Isochrone OCX Review by Marcel James

Antelope Audio Isochrone OCX

For the digital audio studio, there can be no better friend than a stable masterclock source. The master clock controls the accuracy of the sample frequencyin 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 theydon’t have sufficient distribution capabilities to clock all of the interfacesmany studios now require. There are essentially three things a high qualitymaster clock like the Isochrone OCX will do for you. It will improve the audioquality of the A/D or D/A conversion by reducing jitter (irregular timing fromsample to sample). It will clock multiple digital devices to reduce or eliminatepops and clicks when doing digital transfers or when two or more digital devicesare running simultaneously in a system. Finally, like most master clocks, itallows for distribution of master clock to several devices at once.

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

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

The Isochrone reduces jitter by using a discrete transistor design, whichis something unique to OCX. Think of it in the way of mic preamps: IC mic presare noisier than discrete pres, in the clocking world that noise translatesto jitter. So by using a discrete, low noise transistor oscillator, the isochroneis able to achieve ultra-low jitter. By the way, the Isochrone OCX does havean atomic clock input, for most the demanding applications. Doing high qualitydigital audio is indeed a science and for those of you who want to know moreabout it, I highly recommend the book Digital Audio Explained, by my friendNika Aldrich, available at cadenzarecording.com.

The converters I use are the RME Fireface800 and the Digidesign 96IO and Ihave been quite satisfied with both of them. I use a pair of Sennheiser HD280Proheadphones much of the time in my 1 bedroom LA apartment and when I do “crankit up” a bit, it’s on Dynaudio BM5A monitors. The main reason Ididn’t expect to hear a great improvement when adding a master clockto the setup is that I am mostly using virtual instruments on my projects athome and the only “recording” I do is vocal work and the occasionalguitar into an Avalon U5 active DI. When I started to A/B between the internalclock and the Isochrone OSX, I was therefore surprised to hear my softwaresynths and Giga Studio instruments tighten up and improve the way they did.The improvement I heard was an increased clarity and definition of the soundof 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 inphase. The difference is subtle, depending on the circumstances. . I say thisas, other than the need to clock multiple digital converters, improved audioquality is usually the main reason to purchase an Isochrone or any professionalmaster clock. Since the clocks in most of our digital interfaces are alreadybetter than those in most consumer CD players, ultimately the listener maynever know the difference. If, however, the improved audio makes you excitedenough to work in the studio longer or adjust a mix to make it a touch betterthen it seems like the investment is well worth it. If you doubt it and wonderat all then I suggest you spring for one and let your ears be the judge. Ihave never had a customer tell me a master clock didn’t improve an audiointerface, so most of us do hear the difference. If your interface has a BNCinput (or a digital input, for that matter) then you can clock it. I did thiswith the M-Audio Firewire Audiophile and the difference was much more starkthan on my interfaces in my setup at home, so the more refined the setup, themore obvious the differences. All this testing made me curious what sort ofdifferences our Isochrone customers are having with their setups, so we askedKeith 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 Clockworksword clock daughter cards on (5) PCs: one running GigaStudio 2.54 and Kontakt2 on the remaining four machines. After Keith connected the Isochrone OCX toall 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. Henoted specifically the improvement in the "focusing of the high frequencyinformation and an improved depth of field". His work has been positivelyaffected thanks to the improved reliability. He previously had cards switchingsampling frequencies on their own, other than what they were set to, due tounstable word clock distribution. He also doesn't lose all of his systems inthe event of a system crash on his main machine, nor does he have to startup his machines in a specific sequential order, as in the past. Keith has gaineda half hour to an hour in productivity each day and he also says he's writingmore, since his sound libraries have much better fidelity. Even his East WestSymphonic Gold bundle and VSL First Edition libraries, both of which are 16bit, 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 wordclockoutputs and outputs 7 and 8 can be set to multiples of the clock rate, up to256x 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, AntelopeAudio also make the Isochrone DA and if you’re in need of a video clockinput, they will soon be shipping the Isochrone OCX-V model.