Can anybody tell me

What the audio bitrate on my cable( Comcast) is for

1.watching a movie that is 5.1 on a hd channel

2. Watching that same movie on the lower non hd version of that channel that is 2.0 and my reciever is applying Pro logic to make it 5.1



Thanks!

Can anybody tell me

What the audio bitrate on my cable( Comcast) is for

1.watching a movie that is 5.1 on a hd channel
It depends. Most stations send 448 kbps for 5.1 audio but my NBC affiliate sends 384 kbps for 5.1.

2. Watching that same movie on the lower non hd version of that channel that is 2.0 and my reciever is applying Pro logic to make it 5.1
It depends. Some stations drop their audio bit rate for local programming, One station here drops it to 256 kbps. My CBS affiliate sends their "Descriptive Audio" DD2.0 channel at 192 kbps.

Your question doesn't match the title, but here goes:

5.1 DD on HD channel -- 384 kbps or 448 kbps
2.0 DD on SD channel -- anywhere from 192 to 384 kbps, depending on the encoder setting.

Thanks! Then a quick question. How come some channels sound so great (dvd comparable)....cbs, hbo, starz, and others...USA hd, SCI fi hd etc sound so much worse,( not even close to a good dvd)??

It doesn't have anything to do with the bit rate. It has everything to do with the quality of the audio they get and whether they add any additional processing. I suspect your "good" channels try to just pass what they get, and the "bad" ones process the audio to sound like a '70s TV or radio station.

USA, Sci-Fi - what do these have in common? Oh yeah they sound bad like their network sibling. :D

It depends. Most stations send 448 kbps for 5.1 audio but my NBC affiliate sends 384 kbps for 5.1.


It depends. Some stations drop their audio bit rate for local programming, One station here drops it to 256 kbps. My CBS affiliate sends their "Descriptive Audio" DD2.0 channel at 192 kbps.

Hmmmm......

Fox and TNT-HD are the only major channels to use 448 kbps. That does not mean most in book.

Your question doesn't match the title, but here goes:

5.1 DD on HD channel -- 384 kbps or 448 kbps
2.0 DD on SD channel -- anywhere from 192 to 384 kbps, depending on the encoder setting.

The BBC use DD 5.1 at 384kps for their HD broadcasts in the UK. They use either 192 or 256kbps 2.0 Stereo using MPEG Layer 2 audio for SD audio, and the Audio Description/Narration services for HD.

Not sure what Sky are using for their DD5.1 bitrate - they carry DD 5.1 streams on both their SD and HD movie channels.

Hmmmm......

Fox and TNT-HD are the only major channels to use 448 kbps. That does not mean most in book.

For 5.1, it is for my city's affiliates:

Fox: 448 kbps for 5.1
CBS: 448 kbps for 5.1
ABC: 448 kpbs for 5.1
NBC: 384 kbps for 5.1

The rest including my CW affiliate are DD 2.0.

Your affiliates may wish to save a few kbps for some reason.

I must say that it is unusual for a broadcaster to pay attention to things like audio bit rate. It is surprising to see a CBS and ABC station taking the time to set their encoders to 448 kbps. I wonder if they took care with the rest of the settings.

I'm surprised my local stations are the exception and that most stations around the country aren't sending 448 kbps. Is there any advantage to send 64 kbps less? It seems like pocket change in an ATSC stream and my NBC station certainly has less convincing surround sound.

I don't think many people would notice the difference between 384 kbps and 448 kbps. 384 kbps was originally suggested for DTV, while 448 kbps was chosen for DVD. The compression systems for DTV and DVD are identical.

384 kbps results in an upper frequency limit of around 15 kHz, comparable to the range for analog TV. 448 kbps results in an upper limit of about 20 kHz, comparable to CD. Eventually the data rate for DTV was allowed to include 448, but no one has ever required it to be changed.

I don't think many people would notice the difference between 384 kbps and 448 kbps. 384 kbps was originally suggested for DTV, while 448 kbps was chosen for DVD. The compression systems for DTV and DVD are identical.

384 kbps results in an upper frequency limit of around 15 kHz, comparable to the range for analog TV. 448 kbps results in an upper limit of about 20 kHz, comparable to CD. Eventually the data rate for DTV was allowed to include 448, but no one has ever required it to be changed.

Yep - that makes sense. In Europe (and elsewhere) some countries have been using 728kbps NICAM digital audio (for stereo and bi-lingual mono) since the late 80s. That used 32kHz 14->10 bit companding (and no psycho-acoustic compression) which delivered around 15kHz bandwith. It was also the standard for digital Sound-In-Syncs stereo audio used for composite contribution backhauls in Europe. 15kHz stereo was deemed "good enough" for TV ISTR, as it pretty well matched the quality of FM Stereo radio?

(In fact subjectively NICAM 728 often sounds better than 192kbps and 256kbps MPEG Layer 2 that we have for digital SD TV here. When listening to live classical stuff like the Proms, NICAM often used to sound cleaner and less "processed" to me - even though the MP2 stuff is probably 48kHz/16 bit...)

384 kbps results in an upper frequency limit of around 15 kHz, comparable to the range for analog TV.
And that's a hard limit, not the rolling off limit like in analog FM, right?

448 kbps results in an upper limit of about 20 kHz, comparable to CD. Eventually the data rate for DTV was allowed to include 448, but no one has ever required it to be changed.
I'm not sure that frequency response is the only effect. My hearing drops off quickly above 17 kHz but shows on my NBC affiliate don't have the full directional surround sound effect that 5.1 does on the other stations. Of course there could be other things involved (affiliates are known for screwing up their sound) and I'm willing to admit that I'm fooling myself but it seems like there's no reason that HDTV shouldn't have sound as good as a DVD.

I can hear a difference between 448 kbps DD and 640 kbps DD+. I've done back and forth comparisons between DVDs and HD-DVDs I own and I was very surprised. The Universal theme has a "blurry" sound field on DVDs to me.

I'm not one of those people who are insulted when an HD disc doesn't have lossless sound. I can't even tell the difference between that and 640 kbps DD+ sound most of the time.

And that's a hard limit, not the rolling off limit like in analog FM, right?


There's a hard limit, but the reconstruction filter will provide a roll-off to inaudibility somewhere below the hard limit.

I'm not sure that frequency response is the only effect. My hearing drops off quickly above 17 kHz but shows on my NBC affiliate don't have the full directional surround sound effect that 5.1 does on the other stations. Of course there could be other things involved (affiliates are known for screwing up their sound) and I'm willing to admit that I'm fooling myself but it seems like there's no reason that HDTV shouldn't have sound as good as a DVD.
Perhaps your affiliate is upmixing the Lt/Rt into DD5.1 instead of taking the discrete channels from the feed. A lot of older equipment isn't capable of routing and switching more than 2 channels of audio, so upmixing the 2-channel surround is a cheap and easy way of turning on the DD5.1 light. The surround sound would suck compared to 6 discrete channels, but since most of the viewing audience using TV speakers will never know the difference, they can probably get away with it. The easiest way to tell is to mute or disconnect the center channel. If you still hear dialog, it's not real 5.1.

There's a hard limit, but the reconstruction filter will provide a roll-off to inaudibility somewhere below the hard limit.

Also this link (http://www.spannerworks.net/reference/10_1a.asp) link says DD at 384 kbps goes up to 18 kHz which means my ears shouldn't be able to tell much if any difference between the two bit rates, at least with frequency response.

The easiest way to tell is to mute or disconnect the center channel. If you still hear dialog, it's not real 5.1.

Then it's real 5.1. I disconnect the center channel during Sunday Night Football so I don't have to listen to Madden and friends. Their voices do get into the subwoofer however, but there's no trace of their voices once I turn that off.

Then it's real 5.1. I disconnect the center channel during Sunday Night Football so I don't have to listen to Madden and friends. Their voices do get into the subwoofer however, but there's no trace of their voices once I turn that off.
Nice. Try it the other way too, disconnect the L/R and surrounds and see if you get any music during normal NBC dramas. In general, music should only be in L/R, and anything in C indicates a non-discrete mix.