Sound United has come up with a solution to the crippling HDMI 2.1 bug found in high-end 8K AV receivers launched by its brands Denon and Marantz last year. The company has apparently given up trying to fix the receivers themselves, and is instead offering a free adapter kit to anyone who has bought one. 

The HDMI 2.1 bug in Denon’s and Marantz’s receivers was first revealed in October 2020 by the German language website Heise, which found that the fault lies with the HDMI 2.1 microchip supplied by Panasonic Solutions that powers the devices.

The faulty chip is incompatible with HDMI 2.1, it was revealed. So it meant that anyone trying to pass a 4K signal at 120 frames per second through their Denon or Marantz receiver would only see a black screen. The same goes for 8K at 60fps signals. Strangely though, the HDMI 2.1 output in both receivers was reported to work just fine with the PlayStation 5 console as it remains within that machine's maximum bandwidth for HDMI 2.1, but not the new Xbox Series X console or graphics cards from Nvidia and AMD.

The problem for both Denon and Marantz is that because the issue has to do with the underlying hardware, it cannot be fixed through a firmware upgrade.

Sound United, which owns both the Denon and Marantz brands, has since confirmed the issue on its support pages. 

"4K/120Hz RGB signal (8-bit, 10-bit, 12-bit) is confirmed to be affected by this issue," the Denon support page reads. "Other 4K/60Hz and 4K/120Hz YCbCr 4:2:0 signals (8-bit) are confirmed to work without issue."

The 4K/60 and 4K/120 signals are both unaffected because they fall within the capabilities of conventional HDMI 2.0. 

As a temporary fix, Sound United advised users to bypass the receiver and instead connect their console directly to the TV, then use the TV’s HDMI eARC port to output sound to the receiver. But while that works, it kind of defeats the object of buying an HDMI 2.1 receiver in the first place, because most HDMI 2.0 receivers support eARC too. 

The new Denon and Marantz HDMI adapter kits appear to be the best solution that Sound United can come up with then. The additional box works by converting the signal it receives from the console to something the receiver can understand. 

"The SPK618 HDMI adapter solution is designed to remedy a compatibility issue between select Denon A/V receivers that support 4K/120Hz and 8K video resolutions and select gaming consoles that support 4K/120Hz and 8K video resolution output,” a statement from Denon reads. “If you experience a black screen and no audio when trying to pass through 4K/120Hz or 8K signals from gaming devices connected to the 8K input of the Denon A/V receiver, this adapter will help you to get a proper gaming experience.”

Marantz’s support page states something similar, and owners of both receivers are being encouraged to register for the free adapter from May 15. 

The HDMI 2.1 bug notably also affects Yamaha receivers too. Yamaha has also suggested using HDMI eARC as a temporary fix, but for the time being the company has said that it is "still investigating" the issue and how to respond.  

"We will address the reported HDMI 2.1 issue via future updates in order to provide customers with the best solution available but it requires time to clarify all the issues around HDMI2.1," the company told FlatPanels HD in a statement.