The cable length talk from yesterday made me curious, so I bought a 2 meter HDMI 2.1 cable today and spent a few hours comparing 0.5 meters vs 2 meters.
I found posts claiming that the HDMI standard itself uses 2 meters as a reference length, and that any deviation from 2 meters whether longer or shorter requires the sender & receiver to do error compensation. So at least for home theater, 2 meters might be optimal. I don't think this applies to I2S though.
In my comparison I initially thought the longer cable length was better, because the sound was smoother, easier on the ears, and airier. But the more I listened, the more it seemed like a defect and not a feature. All sounds were kept at a distance, no matter the recording. With the 0.5 meter cable, there was more variability in sound, which to me means it's more true to the source and that it's bringing out the unique flavor of each recording more clearly. After a while the longer cable sound felt hollow and almost out of phase. The more distant and pleasant character became a source of frustration, because everything sounded the same. The airiness felt fake. This was my impression when listening with speakers.
To really decide once and for all which is best, I put on the HD 800, as they make comparisons with equipment ridiculously easy. With the 2 meter cable the stage width was noticeably wider, but also with a grainy layer on top, like digital noise. This was heard across all music. Changing to the 0.5 meters cable made the music sound more pure and clean. The grain was gone, the stage shrunk a bit in width, and the treble became a bit hotter. It felt like a more authentic reproduction of the source material, and more importantly it was more entertaining to listen to. It's hard to make the HD 800 dynamic and exciting, and with the 0.5 cable the Pegasus managed to do so. The 2 meter cable degraded the sound enough to make them sound sterile and analytical.
It'd be useful if someone with the right knowledge or equipment could tell us which HDMI cable length is optimal for I2S. But in my subjective experience after comparing 0.5 meters vs 2 meters for 3-4 hours, shorter is better.
