Why isn’t digital audio “just ones and zeroes”?

  • Connections. Between streamer and DAC we have choices: The ubiquity of consumer-grade PCs and SBCs has seen USB rise to the top of the popularity pile but network streamer manufacturers often add various combinations of the three S/PDIF outputs to broaden their device’s deployment possibilities: coaxial, AES/EBU or TOSLINK. (i2S makes only occasional appearances).

    Over-simplistic thinking – and thinkers – tell us that all digital connections between streamer and DAC sound identical. That the bits comprising the digital audio signal are exactly that – bits – and that as long as they all arrive intact, a high-end audio streamer’s USB output, like that found on the Innuos Zenith MKII SE, will sound identical to that of a Raspberry Pi.

    Real-world experience, time and again, says otherwise. Not just this reviewer’s own experience with many streamer/DAC combinations but that of the many thousands of audiophiles worldwide who hear the audible improvements over an Apple Mac/book/Mini or Windows PC/laptop wrought by a bespoke network streamer; and who have made (sometimes spendy) spending decisions accordingly.

    What’s going on? Why isn’t digital audio transmission simply a matter of ones and zeroes? Why aren’t bits “just bits”?

    I asked this of Gordon Rankin at RMAF 2018. Now I’m inviting Innuos’ R&D Director Nuno Vitorino to weigh in with his thoughts.

    In keeping his answers digestible by non-engineering types (like yours truly), Vitorino asserts that one of the biggest challenges in designing good sounding USB outputs is minimising their electrical noise leakage — noise that can disturb the downstream DAC’s clock accuracy; that galvanic isolation might prevent noise from seeping along a USB connection’s power lines but not its data lines; that TOSLINK, which offers a 100% electrically isolated connection, is unfortunately many times higher in jitter than a well-designed USB (or coaxial) output…and will often sound worse; that transceivers converting a TOSLINK connection’s light back to an electrical signal can introduce their own noise; a finding that, in turn, has implications for an Ethernet connection’s optical isolation.

    Listen to our 30-minute conversation here:

    The overarching message from Vitorino is that there are no hard and fast answers in digital audio. Questions like “Isn’t Ethernet better than USB?” or “Is Ethernet better than WiFi?” are entirely system and implementation dependent.

    The take away is that the dogma – and the dogmatic – should be ignored and instead we should listen for ourselves. Same as it ever was.

    Further information: Innuos

    Written by John

    John currently lives in Berlin where he creates videos and podcasts for Darko.Audio. He has previously contributed to 6moons, TONEAudio, AudioStream and Stereophile.

    Darko.Audio is a member of EISA.

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    Volumio goes Primo!