THE JITTER PROBLEM

To grasp how a master clock can result in a drastic improvement in sound quality, we have to understand the “jitter” problem. For example, suppose you have a piece of digital gear with a 44.1kHz sample rate. Essentially, this gear is taking a measurement of the sound’s waveform every 1/44,100th of a second. But with so many samples being taken so often, inevitably a sample ends up being taken either a little too soon, or a little too late. This tiny, yet ultimately noticeable, timing error constitutes “jitter.”

While the jitter is typically in the hundreds of picoseconds to the lower nanoseconds, it will make a noticeable difference in sound quality that’s especially evident in frequencies below 5,000Hz. This is because the timing errors in sampling will result into frequencies generated above and below the frequency being sampled, creating the so-called side bands which we perceive as distortion. Jitter can also “collapse” the stereo image somewhat.

What’s truly disheartening is that every piece of digital equipment in your studio is going to be plagued by jitter. What’s worse is that when using a digital recorder, there’s jitter when running the signal into the computer, as well as back out. Before long these timing errors start to accumulate, and greatly diminish the overall sound quality.

APPLYING THE BIG BEN

Apogee has been widely respected for their C777 clocking technology (a staple of many of their devices, and the heart and soul of the Big Ben). Developed using Direct Digital Synthesis technology (DDS) and DSP-based digital filtering, C777 clocking is considered much more effective than the traditional phase lock loop circuitry (which lacks dynamic adaptability). Bottom line: DDS basically regenerates a stable, low-jitter signal that replaces the original clock signal. It can act as a precision master clock, regenerate its own clock signal, or accept signals from external sources at sample rates of 44.1–192kHz. These sample rates can then be varied (or “VSOed”) by –44/78%, for ±999 cents.

Big Ben accepts the following inputs: two AES (XLR), S/PDIF (RCA), SPDIF or ADAT/Smux (optical), word clock (BNC), and composite video. Big Ben’s outputs consist of two AES, S/PDIF, S/PDIF or ADAT/SMUX (optical), and six word clock outs, four of which transmit regular frequency clocks while the remaining two can also transmit up to 256 multiples of the clock signal. A video sync (re-) generator board is available as an option.

Integrating Big Ben into your studio is fairly simple, as the unit offers warning lights for over- and under-termination in your clock signal chain. (Termination minimizes reflections going back along the clock line, which can be a source of error.) This is incredibly useful during installation, as the indicator lights for each clock out alerted me to whether or not I was terminating in the correct location, and if the line was properly terminated.

Apogee’s SureLock technology also assures that the Big Ben’s outputs will remain stable even in the face of an external clock failure — which is super handy when the odd cable pops out in the middle of a session (this actually happened while I was testing the unit). Another helpful Big Ben feature that will have users wearing out buttons is its ability to convert signals in real time from SPDIF to AES to ADAT (and vice versa) with ease.

CONCLUSIONS

Even at one tenth of a nanosecond, jitter adds up and can quickly become noticeable in your recordings. Big Ben, though not the only solution, is indeed a fine one — and I like the additional real-time format conversion feature. Being able to regenerate external clock signals truly adds to the efficiency of your studio, and the “SureLock” technology means you can rest assured there will be a constant, glitch-free clock at all times.

Centralizing your clocking signals for system configuration changes is now a breeze, and being notified if the clock line isn’t properly terminated makes adding the Big Ben into your chain relatively stress-free. What began as a simple trial run, with the overriding question of “do I really need this,” has ended with Big Ben becoming an integral piece of my rig.

Product Type: Digital word clock.
Target Market: Individuals using multiple pieces of gear with internal word clocks.
Strengths: Exceptional jitter reduction and format conversion/support. Multiple outs. Clock signal maintenance despite input loss. User-friendly installation.
Limitations: None.
Price: $1,495 list
Contact: www.apogeedigital.com