Antelope Audio Isochrone OCX

For the digital audio studio, there can be no better friend than a stable master clock source. The master clock controls the accuracy of the sample frequency in a digital audio converter. While audio interfaces do have an on-board clock, often these clocks either are not as stable as most of us would like, or they don’t have sufficient distribution capabilities to clock all of the interfaces many studios now require. There are essentially three things a high quality master clock like the Isochrone OCX will do for you. It will improve the audio quality of the A/D or D/A conversion by reducing jitter (irregular timing from sample to sample). It will clock multiple digital devices to reduce or eliminate pops and clicks when doing digital transfers or when two or more digital devices are running simultaneously in a system. Finally, like most master clocks, it allows for distribution of master clock to several devices at once.

Before I dive into examples of how the Isochrone performed in our tests, let’s talk a little about the history that went into making the Isochrone OCX master clock. Back in the mid-90’s (a long time ago in the history of digital audio), Igor Levin founded the company, Aardvark Audio, and released the Aardsync, which turned heads by improving the sound quality and performance of digital audio converters. At that time most of us had no idea what that video bnc connector was doing on our audio interfaces to begin with!

About 5 years ago, he improved on his ground-breaking clock technology with the AardsyncII master clock, which further advanced the quality of clocks for a new breed of audio converters running at ever increasing sample frequencies. In fact, the AardsyncII (and more recently, Apogee’s Big Ben) took the quality of digital clocks to such a high level that the common belief has been that clocking can’t be improved much beyond where it is now. “Wrong!” says Igor Levin (today with Antelope Audio). The basis of clock designs is a small piece of quartz crystal. This piece of crystal, being a natural element, is subject to changes in environmental conditions. As the quartz heats up it changes shape and size and resonates at a different frequency, making it unstable. Igor’s solution, short of using an atomic clock (the most stable clock on the planet), is to control the temperature using an Oven Controlled Discrete Transistor Crystal Oscillator, which Antelope Audio claims is 100 times more stable than the best clocks on the market, until now! The crystal in the Isochrone OCX is heated to a point somewhere above that of the unit and that temperature is maintained consistently by the oven, making it no longer susceptible to the fluctuations inherent inside of a power supply driven electrical device.

The Isochrone reduces jitter by using a discrete transistor design, which is something unique to OCX. Think of it in the way of mic preamps: IC mic pres are noisier than discrete pres, in the clocking world that noise translates to jitter. So by using a discrete, low noise transistor oscillator, the isochrone is able to achieve ultra-low jitter. By the way, the Isochrone OCX does have an atomic clock input, for most the demanding applications. Doing high quality digital audio is indeed a science and for those of you who want to know more about it, I highly recommend the book Digital Audio Explained, by my friend Nika Aldrich, available at cadenzarecording.com.

The converters I use are the RME Fireface800 and the Digidesign 96IO and I have been quite satisfied with both of them. I use a pair of Sennheiser HD280Pro headphones much of the time in my 1 bedroom LA apartment and when I do “crank it up” a bit, it’s on Dynaudio BM5A monitors. The main reason I didn’t expect to hear a great improvement when adding a master clock to the setup is that I am mostly using virtual instruments on my projects at home and the only “recording” I do is vocal work and the occasional guitar into an Avalon U5 active DI. When I started to A/B between the internal clock and the Isochrone OSX, I was therefore surprised to hear my software synths and Giga Studio instruments tighten up and improve the way they did. The improvement I heard was an increased clarity and definition of the sound of every virtual instrument I use, Cakewalk’s Z3TA (my new favorite), Giga Studio, Sampletank and Stylus RMX to name a few.

They all sounded as if a veil was removed and the imaging was much more in phase. The difference is subtle, depending on the circumstances. . I say this as, other than the need to clock multiple digital converters, improved audio quality is usually the main reason to purchase an Isochrone or any professional master clock. Since the clocks in most of our digital interfaces are already better than those in most consumer CD players, ultimately the listener may never know the difference. If, however, the improved audio makes you excited enough to work in the studio longer or adjust a mix to make it a touch better then it seems like the investment is well worth it. If you doubt it and wonder at all then I suggest you spring for one and let your ears be the judge. I have never had a customer tell me a master clock didn’t improve an audio interface, so most of us do hear the difference. If your interface has a BNC input (or a digital input, for that matter) then you can clock it. I did this with the M-Audio Firewire Audiophile and the difference was much more stark than on my interfaces in my setup at home, so the more refined the setup, the more obvious the differences. All this testing made me curious what sort of differences our Isochrone customers are having with their setups, so we asked Keith Hersch what he thought of his.

Keith J. Hersch is a film composer in Los Angeles. His setup includes (1) Behringer ADA8000, (2) RME HDSP9652s, (5) Terratec EWS88D cards with Clockworks word clock daughter cards on (5) PCs: one running GigaStudio 2.54 and Kontakt 2 on the remaining four machines. After Keith connected the Isochrone OCX to all 8 of his devices via word clock, maxing out the Isochrones 8 BNC outputs, he noticed an immediate improvement in both audio quality and stability. He noted specifically the improvement in the "focusing of the high frequency information and an improved depth of field". His work has been positively affected thanks to the improved reliability. He previously had cards switching sampling frequencies on their own, other than what they were set to, due to unstable word clock distribution. He also doesn't lose all of his systems in the event of a system crash on his main machine, nor does he have to start up his machines in a specific sequential order, as in the past. Keith has gained a half hour to an hour in productivity each day and he also says he's writing more, since his sound libraries have much better fidelity. Even his East West Symphonic Gold bundle and VSL First Edition libraries, both of which are 16 bit, sound much better now with the Isochrone as the master clock source.

The Isochrone OCX supports sampling rates up to 192 kHz. It has 8 wordclock outputs and outputs 7 and 8 can be set to multiples of the clock rate, up to 256x super clock. There are also 2 AES/EBU outs, as well as 2 S/PDIF outs, as well as an atomic clock input and thru. If you need more than that, Antelope Audio also make the Isochrone DA and if you’re in need of a video clock input, they will soon be shipping the Isochrone OCX-V model.

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