Ok, considering there is a wealth of info on audio codecs, I will post the whole info page here. This is an overwhelming amount of info, but you may find answers to many questions in this.A GUIDE TO HOME THEATER AUDIO CODECSDOLBY SURROUND SOUND
Originally Posted by nrighton
Thanks for the reply. If the 2550 can not internally decode the DTS MA audio, what is it sending to the analog outputs when I select DTS MA in the movie's audio setup menu ?
Dolby Surround Sound, the earliest form of surround sound, is a three-channel system. The Dolby stereo track is decoded into the front left and front right speakers, and a mono signal is sent to the two rear surround speakers. Since Dolby Surround signal can be encoded in a stereo analog signal, it is called a Matrix surround system. The process of extracting several channels from a 2-channel system is called Matrix surround decoding.DOLBY PRO LOGIC SURROUND SOUND
Dolby Pro Logic, introduced in 1987, added a center channel to Dolby Surround. The four channels were front left, front right, one center channel, and one mono matrix surround channel. The frequency of the surround channel was limited up to 7kHz. Dolby Pro-Logic was available on HiFi VHS and analog TV broadcasts in the United States.
Cables Needed: RCA analog stereo cables.DOLBY DIGITAL (AC-3) SURROUND SOUND (DD)
Dolby Digital (also known as Dolby AC-3, short for audio coding 3) was introduced in 1996. Dolby Digital content first appeared on LaserDisc. Hi-Fi VHS only supports up to Dolby Surround Pro-Logic. Dolby Digital is the standard for DVD-Video and is also part of the High Definition TV (HDTV) standard in the United States.
The Dolby Digital surround sound format provides up to five discrete full frequency (from 20Hz to 20,000Hz) channels (front left, front right, center, surround left, surround right), plus an optional sixth channel for Low Frequency Effects (LFE). The low frequency effects channel contains only low bass frequencies (3Hz to 120Hz).
Dolby Digital offers a maximum bit rate of 640kbps. Both Blu-Ray and HD-DVD players are required to support DD at its maximum bit rate.
Cables Needed: Toslink (Optical) or Coaxial S/PDIF (Sony/Philips Digital Interconnect Format), HDMI, and Multi-Channel Analog Cables (see footnote). For differences between the two cables, see A Guide to Optical, Coaxial, and Speaker Cable.
DIGITAL THEATER SYSTEMS (DTS) DIGITAL SURROUND
An alternative and competing format to Dolby Digital is DTS Digital Surround. The basic difference between these two formats is the method of compression. The use of DTS Digital Surround is optional on DVDs and it is not supported by HDTV or digital satellite broadcasting in the United States.
Some audiophiles claim that DTS is better in sound quality than Dolby Digital because it offers more data rates. The main disadvantage of DTS is that it uses more disc capacity. There are more DVD titles with Dolby Digital soundtrack than DTS.
Both Blu-Ray and HD-DVD players are required to support DTS at its higher 1.5Mbps bit rate.
Cables Needed: Same as Dolby Digital.
COMPARISON OF DOLBY DIGITAL AND DTS DIGITAL
Both DD and DTS use lossy data reduction techniques for soundtracks in order to minimize the limited space available on a DVD. Dolby Digital can be encoded in 192Kbps (reserved for 1.0 or 2.0 soundtracks and generally lower quality), 384Kbps (better quality), 448Kbps (used on the majority of DVD 5.1 soundtracks), and up to 640Kbps. DTS can be encoded in 754Kbps (the most commonly used), or a maximum rate of 1.5Mbps (very seldom seen). Theoretically, the less compression used in the encoding process, the better the sound quality will be. However, Dolby and DTS use different compression techniques, and their bit rates are not directly comparable to one another. While 448Kbps Dolby Digital encoding is better than 384Kbps Dolby Digital encoding, 754Kbps DTS Digital encoding is not necessarily better than 640Kbps Dolby Digital encoding.DOLBY DIGITAL EX (THX SURROUND EX) AND DTS EXTENDED SURROUND (DTS-ES)
In November 2001, Dolby Laboratories began to license the Dolby Digital EX (jointly developed by Lucasfilm's THX division and Dolby Laboratories.) Shortly afterwards, DTS introduced DTS-ES. Both Dolby Digital EX and DTS-ES introduced a new surround back channel. However, the information in the back channel (either one or two speakers) was encoded into the surround left and surround right channels (similar to the way the center channel is encoded for Dolby Pro-Logic). The extended surround formats are fully backward compatible.
Because the surround back channel is not a discrete channel, the correct way to refer to these two formats is Dolby Digital 5.1 EX Matrix and DTS 5.1 ES Matrix. It would be misleading to refer to them as 6.1-channel or 7.1-channel formats.
DTS-ES Discrete 6.1: A true 6.1-channel format
DTS-ES optionally supports a discrete full-bandwidth surround back channel, independent from the surround left and surround right channels. This is called DTS-ES Discrete 6.1.
Cables Needed: Same as Dolby Digital and DTS Digital.DOLBY PRO-LOGIC II & DOLBY PRO-LOGIC IIx
Dolby Pro-Logic is very disappointing when you play a CD or stereo album through it. For this reason, Dolby Laboratories introduced Dolby Pro-Logic II (DPL II). It creates 5.1 discrete channels (5 channels are full-bandwidth) from stereo CDs, old Dolby Surround movies, Laser Discs, and DVDs that were not mastered for 5.1.
Pro-Logic IIx, an enhancement over DPL II, converts any stereo or 5.1-channel audio input to 6.1-channel or 7.1-channel output. There are usually two or three modes: Music, Movies, and Games.
Cables Needed: Same as Dolby Digital and DTS Digital.
DTS Neo:6 is equivalent to Dolby Pro Logic II and IIx. It can convert stereo and matrix content (music or movie) to 5.1 or 6.1 full-bandwidth discrete channels.
Cables Needed: Same as Dolby Digital and DTS Digital.DTS 96/24
DTS 96/24 is a new and enhanced version of DTS Surround and allows encoding of 5.1 channels of 24-bit, 96kHz audio on the DVD-Video format. Prior to the introduction of DTS 96/24, it was only possible to deliver two channels of 24-bit, 96kHz audio on DVD-Video. It is fully backward-compatible with all DTS decoders. The DTS Encore, a new name used by DTS, simply adds more data to the old DTS formats to encode more information on the disc.
Cables Needed: Same as Dolby Digital and DTS Digital.DOLBY DIGITAL PLUS (DD+)
DD+ is a lossy format that uses a more efficient compression technique at data rates from 96Kbps to 6 Mbps, resulting in better sound quality. Although DD+ can support up to 7.1 discrete channels, the majority of Hollywood movies are only mixed for 5.1. Support for DD+ format is optional for Blu-Ray and mandatory for HD-DVD players. However, most movie studios prefer to use either basic Dolby Digital AC-3 or DTS Digital on their movie releases.
Cables Needed: Toslink (Optical) or Coaxial S/PDIF cannot carry a DD+ signal and will automatically play the standard Dolby Digital AC-3 track instead. HDMI cable is needed for transmission of DD+. If the player decodes DD+ to PCM, any version of HDMI connection can transmit the signal. If the player transmits the DD+ signal in bitstream, HDMI 1.3 connection is needed. Multi-Channel Analog Cables can also be used (see footnote).
DTS-HD HIGH RESOLUTION AUDIO (DTS-HD HR)
Similar to Dolby Digital Plus, DTS-HD High Resolution is an improved version of the previous DTS Digital formats. It is a lossy format that delivers up to 7.1 channels of sound with sampling frequencies from 48kHZ up to 96 kHz and 24 bit depth resolution. It runs between 1.5Mbps to 6Mbps. Note that DTS-HD HR is sometimes referred to as DTS-HD, which is misleading. Its quality is between DTS-HD Master Audio and the older DTS Digital 5.1 and DTS-ES.
This format is optional for Blu-Ray (up to a constant bit rate of 6Mbps) and HD DVD (up to a constant bit rate of 3Mbps) players. It is an alternative for DTS-HD Master Audio where disc space may not allow it. However, most studios prefer to use basic DTS Digital or Dolby Digital.
Cables Needed: Same as DD+, except if Toslink (Optical) or Coaxial S/PDIF cables are used, the player will send the standard DTS Digital Surround signal to the receiver.AUDIO CODECS FOR HIGH DEFINITION DISCSA BRIEF INTRODUCTION TO PCM, LOSSY, AND COMPRESSED LOSSLESS AUDIO
The audio on a Blu-Ray or HD-DVD disc is stored in either uncompressed linear Pulse Code Modulation (PCM), the compressed and lossless Dolby TrueHD, the compressed and lossless DTS Master Audio, the compressed and lossy Dolby Digital, the compressed and lossy DTS Digital algorithms, or combination of the above.
PCM is a procedure to represent an analog signal in digital form. Its accuracy is dependent upon the Sampling Rate and Sample Size.
Sampling Rate or Sampling Frequency is defined as the number of times samples are taken per second to convert an analog signal to digital. A higher sampling rate (e.g., 96kHz or approximately 96,000 samples per second) allows for higher frequencies to be represented.
Sample Size or Quantization is the number of bits used to represent the analog audio signal each time it is sampled in the analog-to-digital conversion process. A higher bit number allows a more accurate representation of the amplitude of the audio signal, resulting in better dynamic range.
The Bit Rate or Data Rate is the number of bits-per-second that can be processed. It is calculated by multiplying (sampling rate) x (sample size) x (number of channels).
Currently, the very best listening experience to end-users comes with Linear PCM coding on a disc. Unfortunately, 6 channels or more of high-resolution sound take up way too much bandwidth even on a high definition disc format. Using lossy perceptual compression codecs, such as MPEG, Dolby Digital, and DTS, is one solution. Perceptual lossy compression techniques throw away the least significant bits of the audio input. Theoretically, they represent detail that is impossible to hear, or at least difficult to hear. Unfortunately, a lossy codec compresses content such that the result, when decompressed, is not exactly the same as the original master.
Unlike perceptual lossy data reduction, a lossless codec compresses the data without losing any of it when it is decompressed. The result, when decompressed, is exactly the same as the original, with no compromises. Meridian Lossless Packing (MLP), developed by the British high-end audio manufacturer for DVD-A is the original compressed and lossless techniques for recording high resolution audio on a disc. MLP is licensed by Dolby Laboratories and enables up to six channels of 96 kHz/24 bit audio, or two channels of 192 kHz/24 bit audio onto a DVD-Audio disc. Dolby TrueHD, used in Blu-Ray and HD-DVD is based on MLP, and adds 8 or more full-range channels at higher bit rates. DTS Master Audio uses a different compression algorithm.
THE NEW AUDIO CODECS FOR BLU-RAY AND HD-DVD
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.LPCM
LPCM has existed since the days of CDs, but now it can carry 5.1 or 7.1 channels of audio, at higher sampling rates and bit depth as opposed to the 2 channel audio found on CDs. 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. LPCM is uncompressed audio, so it requires a lot of storage space.
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
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
48,000(samples per second) x 20(bits per sample) x 6(channels) = 5.8Mbps
48,000(samples per second) x 24(bits per sample) x 6(channels) = 6.9Mbps
48,000(samples per second) x 16(bits per sample) x 8(channels) = 6.1Mbps
48,000(samples per second) x 20(bits per sample) x 8(channels) = 7.7Mbps
48,000(samples per second) x 24(bits per sample) x 8(channels) = 9.2Mbps
96,000(samples per second) x 16(bits per sample) x 6(channels) = 9.2Mbps
96,000(samples per second) x 20(bits per sample) x 6(channels) = 11.5Mbps
96,000(samples per second) x 24(bits per sample) x 6(channels) = 13.8Mbps
96,000(samples per second) x 16(bits per sample) x 8(channels) = 12.3Mbps
96,000(samples per second) x 20(bits per sample) x 8(channels) = 15.4Mbps
96,000(samples per second) x 24(bits per sample) x 8(channels) = 18.4Mbps
192,000(samples per second) x 16(bits per sample) x 6(channels) = 18.4Mbps
192,000(samples per second) x 20(bits per sample) x 6(channels) = 23.0Mbps
192,000(samples per second) x 24(bits per sample) x 6(channels) = 27.7Mbps
BDA format specifications, p.18 limit the audio to 6 channels of 192kHz/24bit.
Please remember that since Dolby TrueHD and DTS HD MA 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.BITSTREAMING HD AUDIO
Dolby TrueHD and DTS-HD MA compress the LPCM audio signals without any loss of original data in order to save space on a disc. When the saved signals are decoded and decompressed, we will get LPCM signals again.
If the disc player decompresses and decodes the compressed audio, it will send the LPCM signals to the receiver. The receiver will then covert the LPCM signals from digital to analog for playback through the speakers. Alternatively, the compressed Dolby TrueHD or DTS HD MA signals can be sent by the payer in raw digital format to the receiver (PS3 cannot do this) for decoding to LPCM and digital-to-analog conversion. This process is called Raw Bitstream Transport, High Bit Rate Audio Streaming, or Direct Digital Audio Mode, depending on the manufacturer. Bitstreaming is the preferred choice of many critical listeners.
If the player decodes the high resolution audio to PCM, any version of HDMI can transmit the signal to the receiver. If the player sends the signal in native digital Bitstreams to the receiver, HDMI terminals on both the disc player and the receiver must be version 1.3, and the receiver must have the ability to decode high resolution audio codecs.
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.THE IMPLICATIONS OF DIGITAL BITSTREAMING ON AUDIO IN BONUS VIEW FEATURES
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 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.CONCLUSIONS
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 player (both Blu-Ray and standard DVD) 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.
7. 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.
8. Currently, the PS3 is not capable of carrying the high definition audio signals in bitstream format.
9. LPCM, the purest form of audio encoding on a disc, is lossless and uncompressed. However, it takes a lot more disc space.
10. Dolby TrueHD and DTS Master Audio are both lossless and compressed form of audio encoding. They take significantly less space on a disc.
11. There are no major audio quality differences between LPCM, Dolby TrueHD, and DTS Master Audio.
12. 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.FOOTNOTE
When a disc player is connected to a receiver with multi-channel analog cables, the player must perform digital to analog decoding and send the analog signal to the receiver. In this case, calibration and bass management adjustments such as speaker sizes and channel levels should be done in the player's setup menus or the receiver must have bass management for the 5.1, 6.1, or 7.1 ANALOG inputs. If the player lacks calibration adjustments or the receiver cannot perform adjustments for analog inputs, bass management cannot be performed.
ADDITIONAL INFORMATION AND REFERENCEShttp://www.dolby.com/consumer/techno..._overview.aspxhttp://www.dts.com/DTS_In_Consumer_P...e_Theater.aspxhttp://firstdtsstudio.hit.bg/dolby_vs_dts_eng.htmlhttp://www.hemagazine.com/node/Dolby...PCM?page=0%2C0http://en.wikipedia.org/wiki/Dolbyhttp://en.wikipedia.org/wiki/Digital_Theater_Systemhttp://en.wikipedia.org/wiki/SPDIFhttp://www.studioexperience.com/tech...s/dolbydef.asphttp://www.timefordvd.com/tutorial/SurroundSound.shtmlhttp://www.axiomaudio.com/dolbyprologicII.htmlhttp://www.audioholics.com/education...of-the-formatshttp://www.engadgethd.com/2007/04/26...d-demystified/http://news.digitaltrends.com/talkback145.htmlhttp://www.highdefdigest.com/news/sh...Explained/1064http://www.emedialive.com/articles/r...leid=11397#iiahttp://www.digital-digest.com/articl...ide_page6.htmlhttp://www.engadget.com/2007/06/17/b...ments/8145972/
High Definition Audio, Home Theater Magazine, May 2008, pp.36-40.