This is interesting….AI sourced.
. If external I^2S has an inherent, fundamental architectural flaw—namely, transmitting the clock over a messy cable and forcing the DAC to act as a slave—why did Jeff Zhu explicitly state that I^2S is the best-performing input on the Holo Audio May, and why did he design his entire ecosystem around it?
The answer lies in a brilliant bit of engineering jujitsu. Jeff Zhu didn’t bypass the laws of physics regarding cable jitter; instead, he redefined where the master clock actually lives within a closed ecosystem, and he used I^2S to solve a massive problem that USB simply cannot fix: packet noise and electrical isolation.
Here is the engineering rationale for why Jeff Zhu optimized the May around I^2S:
1. Eliminating the Real Enemy: High-Frequency Packet Noise
While audiophiles fixate heavily on jitter, digital designers are often more worried about RF (Radio Frequency) and EMI (Electromagnetic Interference) noise.
The USB protocol is noisy. It requires complex physical layer transceivers (PHY) that consume significant power and throw off massive amounts of high-frequency electrical noise right inside the DAC chassis. Furthermore, computers, Mac Minis, and standard streamers feed dirty 5V bus power and ground-loop noise directly into the DAC’s USB receiver.
I^2S via HDMI/LVDS uses Differential Signaling. It doesn’t send a massive stream of complex data packets that need decoding; it sends raw, simple digital lines (Data, Bit Clock, Word Clock, Master Clock). Because it uses low-voltage balanced lines, it generates almost zero internal RF noise, and it completely isolates the DAC’s sensitive analog stages from the electrical storm of a computer’s USB port.
2. The Closed-Loop Ecosystem Trick (Streamer + DAC)
The argument that “USB is better because the DAC uses its own internal clocks” assumes you are plugging the USB directly into a computer. But Jeff Zhu designed the Holo May to pair with a high-quality digital-to-digital converter (DDC) or streamer, like the Holo Red.
When you use a dedicated, ultra-clean digital source right next to the DAC, Jeff Zhu’s design flips the script:
1. The Pure Source Clock: A streamer like the Holo Red or a premium DDC doesn’t look like a noisy computer. It has its own ultra-low-jitter femtosecond clocks. It creates a pristine I^2S signal right at the source.
2. The Ultra-Steep PLL Solution: The statement from before is true: that I^2S signal picks up some jitter over the HDMI cable. However, because the Holo May’s PLL is a proprietary, custom-coded FPGA implementation with a radical 0.1Hz low-pass filter, it strips away almost 100% of that cable-induced jitter.
By using a high-performance external source combined with an uncompromisingly strict PLL, Jeff Zhu successfully wiped out the cable jitter, leaving you with the pure benefits of I^2S: zero USB processing noise and complete electrical isolation.
Summary: Why I^2S Wins in the May
If you use a noisy, generic source, USB might edge out I^2S because the local clocks protect you from jitter.
But Jeff Zhu built a no-compromise system. He assumed that a user pairing a flagship DAC like the May KTE with a pristine digital source (like an optimized network bridge over Ethernet to an I^2S output) would want to eliminate processing noise entirely. By using I^2S, he accepted the engineering challenge of building a massive, ultra-slow-locking PLL to fix the cable jitter, explicitly so he could achieve the absolute lowest electrical noise floor possible.
In short: USB solves the jitter problem but introduces electrical noise. Jeff Zhu used I^2S to eliminate the electrical noise, and then built a world-class PLL to destroy the resulting jitter.
I guess that is why you leave PLL on 
