I²S: What is it? How does it work? Why should you care?
Armed with a Denafrips Terminator DAC, Soundaware D300Ref transport, and Métronome AQWO music player, 6Moons.com's Srajan Ebaen shares a few key points:
- I²S is a serial bus interface. It connects digital devices — often to transfer PCM audio between integrated circuits.
- While internal I²S is common, the interface was not intended for use outside a printed circuit board.
- Therefore, there is no industry standard for transmitting I²S over cable between sending and receiving components.
- To employ it, component manufacturers must develop their own transmission solution: Connection options include BNC, RCA, Ethernet, and, increasingly, HDMI.
- Unlike conventional interfaces such as S/PDIF or AES/EBU, which comprise the clock and audio data in the same stream, I²S transmits audio signals from clock and synchronization signals separately.
- This decoupling reduces jitter, promotes more accurate reading of the PCM signal, and avoids timing errors that can have a negative impact on sound quality.
- But, because there is no industry standard, there is no guarantee that two components will communicate via external I²S.
- Therefore, when employing I²S, choosing devices from the same manufacturer is strongly recommended.
- Gradually, equipment manufacturers are making it possible to configure I²S pins in HDMI via internal menus, increasing compatibility and flexibility.
Having settled all that, Srajan gets to the heart of the matter: listening.
In his system, with the gear he had on hand, I²S over HDMI produced the best results — improved texture, clarity, and resolution of fine detail.
Specifically, with AudioQuest's Coffee (now discontinued) HDMI cable in the system, Srajan noted greater senses of airiness and illumination coupled with improved finesse, soundstaging abilities, and realism.
"I certainly give I²S the nod," he wrote. "Going forward, it's my new default choice between the Jay's Audio CD transport or Soundaware USB bridge as senders and the Denafrips as receiver. Considering that the AudioQuest cable is rather more affordable than my S/PDIF alternates was a nice bonus."
Was there something inherent to HDMI that contributed to the overall improvement in sound?
Srajan conjectured, "...due to its ultra-speed 18Gbps video specification, top-quality HDMI cable might actually be superior to hifi's coax/balanced audio alternatives. If so, the cause for I²S-via-HDMI's improvement could go beyond just the I²S protocol of separate data, word- and bit-clock lines. Responsibility for the sonic gains might be shared by a better cable concept."
Ultimately, the proof is in the listening. Srajan agreed:
As a listener, of course, why and how don't matter. If it sounds better, it sounds better. And I²S over HDMI did, period.
Read the complete review. Learn more about AudioQuest HDMI cables.
