THE NEW AUDIO CODECS FOR BLU-RAY
The new audio CODECs on high definition movies are lossless, and are identical to the audio on the original master. The three lossless CODECs supported by Blu-Ray Disc and HD-DVD are LPCM, Dolby TrueHD and DTS HD MA. The difference between the three is the number of bits they use on the disc. LPCM is not compressed and takes a lot more space. Both Dolby TrueHD and DTS HD are compressed like a Zip file and use far less space, allowing more space on the disc for other features. LPCM also supports a higher sample rate than TrueHD or DTS HD, but remember that the sample rate is higher than most studio masters. It is estimated that a 2 hour movie with a 16-bit/24-bit, 5.1 soundtrack requires 4.14GB with LPCM versus 1.26GB for either TrueHD or DTS HD.
A PCM audio track is an exact copy of the original master, encoded on disc without compression. The main benefit is that it is simpler and maintains the quality of the master without any degradation that may occur from using a compression technique. The chief disadvantage is that it takes a lot of disc space. LPCM support is mandatory for Blu-Ray and HD-DVD players. Although the Blu-Ray Disc format is capable of using LPCM up to 24-bit resolution, studios may decide to use 16-bit resolution to save bandwidth, or if the bit resolution of the master does not require 24-bit encoding.
Cables Needed: Toslink (Optical) or Coaxial S/PDIF cannot carry a 5.1 LPCM signal, so the signal will be reduced to 2 channels only. However, any version of HDMI connection can carry the LPCM signal in full quality. Multi-Channel Analog Cables can also be used (see footnote).
Dolby TrueHD is a lossless compression codec. Although it is compressed to use less disc space than a PCM track, once decoded it is identical to the original master. Dolby TrueHD supports up to eight full-range channels (with room for expansion) of 24-bit/96 kHz audio (at the discretion of the studio) up to a maximum of 18Mbps bit rate. Support for Dolby TrueHD is optional for Blu-Ray players and mandatory for HD-DVD players.
Cables Needed: Toslink (Optical) or Coaxial S/PDIF cannot carry a TrueHD signal and will automatically play the standard Dolby Digital AC-3 track instead. If the player converts the TrueHD to PCM, the signal can be transmitted over any version of HDMI. If the TrueHD signal is transmitted via bitstream, HDMI 1.3 will be needed. Multi-Channel Analog Cables can also be used (see footnote).
DTS-HD MASTER AUDIO
DTS-HD Master Audio, previously known as DTS++, is another lossless audio codec similar to Dolby TrueHD. Although a DTS-HD MA track takes up more disc space than a TrueHD track, it does not require a secondary standard DTS Digital track for backward compatibility. DTS-HD Master Audio encodes virtually an unlimited number of channels at resolution of up to 24 bits and 192kHz and can downmix to 5.1 or 2 channels.
The use of DTS-HD Master Audio is optional for Blu-Ray and HD-DVD players. On Blu-Ray Disc, DTS MA supports up to 7.1 discrete channels at 96kHz/24bit or up to 5.1 discrete channels at 192kHz/24bit and up to a variable bit rate of 24.5Mbps. On HD-DVD, the maximum bit rate is limited to 18Mbps.
Cables Needed: Same as Dolby TrueHD, except if Toslink (Optical) or Digital S/PDIF is used, the standard DTS Digital track will be played.
ARE THERE ANY DIFFERENCES IN SOUND QUALITY BETWEEN THE THREE HD AUDIO CODECs?
LPCM soundtracks on Blu-Ray Disc and HD-DVD are not compressed. Dolby TrueHD and DTS-HD Master Audio are lossless codecs. They are compressed versions of the PCM track.
The maximum uncompressed bit rates for a movie soundtrack are approximately:
48,000(samples per second) x 16(bits per sample) x 6(channels) = 4.6Mbps
Dolby TrueHD and DTS HD MA can go up to
96,000(samples per second) x 24(bits per sample) x 8(channels) = 18.4Mbps
Please remember that since both CODECs use variable bit rates, we cannot calculate the average bit rate of a typical soundtrack. In addition, Dolby TrueHD and DTS MA use different compression algorithms and on the average use less than the maximum numbers.
Theoretically, LPCM, Dolby TrueHD, and DTS Master Audio should sound the same if they are encoded at the same number of bits and sampling frequency (16 bits, 48 KHz for example). Any difference that you may hear are due to channel volume differences.
Decoded Dolby TrueHD = Decoded DTS HD MA = Uncompressed LPCM
In the future, we will see less LPCM titles (especially at 24-bit, 96KHz, and 7.1-channels) since this will require a lot of disc space. TrueHD and DTS Master Audio are encoded at variable bit rate and compressed, leaving more disc space for better picture quality and more extras.
THE IMPLICATIONS OF DIGITAL BITSTREAMING ON AUDIO IN BONUS VIEW FEATURES
HDMI cable is the preferred way to transmit high resolution audio from a player to a receiver or pre-amplifier. If the player decodes the high resolution audio to PCM, any version of HDMI can transmit the signal. However, many critical listeners prefer to send the signal in native digital Bitstreams (PS3 cannot do this) to the receiver for conversion of digital to analog signals. In order to accomplish this, you must have HDMI 1.3 terminals on both the disc player and the receiver, and the receiver must have the ability to decode high resolution formats. Please note that transmission of audio signals in digital Bitstreams may be called High Bit Rate Audio Streaming or Direct Digital Audio Mode, depending on the manufacturer.
If the receiver does not have HDMI inputs, your only option is to use multi-channel analog cables (PS3 does not have multi-channel analog outputs), and you must rely on the player (assuming the player has all the decoders for the high-resolution audio formats) to perform all the digital-to-analog conversion. The main drawbacks to using analog connections is that your sound quality will be limited by the quality of the decoders, audio processors, and digital-to-analog convertors inside the player. Another problem with analog connections is that bass management must be handled by the player or the receiver must have the ability to handle bass management in analog domain.
As was mentioned earlier, many critical listeners prefer that all the processing and digital-to analog conversion be done in the receiver or pre-amp, which may have superior audio components. To do this, we need to send the audio signal in native digital Bitstreams to the receiver or pre-amp. The downside to sending the advanced audio codecs in native bitstream is that you can only send the movie soundtrack itself. Any secondary content, like menu beeps or the audio that accompanies Picture-in-Picture interactive features is not part of the original bitstream and will not be transmitted. Audio commentaries and alternative-language audio may also be affected, depending on how the disc was authored. The only way to send the additional content is by allowing the disc player to perform the audio decoding itself, during which the player mixes the new material on top of the movie soundtrack for transmission in either PCM or analog format. In some cases, you may lose the lossless soundtrack. If you are watching a movie with the Bonus View features enabled, and you want to restore the high resolution audio, it may require you to stop the disc playback to go to the player’s setup menu, and that can be a big nuisance.
THX, a company started by George Lucas, is not a sound CODEC like DD or DTS. It is a set of technical specifications in order to standardize the performance of surround sound systems. Manufacturers of A/V products are given a set of specifications that their products must meet in order to obtain the THX certification. Some manufacturers choose not to participate in the program, preferring to use their own specifications.
IMPORTANCE OF CALIBRATION
In order to enjoy the HOME THEATER AUDIO in the most optimum way, you need to calibrate your audio system and adjust your speakers/subwoofer. Although many new receivers have their own built-in calibration programs, I highly recommend the use of an SPL meter in addition to them. Radio Shack offers two excellent choices below $50. I also encourage you to read my thread on “Calibrating Your Audio with an SPL Meter”:
Pay close attention to the section at the end on subwoofer positioning and its interaction with the main speakers.
1. Optical (Toslink) and Digital S/PDIF cables cannot carry Dolby Digital Plus, DTS HD High Resolution Audio, LPCM, Dolby TrueHD, and DTS HD Master audio signals. You need an HDMI cable.
2. If the player converts the high definition signals to LPCM, any version of HDMI connection will successfully carry the signal.
3. If the player decodes the high definition audio signals to Bitstream, the HDMI connections of the player and the receiver must be version 1.3.
4. If multichannel analog cables are used to connect the player to the receiver, Bass Management must be performed by the player or the receiver must have the ability to perform bass management for analog signals. Please refer to the footnote.
5. If you are using PS3 as your disc (both Blu-Ray and standard DVD) player and your receiver does not have an HDMI connection, use an Optical cable and set the PS3's audio output to Bitstream. However, you will only get Dolby Digital or DTS Digital surround signals.
6. If you are using PS3 as your Blu-Ray player and your receiver has an HDMI connection, use an HDMI cable and set the PS3's audio output to LPCM. If you are using a standard DVD in PS3 and an HDMI connection, you can set the player’s audio output either to bitstream or LPCM.
7. PS3 is capable of carrying the high definition audio signals in bitstream format.
8. LPCM, the purest form of audio encoding on a disc, is lossless and uncompressed. However, it takes a lot more disc space.
9. Dolby TrueHD and DTS Master Audio are both lossless and compressed form of audio encoding. They take significantly less space on a disc.
10. There are no major audio quality differences between LPCM, Dolby TrueHD, and DTS Master Audio.
11. It is important to remember that only Blu-Ray and HD-DVD players and recorders are required to support the playback of the mandatory formats. Movie studios are free to decide which audio CODEC(s) they want to use for their movie releases.