Eight channel PCM

A reader, Michael, has emailed me about a previous post. He says:

Another interesting post there. The Dolby email was quite interesting.I have older AVR without HDMI, so I have an interest in the ability of my receiver (RX-V757) to keep up with the new HD standards.

I was just wondering, when you talk about

let the player do the decoding, and send the six or eight channels in PCM format to the receiver

Are these analogue outputs on the player which then plug into the multi-channel inputs on the back of receivers?

Actually, I was talking about sending multichannel PCM down the HDMI cable. But you can also do it that way. Most players have 5.1 or 7.1 channel analogue outputs, so you can plug them into the multichannel analogue inputs of your home theatre receiver. The Toshiba HD-E1 HD DVD player seems to be the only exception at the moment. It offers only two channel analogue output.

So how can you receive multichannel audio from one of these players? There are four different ways.

First, if it has multichannel analogue outputs, you can use these. However, this is subject to the appropriate decoders being built into the player. If a player has no decoder for, say, DTS-HD then it will extract from this a regular DTS bitstream and decode that instead.

Second, you can use the regular optical or coaxial digital audio connection. In this case, the signal that will be fed to your receiver will be the Dolby Digital or DTS core, as appropriate, of the Dolby TrueHD, Dolby Digital Plus, DTS-HD Master Audio or DTS-HD High Resolution format, if any, on the disc. Although not necessarily. Toshiba players routinely convert Dolby Digital Plus to standard, high bitrate (1,536kbps) DTS for the digital connection. The reason for that is that Dolby Digital Plus is a mandatory standard for all HD DVD players, whereas it is optional for Blu-ray players. For this reason Blu-ray organises its DD+ bitstream into two parts. There is a regular Dolby Digital core (usually at 640kbps rather than DVD’s maximum of 448kbps), plus additional information which allows the full benefits of DD+ to be realised, if the player has a suitable decoder. Dolby TrueHD bitstreams on Blu-ray must have a regular Dolby Digital bitstream associated with them.

But since all HD DVD players can decode DD+ bitstreams (these are very common on HD DVDs), they consist of one cohesive bistream which cannot be divided up. So in order to send it down a standard digital connection, the sound must be decoded by the player and then re-encoded in a compatible format. The choices are two channel PCM, multichannel Dolby Digital or multichannel DTS. Toshiba appears to have decided, wisely, that people won’t want stereo when they could have multichannel, and that DTS probably offers slightly higher quality than Dolby Digital.

Third, if you have HDMI inputs on your receiver which the receiver actually uses (ie. it doesn’t simply act as a switchbox, but can read the audio) the player can decode the signal to multichannel PCM. I have checked a number of Blu-ray players and they do indeed do this, all the way up to 7.1 channels (except the Sharp BD-HP20X, which drops back to two channels if the signal has a 96kHz sampling rate and is encoded in 7.1 channel Dolby TrueHD — however it does decode to 7.1 channel PCM in normal 48kHz tracks). Toshiba HD DVD players max out at 5.1 channels for decoding to PCM.

Fourth, and finally, the Toshiba HD-XE1 with the latest firmware, the Pioneer BDP-LX70A and the Sony BDP-S500 Blu-ray players, can send some of the new high definition bitstreams down the HDMI cable to a HDMI 1.3 receiver which can then decode them itself. I have confirmed that this works for the Toshiba HD-XE1 with DD+, Dolby TrueHD, DTS-HD Master Audio and DTS-HD High Resolution. I have confirmed that this works for the Sony as well for DD+ and Dolby TrueHD, but not for DTS-HD Master Audio. Sony says it works for DTS-HD High Resolution, but I don’t have any Blu-ray discs with audio in this format to check.

I have also confirmed that the Pioneer does both kinds of Dolby as bitstreams, and I think it also does DTS-HD Master Audio. I seem to remember checking this, but I didn’t write it down and it was a rush job (the player was to be picked up the very day I had all the other pieces of equipment and test discs in place).

I hope that clarifies things!

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