Understanding 8-channel LPCM over HDMI: Why it Matters and Who Supports it

The Fix: 8-Channel LPCM over HDMI

But, Wait! There is a solution. It's ok to send uncompressed audio over HDMI, so in theory you could decode TrueHD/DTS-HD audio tracks in software and send them out as decoded, uncompressed LPCM without a Protected Audio Path.

Cyberlink, everyone's favorite player software manufacturer, supports decoding both TrueHD and DTS-HD MA in software (although it appears that Cyberlink does downsample the 24-bit 48kHz LPCM output to 16-bit 48kHz, but at least you get 8 discrete channels even if you lose the bit-for-bit lossless accuracy of the original signal).

With software support and no protection requirements to worry about, all we need is basic hardware support - and here's where most companies have failed miserably over the past couple of years.

It takes a lot of bandwidth to send 8-channels of uncompressed, 24-bit, 48kHz audio to the HDMI display engine. In the early days, GPU makers simply passed along SPDIF, which only offered 1.5Mbps - enough for 5.1 Dolby Digital, 5.1 DTS, or 2-channel LPCM to be sent over HDMI.

Intel guessed right enough to include a wide enough bus on its chipsets between the audio codec and the HDMI output engine to support up to 8-channel LPCM. NVIDIA eventually followed suit with its GeForce 8200 series of IGPs, while AMD is still lacking support for anything above 2-channel LPCM (although all three platforms can give you 5.1-channel DD/DTS over HDMI).

AMD has redeemed itself by being the first standalone GPU maker to offer 8-channel LPCM output over HDMI on discrete graphics cards with the RV7xx series of GPUs.

The Realtek codec in the Radeon HD 4800 series GPUs supports 8-channel LPCM over HDMI

Selecting 8-channel DTS HD MA in Rambo on Blu-ray

8-channel LPCM from the Radeon HD 4850 to an Integra DTC-9.8

It works!

Despite supporting 8-channel LPCM, the G45 still lacks a truly protected audio path and thus will never be able to send an encoded Dolby Digital TrueHD or DTS-HD MA signal over HDMI. I suspect that its successor in 2009 will finally add this functionality.

Whew. There you go, that's what all of this 8-channel LPCM talk is all about. It’s supported on NVIDIA’s GeForce 8200/8300 chipsets, Intel’s G965/G35/G45, and AMD’s Radeon HD 4800 and 4600 series. Done.