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HDMI Audio Transmission for Blu-ray and HD DVD

by April 04, 2007
Toshiba HD DVD Player

Toshiba HD DVD Player

We are seeing the following common questions from our readers regarding what happens when they connect their new Blu-ray Disc (BD) or HD DVD player to their A/V receivers or processors via HDMI. Some of the latest generation receivers are HDMI 1.2 compliant allowing them to handle multi-channel PCM audio from these new high definition formats. But what exactly are they transmitting?

Check out our little FAQ session with Craig Eggers of Dolby Labs to find out:

What signal does the receiver receive? (IE. PCM decoded DD+/TrueHD)

The receiver would receive a multi-channel PCM signal that has been decoded from the original source content by the Optical Player. Hence the player is doing the decoding and sending the data out as multi channel PCM to the receiver or processor.

In what resolution does the receiver receive the content ( Ie. 96 kHz / 24-bit or downconverted to 44 kHz / 16-bit)?

If the player has a lossless decoder, then it must output the source unaltered into the mixer. If the mixer does not have a downsampler (sample rate conversion), then the final PCM is the same sample rate as the source. If the mixer uses sample rate conversion, which could mean 48 kHz sources are upsampled to 96k, or it could mean 96k sources are downsampled to 48 kHz, then the output frequency does not match the source. I am not presently aware of any players with sample rate conversion. I am also not aware of any players that convert PCM from 24-bits down to 16-bit.

What advantages are there in having the receiver (HDMI 1.3) do the actual decoding as opposed to the HD DVD/Blu-ray Disc Player?

Potentially there is no difference for HD DVD. HD DVD discs authored as Advanced Content require the audio to be decoded and mixed. Presently that process occurs in-player. In BD, there is also little to no difference, since the decoders in the players are often the same as the decoders in the receivers or processors.

Please List Some advantages of next generation receivers or processors with HDM 1.3

  • If the player does not offer full 24/96 processing, then passing the bitstream to a connected AV receiver equipped with decoding and processing is an option.
  • Full, uncompromised processing of all PCM sources (and high definition digital video) as well as full backward compatibility is possible.
  • An AV receiver equipped with Dolby Digital Plus can decode all legacy Dolby Digital streams as well as Dolby Digital Plus and Dolby TrueHD streams from existing and future set-top boxes and devices that can play high-definition movies.

Editorial Comments about Future HDMI 1.3-enabled Receivers

As it stands right now, HD DVD and Blu-ray Disc players are doing all of the work typically done at the receiver/processor side to decode the multi-channel audio soundtracks. So far our listening experiences with the new HD DVD players passing the high resolution audio via HDMI as multi-channel PCM to the receiver have been very positive. But, one wonders just how much better the audio experience could be if the player itself wasn’t converting the audio to multi channel PCM via HDMI, or  re-encoding it to pass as a DTS bitstream via a toslink connection. Starting late this summer, we should start seeing HDMI 1.3 enabled receivers hit the store shelves from the likes of Denon, Sherwood Newcastle, Yamaha, and others. Until then, we keep eagerly awaiting the day for setting up comparative testing between having the player doing the decoding versus having the receiver/processor handling the entire audio processing.

Related Articles

Dolby TrueHD Overview

Dolby Digital Plus Overview


About the author:
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Gene manages this organization, establishes relations with manufacturers and keeps Audioholics a well oiled machine. His goal is to educate about home theater and develop more standards in the industry to eliminate consumer confusion clouded by industry snake oil.

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