Both coax and I2S carry the same bits from a streamer to a DAC. What makes them sound different is what happens to the clock along the way.
A standard coaxial S/PDIF connection (including AES/EBU via XLR) sends the digital audio and its timing information down a single wire, wrapped together into one composite signal. At the receiving end, the DAC has to look at that signal, recover the clock from it, and use the recovered clock to time the conversion of samples back into analog. That recovery process is where jitter creeps in — small timing variations that don't corrupt the bits themselves but do smear the moment each sample gets converted. Good DACs work hard to defeat this with reclocking, buffering, and asynchronous sample rate conversion, and a well-designed coax link sounds very good. But the fundamental architecture is: send everything down one wire and let the DAC sort it out.
I2S is a different arrangement. Originally an internal chip-to-chip protocol inside DACs, I2S separates the data, the bit clock, the word clock, and — critically — the master clock onto their own dedicated lines. Nothing has to be recovered because nothing has been combined in the first place. When a streamer like the AirLens is designed to output I2S, it hands the DAC a clean, unmuxed set of signals with the master clock ready to use.
That architectural difference matters more than it sounds like it should. I2S is remarkably better sounding than S/PDIF — not by a hair, but by a margin most listeners hear immediately when they compare the two in the same system. The reason is exactly what I described: reconstructing a clock from a multiplexed serial stream is where jitter is born, and jitter is one of the loudest low-level distortions in digital audio.
I2S doesn't have to reconstruct anything. The clock, the data, and the framing all arrive on their own wires, and the DAC uses them as-is.
What's the history? Well, certainly, for many years, TOSLINK and coax were the accepted standards until our friend and (now) mentor and team member, engineer, Doug Goldberg brought I2S out of the chassis and into consumer audio while at Audio Alchemy.
Our chief engineer, Bob Stadtherr, established I2S as a modern HiFi standard, and we now publish the protocol openly so any manufacturer who wants to adopt it can. Many already have. The goal isn't for us to own I2S — it's for the industry to move past S/PDIF.
Same bits.
Different journey.
Better sound.
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