Shedding light

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TOSLINK is a plastic optical cable that connects the output of a source device, like a CD or DVD player, to a decoding device like a DAC. Of all the connection schemes for digital audio, TOSLINK is the most reviled. It's really gotten a bad rap. Indeed, it is typically the worst sounding of any digital audio connection scheme. It cannot reliably pass anything faster than 96/24 and has a tendency to jitter the digital audio. From the looks of this post you'd think I would do my best to steer you away from even thinking about TOSLINK. And yetI am not sure that's where I am going. If I were to set out with a clean slate to design a digital interconnect my first thought would be optical, not the better sounding coaxial cable we all like. It is well known that part of the problem with digital transmission systems (seeyesterday's post) isn't confined to the DAC itself. No, in fact, you could build a perfect device that paid no attention whatsoever to the interconnection between the CD transport and DAC and still hear changes between different mediums (like coax or balanced). Why? Because the source device performance can be skewed by merely connecting the two devices together. In fact, tying just the grounds together of two digital audio products can change the performance of both. But connect the two optically and the grounds never touch. The one device doesn't know or care it's connected to the other. It's perfect. Except it's not. The plastic fibers used to transfer light in the TOSLINK cable hold back the speed at which the light can change between light and dark (making the 1s and 0s). If you use quartz (glass) instead of plastic, you get really excellent performance, but speeds are still limited. So why would I have chosen optical for my mythical new digital interconnect design? Consider that most of the world's high speed network data travels on fiber optic cables and has bandwidth that blows the doors off anything we could ever hope for in audio. TOSLINK in theory. Not in practice. TOSLINK is an acronym for Toshiba Link and was designed and popularized by the company that it's named after. But Toshiba is in the process of abandoning the much maligned cable and before long, there won't be anything called TOSLINK. So if the world's data increasingly travels on fiber optics and the speed (bandwidth) of those data exceed the demands of even the highest sample rate audio imaginable, why is Toshiba dropping TOSLINK and why should we care? Let's chat again tomorrow.
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Paul McGowan

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