Yamaha's first-gen HDMI 2.1 receivers are capped to 24Gbps bandwidth even after the HDMI board has been replaced. It is a potentially game-breaking limitation with Nvidia/AMD GPUs and Xbox Series X.
HDMI 2.1 woes
In May 2021, Yamaha announced an HDMI board replacement program to fix its defective first-generation HDMI 2.1 receivers (RX-A2A, RX-V4A and RX-V6A).
- "A free update program will be available starting in fall 2021 to update the HDMI board on these AV receivers to allow for the 4K/120Hz signal transmission," the company said in May.
It turns out (see this thread on AVSForum) that the replacement board is capped to 24Gbps bandwidth, which is too low to carry uncompressed 4K120 10-bit RGB from Xbox Series X and Nvidia/AMD HDMI 2.1 graphics cards. It is also too low to carry uncompressed 8K. You will get a black screen, unless you downgrade the signal before it reaches the receiver.
The HDMI 2.1 standard allows for up to 48Gbps bandwidth and while manufacturers are allowed to opt for 24Gbps or 40Gbps in a TV or console, an intermediate device like a receiver should not be the limiting factor – the weakest link – in the HDMI chain, i.e. 24Gbps.
Also read: HDMI ARC (Audio Return Channel) and eARC explained
No plans to offer 40Gbps upgrade
It is a significant limitation so why did Yamaha settle on 24Gbps and why is the limitation not being clearly communicated to customers on Yamaha's websites?
- "Because we purposed to avoid inconvenience of HDMI path through on gaming use. Key features for gaming, such as 120Hz flaming rate and VRR / ALLM / QFT, can work on 24 Gbps bandwidth. So, we chose this spec for these models. (Of course, these models have limitation on 8K60 uncompressed and 4K120 4:2:0 chroma sampling)," Yamaha wrote in a statement to FlatpanelsHD.
- "We are showing "8K60B, 4K120AB" on our website. "8K60B" means that the models have 24 Gbps limitation, and it was regulated by HDMI Org. So, We've recognized as no problem. However, we've found that it might lack politeness. Now, we're under considering to show an additional information on our website."
8K60B refers to an 8K60 signal compressed with DSC ('B' for compressed), which is not currently supported by most TVs and video players/consoles. 'A' refers to uncompressed.
The company stated that it has no current plans to offer customers of its first-generation HDMI 2.1 receivers, RX-A2A, RX-V4A and RX-V6A, an option to upgrade to a 40 Gbps HDMI 2.1 board.
Yamaha's second-generation HDMI 2.1 receivers, RX-A4A, RX-A6A and RX-A8A, and are equipped with an HDMI 2.1 board that supports up to 40Gbps bandwidth.