Audio Format - PCM Bitstream or Dolby Digital?

[rmorit01]

Hello:

I purchased my first receiver in over 10 years and I had a question about audio formats. I have a HDTV cable box (scientific atlanta 8300HD -- Time Warner Cable). I can select the box to either output stereo, Dolby Digital or HDMI.

Since I have an HDMI capable TV (Samsung HL-S5087 - 1080p HDTV) I'm running the HDMI from the cable box to the TV. I then run an optical digital out from the TV to the receiver.

The receiver identifies that it is receiving a PCM Bitstream.

I was curious what the "Dolby Digital" selection would do on the cable box? I connected the digital optical out of the cable box to an optical in on the receiver. I noticed that the receiver would seem to detect the "dolby" feed.

So what is the difference between the "Dolby Digital" out and the HDMI running through the TV to the receiver (as a PCM bitstream)? Is one format better than the other?

Just want to ensure I'm hooked up correctly.

Thanks --

 

[JVC]

So what is the difference between the "Dolby Digital" out and the HDMI running through the TV to the receiver (as a PCM bitstream)? Is one format better than the other?

They are both digital, so no real difference in audio. Both are just a bunch of 1's and 0's.......

If your receiver has HDMI input and output, I'd go to receiver first, and then to tv, with HDMI cable. Since HDMI carries both video and audio, you wouldn't need the optical cable then. Also be easier switching between the sources. But, if your receiver doesn't have HDMI, I'd use HDMI cable from cable box to tv, for video, and digital audio cable (digital coax or optical), from cable box to receiver. May not be any difference, than going from tv to receiver, but just seems like it back tracking, in a way (to me). Either way is fine actually. You've done good.

 

[rmorit01]

Thanks --

My AVR is one of those HDMI receivers that does video via HDMI but audio is done by the digital ouputs.

This helps clarify for me that a PCM stream is "as good" as a dolby stream -- and the table in my AVR manual shows that it can actually "process" more functions on the PCM stream.

Hopefully, I have this correct --

Bob

 

[JVC]

The "Bitstream" is digital. That's how you get 5.1 surround from the cable box and your dvd player. PCM is analog stereo signal. PCM Bitstream, I figured to be digital, since you were getting surround sound with that signal. Different brands of equipment uses different terms.

We usually tell people to set the audio output from their dvd players, to Bitstream........not PCM, because of the explanation above. I don't know that I've seen PCM and Bitstream, in the same term like that before...........

 

[Nick250]

Thanks --

My AVR is one of those HDMI receivers that does video via HDMI but audio is done by the digital ouputs.

This helps clarify for me that a PCM stream is "as good" as a dolby stream -- and the table in my AVR manual shows that it can actually "process" more functions on the PCM stream.
Hopefully, I have this correct --
Bob

Bitstream is what you want, it's one of those no brain-er deals. Using Bitstream all the digital data gets sent to the receiver and the receivers takes it from there. Make sure your receiver's input control is set to "auto" as well.

Nick

 

[j_garcia]

PCM is NOT analog, it is digital, but it is normally stereo only. The digital stream is still technically a "bitstream" but it is a PCM stream. If you are getting surround, it is being matrix decoded (PLII, DTS NEO:6, etc...) by your receiver - you CANNOT get discrete surround this way. "Bitstream" or "Dolby Digital" is what you want.

 

[JVC]

Thanks for the clarification of PCM. I was told it was the analog stereo signal.
My mistake........

 

[rmorit01]

... you CANNOT get discrete surround this way. "Bitstream" or "Dolby Digital" is what you want.

First of all, I want thank everyone for the responses. I've learned a couple of things already in terms of setting up the equipment.

First, is that for best sound quality from the HDTV DVR/Cablebox I need to set it up as "Dolby Digital out" it will then send dolby digital via HDMI, coax and optical digital.

j_garcia can you help me out with explaining what is "discrete surround" (see below)?

I'm thinking that two the audio can be "processed" in two ways by the AVR (note, it is an HK-AVR 245).

If the input coming into the AVR is PCM 44.1khz (that is what it shows on the AVR disaply PCM 44.1khz, then the receiver can "apply" a number of different of processing modes on that input -- (manual for the AVR shows this) -- so for example I could switch the receiver to a Dolby mode X and the incoming PCM gets processed as if were a Dolby mode X (mode X being one of set of different modes of Dolby available).

If the input coming into the AVR is a "dolby encoded" stream the AVR can recognize that and switch to a mode that "decodes" that stream. I'm thinking this is what you mean by "discrete surround"?

So my question is what provides the best sound?
- A PCM input that then gets processed by the receiver into, lets say a dolby mode (x - just since there are so many)? or
- An already dolby encoded input that is decoded by the receiver?

I don't have a good mental model for "what" the AVR actually does based on the input.

Again, thanks for explaining this since once I get this correct I can setup the cables for the best sound --

Thanks -- Bob

 

[JVC]

The Dolby Digital setting is definately better than PCM.
Discreet surround means there are six or seven seperate channels mixed into the programming. In a 5.1, 6.1 or 7.1 system, the .1 is the subwoofer.

In a 5.1 system, there's the (1)front left, (2)center, (3)front right, (4)right rear, (5)left rear, (6)subwoofer.
6.1 system is the same, except that you add a rear center speaker.
7.1 system is the same as 5.1, plus you add (6)left back speaker, and (7)right back speaker. The right rear and left rear speakers in the 5.1 system, become left surround and right surround (basically move up to be side speakers), in the 7.1 system. Each speaker is connected to it's own seperate channel. except the 7th speaker, in 7.1 system. It's matrixed in, since there's no 7.1 sources.

The PCM signal that gets processed, is actually a simulated surround, made from a stereo signal. It's better than nothing, but not as good as real Dolby Digital 5.1/6.1. Watching standard def tv channels,can use the Pro Logic setting, and sound pretty good sometimes.
Good luck!

 

[rmorit01]

Thank you --

I've been switching between the TV digital optical out and the cable box and the DVD player -- I'm seeing how the input changes from that.

Thank you again -- you've educated me enough so that I could mess around with this and also enabled me to get the "settings" right in the cable box.

Thanks