Dolby TrueHD: What is this? complete explanation

What is Dolby TrueHD

Dolby TrueHD is One of the uncompressed (lossless) audio formats. It uses the Meridian Lossless Packing (MLP) lossless compression algorithm. A Dolby TrueHD digital stream can hold up to 14 separate audio channels. But in practice works with 6 (5.1) or 8 (7.1) channels. It supports up to 24 bits and 192 kHz sampling rates (for a maximum uncompressed stream of 63 Mbps!). But Blu-ray currently has a maximum of 8 channels at 24 bits and 96 kHz (or alternatively, 6 channels with 24 bits and 192 kHz) for a maximum compressed stream of 18 Mbps.

Surround Sound

It is one of several surround sound formats developed for home theater use.

In particular, Dolby TrueHD may be part of the audio portion of the Blu-ray Disc and HD-DVD software. It has retained its presence in the Blu-ray Disc format. But its direct DTS competitor, called DTS-HD Master Audio, is used more frequently.

TrueHD can support up to 8 channels of audio at 96kHz/24bit. While 24bit represents the sound with a bit of depth). Blu-ray discs that include DTH can use these options as either 5.1 or 7.1 channel audio at the studio’s discretion.

DTH also supports data rates up to 18Mbps (to put this into perspective – for audio, it’s fast!).

Lossless Factor

Dolby TrueHD (and also DTS-HD Master Audio) are referred to as lossless audio. This means that, unlike Dolby Digital, Dolby Digital EX, or Dolby Digital Plus. In other digital audio formats such as MP3, a type of compression is used that does not result in loss of audio quality between the original source as recorded and what you hear when played back content.

In other words, during the encoding process, information from the original record is not discarded. What you hear is what the content creator or engineer who has mastered the Blu-ray disc soundtrack wants you to hear.

Dolby TrueHD encoding even includes automatic dialogue normalization to help balance the center channel with the rest of your speaker settings.

Access to Dolby TrueHD

Dolby TrueHD signals can be transmitted from the Blu-ray Disc player in two ways.

1. One way is to send a compressed encoded bitstream over HDMI (version 1.3 or later) connected to a home theater receiver. That has a built-in Dolby TrueHD decoder. Once the signal is decoded, it is sent from the receiver’s amplifiers to the correct speakers.
2. The second way to send a Dolby TrueHD signal is to use a Blu-ray Disc player to decode the signal internally (if the player provides this option) and then send the decoded signal directly to a home theater receiver as a PCM signal via HDMI, or via a 5.1/7.1-set. channel analog audio connections, if this option is available on the player. When using the analog 5.1/7.1 option, the receiver does not need to do any additional decoding or processing. It simply sends the signal to the amplifiers and speakers.

Not all Blu-ray Disc players have the same internal Dolby TrueHD decoding options. Some may only provide internal two-channel decoding rather than full 5.1 or 7.1 channel decoding capability.

Unlike Dolby Digital and Digital EX surround sound formats. Dolby TrueHD (not decoded or decoded) cannot be transmitted over digital optical or digital coaxial audio connections. That is commonly used to access Dolby and DTS surround sound from DVDs and some streaming video content. The reason for this is that there is too much information, even in compressed form. For these connection options to accommodate Dolby TrueHD.

Implementation

It is implemented in such a way that if your home theater receiver does not support it. If you use a digital optical/coaxial connection instead of HDMI for audio, the default Dolby Digital 5.1 soundtrack is automatically played.

Also, on Blu-ray discs that have Dolby Atmos soundtracks. If you don’t have a Dolby Atmos compatible home theater receiver, you can access the Dolby TrueHD or Dolby Digital soundtrack. If this is not done automatically, it can also be selected via the playback menu of the corresponding Blu-ray disc. In fact, it’s interesting to note that the Dolby Atmos metadata is actually put into the Dolby TrueHD signal. So backward compatibility is easier to accommodate.

For all the technical details involved in building and implementing Dolby TrueHD. Check out two Dolby Labs’ white papers on lossless audio performance and audio encoding for future entertainment formats.