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Re: Onkyo 905, can it handle AC3 ?
From the link in my first post...
Quote:
In the early 90's Dolby Laboratories and Pioneer developed a way to place a full 5.1 channels of discrete digital audio on a laserdisc. Since the standard was in place and there were already 4 separate 'tracks' for audio they couldn't add a new one for this data since it would probably break backwards compatibility. Older analog-only players they figured were few and far between so they decided to replace the right analog audio track. A mono soundtrack for the movie could still be placed on the left analog track with the regular standard stereo and/or Dolby Prologic encoded data on the two digital tracks. In place of the right analog audio track they placed a compressed digital signal which contains ALL of the 5.1 channels of Dolby Digital (DD for short) AC-3 encoded data. If you play a DD encoded disc and switch to analog audio you'll probably hear a 'hissing' sound in the right channel. This is the digital data for the DD 5.1 audio.
What many people are thinking is "Why can't I just hook a cable from my right audio output jack to the DD input of my receiver/decoder and get the data to it in that way?". You could IF it was not filtered and processed by the player's audio circuitry. Thd LD player does not know you're sending that data to an outboard processor for decoding. That output is supposed to be delivering formatted audio for a human's ears, not for input to a processor for further decoding.
Other people are thinking "Why can't I just hook a cable from the existing Coaxial Digital or TOSLINK Optical output on my LD player to the appropriate input on my receiver/decoder and get DD 5.1 sound that way?". Remember from the description above WHERE the Dolby Digital AC-3 data is stored on the laserdisc physically. It's on the RIGHT ANALOG audio track. The Coaxial or Optical digital outputs on an LD player output the PCM digital data stored on the two digital audio tracks of the disc or of course the digital audio data stored on a regular audio CD. There is no Dolby Digital AC-3 data stored on the disc on those two digital audio tracks and therefore any existing digital outputs on the player will NOT have any usable data as far as the receiver/decoder will be concerned.
How do you store "digital" audio data on an "analog" audio track? Dolby Digital as the name implies is a purely digital audio specification. Powerful computer chips take a stream of compressed digital audio and decode it and split it into anywhere from 1 to 5.1 channels of audio. This is performed inside the receiver or Dolby Digital decoder if the receiver doesn't have the decoder built-in. DD data is stored on the laserdisc in an RF (Radio Frequency) form. Technically it's QPSK modulated and resides within the 2.8Megahertz space allocated for the right analog audio track.
An LD player that came stock with an "AC-3 RF OUT" connector OR a player that has been modified for it output the same type of signal. It's a buffered RF signal which technically is analog. That analog data however represents the digital data in much the same way a modem can move digital data across an analog telephone line.
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- Walter. |