Bit by Bit – Digital Takes Over

My friend Bonko, the guitarist in a retro-alternative-grunge band, is adamant: "Digital stinks, and analog rules, dude." He covets his tube transistors and even has a collection of vinyl records.

"Analog is, like, the bomb! Check out the difference," he said as he cranked the volume on an ancient Jimi Hendrix album. After about ten seconds, he lifted the needle off the record. "Don’t want to grind it down, man," he said. He then played the same song from a CD.

"Sounds identical to me, Bonko," I quietly ventured.

"Yeah, well you’ve got a tin ear, dude. Too bad!" he retorted.

Bonko has got me thinking. With all the talk about the new world of digital, are we all just falling for marketing hype? Is this just another case of planned obsolescence?

When I get confused about such things, I usually visit my old professor, Dr. Mylar, who practically invented video. I can always count on him to give me a straight answer.

I dropped by his office where he was hunkered over an unsightly pile of books and diagrams.

"Hello, Dr. Mylar! It’s your favorite student with a question!"

Dr. Mylar’s absorbed look cracked into a smile when he saw me. "Only one? You used to be more ambitious."

I told him about Bonko, and then I asked him my question: "What format should I use for shooting, editing and archiving video?"

"Sounds like three questions to me," he said, as he pulled up a chair for me. "But as usual, I’ll cut you some slack."

Shooting Digital Video

"For shooting video, digital is the way to go. The latest machines have resolution superior to anything that came before. The consumer video format, Mini DV, is on a par with Betacam, which is a professional format.

"As I’m sure you remember from your video class, American TVs have 525 horizontal scan lines. That’s the NTSC standard. But what’s more important, are the vertical lines, or dots that you can cram into each horizontal scan line. The DV format (including Mini DV and Digital8 provides up to 500 lines, which is more than twice the resolution of standard VHS," he said.

"When I took classes from you, everything was analog. As I remember, the raster converted light intensity to voltage, which got recorded on the tape. How does digital work?" I asked.

"That’s so easy, even you can understand it. A timer is set to look at, or sample, the video stream 13.5 million times per second. For every sample, it reads the voltage level and converts it to an 8-bit number. That’s the luminance, or intensity. Every fourth count, it also samples the color, or chrominance," Dr. Mylar said.

"How does all that fit on a tape?"

"Good question. That’s one of the major stumbling blocks to digital video. A 500×525 screen with full color requires three-quarters of a million bytes to store it! Multiply that by thirty frames per second and you get about twenty million bytes every second. Without compression, it would take a while to make digital video practical."

"How do you compress a the signal?"

"To answer that, I need to invoke a little mathematics. Are you ready?"

I wasn’t, but I lied. "Sure, go for it."

"A French mathematician named Fourier," he began, "discovered that any signal can be represented as the sum of simple sine waves. This is the basis of the Discrete Cosine Transform, or DCT, which is at the heart of digital compression. It manages to squeeze still pictures into a fraction of their original size," Dr. Mylar explained.

"The DCT splits an image up by frequency components and then tosses out certain ranges. The converted and compacted data is what gets stored on the tape. When the data is fetched off the tape, it gets reconstituted by an inverse transform – similar to the way division can undo multiplication. With the DCT algorithm, the data rate goes down to about 3.5 megabytes per second (MBps). Still hefty, but manageable by current recording technology."

"What if you drop a bit or two?" I asked him.

"That’s another advantage of being digital: you can use error correction. Error correcting codes can fix most localized drop-outs before you ever see them on tape or TV."

"And they digitize the audio too?"

"You bet. Digital video sports a stereo track of 16-bit, 48kHz audio-better than CD quality. There’s also an option to use four sound channels with 12-bits at 32kHz. The quality suffers a bit, but it still beats the heck out of ordinary VHS. Four channels are nice: you can use two for live sound and use the other two to dub in what you want in post production."

"How do they fit all that stuff onto the tape?"

"It’s not easy," he said. "They use tiny recording heads that spin at about 9000rpm. As the head rotates, it lays down 10 diagonal tracks per frame, with each track divided into four blocks." Dr. Mylar reached purposefully through the mess on his desk and retrieved a diagram.

"These machines are miracles of engineering precision and reliability," he said.

"You mentioned four blocks?"

"Right, the two biggest blocks are video and audio. Of those, video is the largest. Then there’s a block called sub-code that has goodies like the date and time, time code and more. The last block is called ITI for Insert and Tracking Information. What this means is that you can do
professional editing with a consumer deck. And, by marking the in and out points, you can capture video clips with amazing ease. The footage can then be read into your computer, with each clip then sorted and dropped into a separate bin, ready to stitch together."

"So, is Bonko wrong about digital?" I finally asked him.

"If he were talking about shooting video, yes, he would be," Dr. Mylar said emphatically. "Digital produces far superior results."

Editing Digital Tape

What Dr. Mylar said was beginning to make sense, and the benefits of digital were starting to take shape. But I wanted to keep the ball rolling so I continued my line of questioning.

"Well, it sounds like digital is obviously better for shooting, but what about editing? Does analog have any advantage there?"

"Actually, as good as digital is for shooting, it’s even better for editing. Remember from your analog classes how the copies got worse each time? Well, digital can be copied with perfect fidelity.

"Oh, yeah. Generation loss was a bear!" I groaned. "You mean digital fixes that?"

"Absolutely. You can duplicate the image over and over and never lose resolution. I’ve made over 40 generations of copies of a digital tape without any noticeable degradation."

"What’s this I hear about FireWire?" I asked.

"FireWire and DV are two entirely separate technologies, but they both work together like magic. FireWire–also called i.LINK or IEEE 1394–is a high-speed video connector."

"What does it look like?"

"It’s a light-weight cable with six wires inside: two apiece for dual bi-directional data and two more for current. You can use one of the bi-directional lines to handle both recording and playback functions, cutting the number of wires in the cable to four. You can send your editing commands on the FireWire cable as the data. All the DV data is available, including subcode and ITI. It all gets saved to your hard disk for frame-accurate editing."

"I guess it’s a good thing computers come with multi-gigabyte drives these days." I pointed out.

"Oh yeah. At 3.5MBps, you’ll fill a gigabyte drive in less than five minutes. Thank goodness the price of drives is going down even as their speed and capacity goes up."

"I’ve heard that FireWire lets you dump data directly to your hard drive."

"That’s right, and a lot of computers come with FireWire pre-installed," Dr. Mylar said. "You can also copy from one camcorder to another with zero loss."

"Do you have any tips for video editing?" I asked.

"Sure. Keep in mind that nothing taxes your computer more than manipulating video. So give it a break: turn off all other programs–even virus-checkers–allowing the computer to devote its cycles to the video task at hand. Make sure you defragment your disk drive before you start. Then you should get good results."

"Do I need an input card?"

"On some computers you will. If you have built-in FireWire, you’re in good shape. Otherwise, there are plenty of cards available for the task. Some digital video cards are smarter than others–they can even rewind the tape to pick up a dropped frame. A big benefit of digital video in the editing room is the ability to composite.

Since a copy is as good as the original, you can pile up layer after layer of video and still output a pristine image. These effects are extremely limited with analog, since the quality diminishes with each layer. In short, Bonko would be wrong about analog when it comes to editing video. Digital is king here, too."

Archiving Digital Video

"OK, so far Bonko’s analog argument hasn’t held up to shooting or editing video. But how about archiving the results? Surely a vinyl record is a great way to store data?" I asked.

"Well, it’s not bad." Dr. Mylar responded patiently. "But think about what Bonko did: he played ten seconds of music and then stopped. He didn’t want to scratch the record. That’s the problem with analog: just playing it back can ruin it. Not so with digital. Here, even if you scratch the tape a bit, error-correcting codes can patch it up. Then you can re-record a precise copy of the original and start from scratch, so to speak. However, digital tape is still tape and no one really knows how long it will last. If you don’t take care of them," he warned, "those videos can be lost forever."

"What can you do about it?"

"Simple: back them up on a regular schedule. That’s what the pros do. Every major TV studio now maintains an archive on digital tape. Every ten years or so, they just pull the tapes and re-record them. The copy is just as good as the original."

"So they’re good for ten years?"

"Well, as long as you take care of them. They may last even longer, since digital signals are inherently more stable than analog, but I wouldn’t push it," he said.

"How do I take care of them, then?"

"The best bet for storage is to keep them in a dry and cool place, of course, far away from any magnetic fields – and that includes big speakers. Many people try to keep them at about 70 degrees Fahrenheit and 50% relative humidity, but that may be tricky in a place like Florida. So just keep them as cool as you can. The most important thing is to check your tapes periodically."

"So, Bonko would be wrong again?"

"Yes. For archiving, nothing beats digital video."

"So what’s Bonko talking about?"

"Well, I suspect that he’s part of a crowd that thinks that digital doesn’t carry enough information to adequately reproduce a good analog recording. And for musical recording, he may have a point. But for video, every single aspect of it is improved by moving to digital. And, unfortunately for Bonko, there’s no turning back."

"I’m not too worried about Bonko," I said, "I’m doing a music video for his group–and it’s all digital. But we’ll just keep that our little secret."

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