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All information in these pages is copyright (c) 1989-2003 by Roger Nichols. All rights reserved. Permission for personal reference only, and may not be reproduced by any method without written permission.

WORD

By Roger Nichols

As I write this column I am looking down at the Pacific Ocean from 30,000 feet on my way to Japan for a Steely Dan tour. The second leg of the tour will be across the US in June and July, with the third leg following in Europe this September. Maybe they should have called it the Steely Dan "Tripod Tour." Maybe not.

I have figured out the difference between First Class and Business Class. First Class gets warm peanuts and has 96kHz word clock at every seat. Business Class gets cold peanuts and no word clock, only laptop power connectors.

Computer Connections & Rocket Network

More and more hotels are equipping their rooms with Ethernet computer connections to the Internet. Instead of seeing download speeds of 2k to 4k per second, the meter on my browser says 200k per second. I downloaded everything I could lay my hands on just to see how fast it was. I now need a bigger hard disk.

DSL is finally available in my section of Miami. I am putting in two DSL lines with teaming software that will give me 2.5 megabits per second. The advantage of DSL over cable modems is that you can communicate fast in both directions. I always have lots of graphics or audio files to send and receive, so modem speeds just won’t hack it.

What Up Wit DAT

My need for speed comes directly from my introduction to the Rocket Network. Steinberg’s Cubase VST with Rocket Power and Emagic’s Logic Rocket support a new network whereby multiple sessions on computers connected to the Internet can share the same MIDI and audio sample data. In the past there have been schemes that would allow distance collaboration, but they have failed. This is because they tried to collaborate in real time. The laws of time and space sent them packing. Rocket Network is different.

Each participant in a session has all of the audio and MIDI files associated with the session on his local computer. When a new participant joins the session, all of the files are downloaded to his computer. Each musician records his track on his own computer with his own word clock, playing back and recording on his own gear. When he is done with the overdub, the final results are uploaded to the master session computer and then downloaded to additional participants as needed.

As an example, let’s say that I am in Miami and have a song that I want Dean Parks to overdub a guitar on. Dean is in LA. Dean is busy. Dean and I have been talking about "Phoning in your parts" for 20 years. Now we can do it. I start a session with a mix of the track that he is to play on. I log onto the Rocket Network. Dean logs onto the Rocket Network and joins my session. The session is downloaded to his computer. I go about my business working on other stuff while Dean works on his guitar part. When he is done, the final guitar track is uploaded to my session. I play it back on my computer to listen. Great! I never have to look Dean in the face again. It is like e-mail for digital audio. You get to carry on involved conversations without ever hearing the person’s voice.

Remember that this is digital audio. The guitar part I am playing back is a clone of what was recorded 3000 miles away. Think of it. No waiting for FedEx, no dual machine lockups over ISDN lines, no expensive plane tickets and hotels and escort services for out of town musicians, no "I didn’t bring that guitar" excuses, just the ability to get the project done with the guys you want at a budget that is affordable.

Try it yourself. I think you’ll like it. Now we just have to get more companies on the bandwagon to support the Rocket network, like maybe Digidesign…. Then Steely Dan can work in New York while I edit and slide tracks around by my pool in Miami. Yeah, that’s the ticket.

At One With Word Clock

I have talked in the past about word clock problems and sync issues, but most of the questions I get on the EQ bulletin board are sync related. So, here comes a little word clock refresher course.

There are two types of synchronization signals; those that provide speed reference, and those that provide position reference. Pilot tone, word clock, bit clock, AES and S/PDIF, Digidesign superclock, tach pulses, bi-phase and video sync provide speed information. This speed information is used to synchronize analog machines, digital machines, video machines and DAWs so that they all run at the same speed. MIDI Time Code, VITC (Vertical Interval Time Code), and burned in time code provide positional reference so you can locate multiple machines to the same point in time. SMPTE time code and ADAT sync provide both speed and position information at the same time. There may be one that I left out, but hey… I am powering down free drinks at 33,000 feet.

When digital audio is transmitted from one device to another it is done serially. That is, the 24 bits sample is taken of an analog signal at one point in time, taken apart into individual bits, sent down the wire one bit after the other, put back together at the other end and then put out as an analog sample equal to the input. AES and S/PDIF signals contain some extra information that tells the receiver where the start and end of each sample is in the stream, so it is called "self clocking." The word clock and bit clock are built into the signal.

In some digital audio interfaces, there is no reference built in, so the reference has to be carried externally. Enter word clock. The word clock signal is just a pulse that announces the start of the sample bits. Without word clock, the receiving device would not know which bit was supposed to be first, and you would hear hissing, tearing garbage. I am sure you are all familiar with that sound. If not, you must still be recording analog.

You Shall Have But One Master

Digital audio must have been around for a long time before it was re-discovered, because even the Bible says there can only be one Master. This proves that Cleanliness in Digital Audio is next to Godliness.

Any time two digital audio devices are connected, one must be the master, and the other one must be the slave. Most of the time this is taken care of automatically. When you switch a DAT machine or a CD recorder to DIGITAL INPUT, it automatically synchronizes to the external digital signal’s clock. Since the clock is built into the AES or S/PDIF or optical or ADAT signals, the user is not aware of the changeover. Digital consoles and DAWs can have other sources besides AES for digital input. Tascam TDIF needs a separate word clock (TDIF-2 includes word clock). SDIF (Sony multi-track format) and Mitsubishi’s ProDigi interface require word clock.

If two digital devices are connected and they are both selected to INTERNAL CLOCK, then the receiving device will not know where the samples begin and we will again get the hairy hash sound we have grown to love so much.

You can never get hurt if you have word clock and AES cables connecting two digital devices. If the digital audio is going through the AES cable or ADAT light pipe, a word clock cable going out of the master into the slave, and you have word clock selected in the slave device, everything will work fine. The word clock signal is lined up with the clock built into the digital audio signal, so both devices should remain happy.

If you have a digital console, DAW, ADATs, DA-78s, and whatever else all connected together remember to have one master, and everything else is a slave. I use the Aardsync box for a master clock and connect it to everything. The clock doesn’t have to loop through all of the slaves. If you are using the Aardsync, you can send it in parallel to all of the devices that accept word clock. There is also an AES sync signal generated in the Aardsync. This can be connected to devices that do not have word clock inputs, but sync to an external AES signal. Once everything is connected properly, you will no longer have that "syncing feeling."

Done For Now

Well, I still have 1,234 hours left in this flight. Maybe I will go ahead and do all of my columns for the rest of the year.