PCM or Bitstream output?

mhuk05

Well-known Member
Hello,

just finalising setting up my system. BUT when I started to play Star Wars (4) it only played in stereo when on AUTO (surround mode).

I could force into into 5.1 but discovered my DVD was set to PCM output; changed this to Bitstream and now it works fine.

Why? What's the difference? :rolleyes:

Panasonic S75 and Marantz SR5400
 

Zacabeb

Active Member
In bitstream mode, it will simply output the selected signal 'as is'. In PCM mode, it will decode the signal, downmix it into 2 channels and output a raw, uncompressed digital signal. The purpose is to permit a digital connection to equipment that cannot handle certain formats.

Most commonly this has to be done for MPEG sound. Initially, MPEG1 Layer 2 and PCM were the two mandatory sound formats for DVD Video in Europe. For the US market, instead of MPEG1 Layer 2, Dolby Digital was mandatory alongside PCM. As a result of market pressure, the DVD Forum soon established Dolby Digital as one of the mandatory formats also for Europe. All DVD Video discs must contain a soundtrack stream in at least one of the mandatory formats.

MPEG1 Layer 2 is supposedly still one of the mandatory formats, but since most home theater equipment does not support it, DVD Video players must be able to decode it and output 2-channel sound, downmixing if necessary. Since Dolby Digital is also one of the mandatory sound formats, DVD Video players are likewise required to be able decode and output 2-channel sound from any Dolby Digital soundtrack. DTS does not have this requirement since it's optional and not mandatory, but they still make decoding and outputting 2-channel sound from DTS tracks an option to manufacturers.
 

Warpaint

Active Member
PCM (Pulse Code Modulation) is the format that CD's are recorded in. They are by default in stereo. The PCM signal is uncompressed. Note that MP3's will be transmitted in PCM also. Althought the MP3 file is compressed it is uncompressed on the fly before the digital signal is sent to the amplifier.

Dolby Digital and DTS are transmitted using Bitstream. Once the digital signal is received at the decoder (your AV amplifier) it is uncompressed into an approximation of the original 2, 3, 5 or 6 channel signal.
 

mhuk05

Well-known Member
Now it makes sense. I think I changed the output to PCM when I was having problems playing a VCD and I didn't change it back.

Is there much of a difference between using the optical output vs the digital output for sound (from the DVD to the AV amp)? Pros and cons? I use an optical cable at the moment, because it came with the DVD player...

Thanks for the info- much appreciated! :)
 

Warpaint

Active Member
mhuk05 said:
Is there much of a difference between using the optical output vs the digital output for sound (from the DVD to the AV amp)? Pros and cons? I use an optical cable at the moment, because it came with the DVD player...

In my experience it makes little or no diffence when using a DVD player and AV amplifier and listening to DD or DTS material.

If you listen to a stereo source such as CD (PCM) then I would prefer the Coax electrical cable.
Optical tends to sound slightly dull and lifeless by comparison.
 
E

edinburgh160

Guest
yes, I tend to prefer the coax as well when watching movies. plus it frees up the optical for xbox games / Sky+
 

Reiner

Active Member
Is there much of a difference between using the optical output vs the digital output for sound (from the DVD to the AV amp)? Pros and cons? I use an optical cable at the moment, because it came with the DVD player...
No difference me thinks except for the mechanical qualities. Generally I prefer coax because it's more sturdy and cheap optical cables might cause problems (loose connections etc.), but if your coax is the cause for a ground loop an optical lead would help to solve that. In either case a decent lead should be sufficient, i.e. it's IMHO not necessary to shell out hundreds of pounds for it.
 

The latest video from AVForums

Maverick UK Premiere IMAX Review + Top Gun, Tom Cruise, Tony Scott and 4K + Movie/TV News
Subscribe to our YouTube channel
Support AVForums with Patreon

Top Bottom