Antelope Audio : Critical aspects of high end audio converter and clock design

March 31, 2012
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TECHNOLOGY DESIGN

Where are we with jitter?

“Jitter is another very complicated and controversial topic. Again I do not believe in a simple dictum, ‘the less the better’. I believe jitter can be used creatively like dither – which on the face of it is noise. I explain my philosophy in one video posted on Youtube .  But shaping jitter, something we are doing in our products, is a very complex thing. So if the designer is not versed in the intricacies of jitter, he/she is better off just reducing it as much as they can. Killing the jitter at least allows you to start with a clean slate.”

Are there particular issues in getting digital audio in/out of PCs/MACs successfully? Pros and cons of USB/Firewire/MADI/others?

“We do not see an issue with getting digital audio in/out of either PC or MAC. Our custom-designed USB chip gives us the performance to stream a 384 kHz signal. When it comes to connecting with computers I think USB 2.0 and soon 3.0 is the way to go. Firewire is a dying standard largely replaced by USB. Madi is an aging standard with limited performance, most appropriate for long cable runs. In my view the USB 3.0 has a chance to become the next ubiquitous standard as Thunderbolt is proprietary to Aptel (Apple/Intel) and won’t be universally adopted on Windows or ARM-based mobile devices.”

What should a user be aware of when connecting hi end converters into their recording set up, assuming they have a variety of digital audio equipment?

“When connecting the converters it is best to use balanced audio connections. This aids greatly in preventing ground loop artifacts. The next thing to consider is clocking. It’s best to use one central master clock generator and provide individual Word Clock connections for each device.”

Antelope Eclipse 384 A/D & D/A Converter, Master Clock and Monitoring Controller

Are issues of synchronous/asynchronous operation still relevant today?

“For USB connections one should avoid adoptive mode. The synchronous or asynchronous modes achieve much lower jitter. Many converters are still running adoptive modes. Others are heavily promoting async mode. In our designs we can use both async and synch modes, but we found that the most marketed mode (async) does not provide the smoothest user experience and requires propriety drivers on some operating systems. Since we are one of the few that have the hardware capability to use synch mode we utilize it instead of the async in our DACs. The benefits are excellent jitter performance and smooth user experience without custom drivers.”

Do I need a separate master timing clock?

“I would always recommend the use of a separate dedicated master clock. This is the only way one can be sure that the digital devices are perfectly synchronized and the jitter multiplication due to device chaining is avoided.”

How can I reduce jitter?

“As I mentioned, reducing the jitter is jitter 101. You should strive higher to shaping the jitter as is done in our 4th generation jitter management technology. But to reduce the jitter you should use properly constructed short digital cables; AES connection instead of S/PDIF; avoid using Toslink, and finally, use a centralized master clock.”

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