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SPDIF vs PCM vs Dolby Digital 5.1 (1 Viewer)

Tony DL

Auditioning
Joined
Nov 27, 2002
Messages
8
Recently my cable company has offered digital cable to my area. After about 6 months I finally received a box with S-Video and Digital audio outputs. The cable box has two options. 1) optical output and 2) SPDIF coax output. My digital receiver has two options, 1) optical input (which I have my DVD player hooked up) and 2) PCM inputs. Can I hook the SPDIF output from my cable box to the PCM input on my receiver. If so what is the difference between SPDIF/PCM/Dolby Digital 5.1. I have read in the forum about the technical formats etc. but have not been able to find a comparison between the three. Example, Will SPDIF and PCM produce a 5.1 channel surround sound if it has a digital feed from the source? Which has the best sound, etc.? Is there any other option since my receiver is limited to the one opticial input (which is hooked up to my DVD)and two PCM inputs? Can anyone help with this problem?


Thanks,
Tony
 

Bob McElfresh

Senior HTF Member
Joined
May 22, 1999
Messages
5,182
Hi Tony. Welcome to HTF!

A little background: there are 2 types of encodings, and 2 types of connections. PCM is what a CD player puts out, Dolby Digital is what a DVD player with a DVD movie puts out.

There are 2 types of digital connections: optical (called "Toslink") and coaxial-digital. Both types of connections can carry PCM and DD signals.

SPDIF (Sony Phillips Digital Interface) is the specificiations around which the digital connections are built.

Short Answer: use a Video cable to connect the coaxial output on your cable box to the coaxial input on your receiver. It should work, but my guess is the cable box will only put out PCM.

But here is a problem: on many CATV box's, you only get digital sound from the upper channels (like the ones numbered above 100). This means you should also connect up L/R audio cables.

Hope this helps.
 

Tony DL

Auditioning
Joined
Nov 27, 2002
Messages
8
Bob,

Thanks for the help. I still have questions about what type of sound quality I will be receiving from the PCM connection. Will this be a 5.1 channel output? Will it be the eqivilant to the 5.1 Dolby Digital as far as sound quality?


Thanks,
Tony
 

Hugo

Stunt Coordinator
Joined
Nov 21, 2002
Messages
147
Hi Tony,
PCM is not digital 5.1 channel output, it only outputs 2 channel stereo sound. Therefore you won't get the same sound quality as 5.1

Hugo
 

Bob McElfresh

Senior HTF Member
Joined
May 22, 1999
Messages
5,182
you wont get the same sound quality as 5.1
Well... lets be careful here.

A CD using PCM has a LOT more data per second than a DVD movie. In truth, it is a SUPERIOR feed.

The Dolby Digital data is highly compressed. The throw away 5 out of 6 parts of the sound. But they do it in a clever way and put things back so you dont notice.

Are you trying to get all your speakers to work using the CATV box as a source? Yes, you can do this.

Your receiver will take the STEREO signal using Analog cables or the PCM digital feed and can do ProLogic decoding. This will send dialog to the center speaker, music and effects to the front and rear speakers. This only works for shows that display the "Dolby Surround" logo near the begining.

Also, your receiver has things called "DSP" modes. Things like "Hall, Church, Jazz, etc." These will all take the STEREO signal and send sound to all your speakers to create an artifical environment.

Does this help?
 

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