devices. But I thought one is In, the other Out, so how can they both be connected to two seperate inputs?

I would like to just add an image here, but I can't upload files. Seems I need some special permission? Sorry, for that - but I can upload the pdf manual of the OctoPre; on page 12 / scenario 5 is what I mean.

To summarize: I'd like to connect the OctoPre to the DM, so that I can record whatever signal is at channels 1-8 of the OctoPre directly into my DAW digitally. Oh, and after all, now I am not sure: does it mean, I can send up to eight channels back (from the DAW) to the outputs of the OctoPre? This would be hilarious - and...weird, for the manual states that the OctoPre outputs are always in parallel to it's inputs, so...

I'll chime in tomorrow again. Good night / good day
greetings
snafu

 

[skier]

Try this:

1. Feed voice/instrument signals into the OctoPre. If the OctoPre's output is going to another device as you mentioned, that's likely not the best way to connect it. Instead, use the DM as the central device to connect everything - it's essentially a digital rack. So, the ADAT output of the OctoPre will go to an ADAT input on the DM. Be sure to set the same sample rate on both.

2. Connect a Word Clock cable from the Word Out port on the DM to the Word In port on the OctoPre.

3. Set the Sync setting on the front of the OctoPre to Word (not Internal).

4. Set the Word Clock setting on the DM to Master or Internal (I don’t remember what Tascam calls the setting, but it should be one of those).

5. Connect a Toslink cable from the ADAT Out on the DM to the ADAT In port of whatever device you did have the OctoPre sending data to before starting this hookup (presuming you still want those signals to go to that device).

6. On the DM Routing screens, set the signal(s) you want going to that other device to go out the DM’s Out ADAT port.

I may have missed something because I’m writing this quickly, but the foregoing should make clear the general idea of how you can route digital audio and set clock settings. You may have to read the pertinent topics in the OctoPre and DM manuals to make those settings, but this should give you the general idea.


Good Luck!

 

[snafu]

Thanks, skier! Your explanation should help me to get this thing done. I hope, I was not overcomplicting things - if you never did get in thouch with those things, the manuals don't help so much these days (or maybe it's just me becoming senile^^).

Anyway: went over to thomann this morning, got me a pair of toslink cables, as well as a BNC. I will first test a small setup (DM connected to OctoPre), and see, if there's any difference depending on who's master.

Thank you very much, guys - I'll report back soon.
best regards
snafu

 

[skier]

Snafu, I meant to make more clear with my last post that, I don't know whether or not you just have the ADAT input and output that comes with the DM, or if you also have additional ADAT ports with an expansion module. If the former, then there's no issue. But if the latter, make sure that you assign the input and output ports to which you've connected the OctoPre. While I'm sure you already know this, it's easy to make a mistake with all this and I've sometimes assigned an incorrect port when I've had multiple choices. Then I've had to spend a few minutes (or much more) trying to figure out why I'm not getting any sound.