Blu Ray Audio….. What you need to know!

Background                                                                                                                           The standard DVDs you own now all use “lossy” multi-channel soundtracks, developed by Dolby Labs and Digital Theater Systems (DTS). “Lossy” means that a lot of data are thrown away using perceptual coding in order to greatly reduce the amount of “digital” space occupied on the disc by the soundtracks.

The perceptual coding is very sophisticated (it’s based on the principle that sounds softer than you can detect in the presence of louder sounds at or near the same frequency do not need to be encoded). This process enables Dolby Digital and DTS to carry six-channel discrete soundtracks (five channels plus a “.1” low-frequency effects channel), which run at relatively low data rates even when compared to the data rate from a lossless two-channel format like Compact Disc’s “Red Book” PCM (pulse-code modulation).

While lossy formats like Dolby Digital 5.1 and dts can–and do–sound really excellent, far better than the old analog soundtracks of the past, anyone would agree that lossless soundtracks such as those offered on Blu-ray are preferable if enough space is available on the disc. Just to emphasize, a PCM audio track like that from a compact disc is lossless: it’s a stream of “1s” and “0s” that precisely describe the frequencies and relative loudness (amplitude) of a music signal. No data are discarded to conserve bandwidth. And Blu-ray’s new lossless soundtracks use sampling rates and word lengths greater than compact disc and have the considerable potential to sound superior to the existing lossy Dolby Digital/dts formats.

The Blu-ray Soundtracks
The three lossless audio formats associated with Blu-ray players’ high-resolution audio soundtracks are Dolby TrueHD, DTS-HD Master Audio (MA) and Linear PCM (Linear Pulse-Code Modulation). These formats will all convey eight discrete channels (7.1) of no-loss audio that exactly duplicate the original studio masters, but there are various ways of extracting the signals depending on how new or current your AV receiver is and what kind of input connections are available.

Older AV receivers
Owners of AV receivers that have a set of multi-channel analog input jacks — usually six or eight RCA female inputs — need not despair. As long as you get a Blu-ray player which has internal decoding of the aforementioned formats and that’s equipped with a full set of analog output jacks, then you can still connect and benefit from the impressive high-resolution audio included on most Blu-ray discs. Your AV receiver doesn’t need HDMI inputs or outputs as you can still route the 1080p video directly over HDMI cables to your TV display or projector, bypassing your AV receiver for Blu-ray video. You will require a set of six or eight analog RCA cables to link the Blu-ray player’s analog RCA audio output jacks to your AV receiver’s multi-channel analog input set.

If you don’t care or don’t want to be bothered connecting the analog eight-cable set, then you could still use an optical digital or coaxial digital output from the Blu-ray player to the AV receiver’s optical or coaxial input. Your AV receiver will extract a standard lossy Dolby Digital 5.1 mix from the Blu-ray disc’s Dolby Digital Plus soundtrack. The latter is a lossy audio format, so you can expect the audio to sound as good as any standard DVD’s Dolby Digital mix or maybe better, because Dolby Digital Plus runs at a higher data rate that your AV receiver’s chip set may benefit from.

Getting Lossless Audio via HDMI and PCM
Dolby TrueHD is based on the original Meridian Lossless Packing profile that was developed for DVD-Audio, in which eight channels are compressed to take up less space but then exactly reconstructed by the player so there are no losses. If you get a Blu-ray player that will “unpack” or decode Dolby TrueHD and output it via HDMI in PCM form, then you all you need is an AV receiver that’s capable of receiving multi-channel PCM via HDMI. Any version of HDMI cable will carry multi-channel PCM — including HDMI 1.0 through HDMI 1.3. However, your AV receiver must be able to deal with eight channels of PCM audio via HDMI connection.

The other method of extracting and hearing Dolby TrueHD is by what’s known as bit streaming: a raw data stream of Dolby TrueHD that is sent from the Blu-ray player via HDMI 1.3 to an AV receiver that has built-in decoding of Dolby TrueHD. So far, there are only a few AV receivers with this capability, however more and more will be appearing with each passing month.

DTS-HD Master Audio
Similar to Dolby TrueHD, the same requirements exist for extracting the DTS-HD lossless Master Audio tracks, which like Dolby TrueHD, can carry up to eight discrete audio channels. You must have a Blu-ray player that will internally decode DTS-HD MA or output it via a bitstream and HDMI 1.3 to a new AV receiver that has a built-in decoder for DTS Master Audio.


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