ATSC Digital Audio Quality, Technology, Issues

[holl_ands]

Numerous stations in U.S. have been (incorrectly) configured when using a TWO-CHANNEL
Splicer to insert local newsbreaks and adverts. [Google "missing center channel"]

The station's Dolby Digital Decoder outputs L,R,C,LS,RS&SW as well as a Lt and Rt (total) Stereo feed.
Some stations are (incorrectly) using the L+R outputs when they SHOULD be using the Lt+Rt outputs,
resulting in a "Missing Center" (or greatly subdued). Center carries not only MOST of the sound energy,
but ALSO has a lot of Bass energy, which MIGHT be very faint in the separate L&R channels if the
sound engineer primarily mixed it into the "common" Center channel.

BTW: Lt+Rt (per specs) does NOT include the SW channel energy...which can cause a loss of Bass
if the station passes either L+R or Lt+Rt through their TWO-CHANNEL splicer and when switching back
to the main program, "forget" to bypass the splicer....you'll ALWAYS hear Stereo...with no SW channel.

My Pioneer AVR has a "Enhanced Dialog" setting, which figures out how to enhance the Center
channel after forcing the L and R signals to be "more coherent...i.e. in-phase". This dramatically
improves both the "Missing Center" and "Missing Bass" problems...but only in Stereo mode....huh???

A third cause of reduced Bass and ill-defined Center channel is the Circle Surround Encoder being
used by most sports channels on their L+R channels to provide an "enhanced user experience".
I have NOT IDEA what that is SUPPOSED to do when concatenated into a DD5.1 transmission
and reproduced into separate speakers, without benefit of going through a Surround Decoder......
It appears to be somewhat incompatible with not only my HDTV's built-in "Matrix Surround" decoder,
but also ALL of the many different synthetic surround modes in my Pioneer AVR....
http://www.srslabs.com/uploadedFiles...20Decoding.pdf
http://www.5dot1.com/articles/circle_surround.html

[holl_ands]

Originally Posted by chengbin

@JamesK

I know exactly what you're talking about (I boost treble on my computer speakers), but the difference is large enough that it can't be that.

ATSC does not have better sound quality than CD. ATSC's audio is 6 channel AC3 compressed @ 448Kbps (or 384Kbps?) @ 48KHz. CD is uncompressed @ 1411Kbps for 2 channels @ 44.1KHz. AC3 is technically better being 48KHz, translating into 24KHz of usable frequency spectrum, rather than 22KHz of CD. But CD's *uncompressed* stereo, so it doesn't get better than this for 2 channel sound @ 44.1KHz. Therefore CD is still better than ATSC.

There are many people who prefer DD5.1 to CD's....they take advantage of not only
the larger dynamic range, but also have a SUBWOOFER and SURROUND channels....
Although OTA ATSC suffers from a host of problems in the SOURCE material (GIGO),
I (and many others) much prefer the SOUND of DD5.1 Music DVD's (bonus.....moving pictures)
to the same material on CD's......

CD's are 16-bit at 44 KHz sampling for 96 dB SNR and 22 kHz max bandwidth.
DD5.1 is (up to) 24-bit at 48 kHz sampling for 144 dB SNR (actual 110+ dB) and 24 kHz max.

When was the last time YOU switched to the 2.3 Mbps (24-bit/48 kHz) PCM Stereo track on a DVD/BD
instead of the compressed 448-640 kbps DD5.1 Surround Track because the sound was "better"?????
[BTW: DD5.1 data compression is achieved by doing a frequency transform and throwing away the
extra data bits that convey no useful information....it does NOT compress the dynamic range.]

I prefer DTS to DD5.1 on DVDs.....and lossless DVD-Audio & SACD are BEST....and are in Surround....
And I'm NEVER going back to (hiss, click, pop) Vinyl....like some retro-audiophiles are doing.....

But ultimately the recording technology is NOT the determining factor...it's how many
compromises were made when slapping together the signal PRIOR to the recording....

[jgconnor]

Originally Posted by chengbin

The ATSC volume is noticeably lower than NTSC on my LG speakers for most channels.

Probably due to volume compression where they have effectively reduced the dynamic range to accommodate lo-fi TV speakers and mask the inherent analogue noise.

In my set up the OTA DD audio sounds infinitely better than OTA analogue.

[GeorgeMx]

Originally Posted by HWP

On my TV...
...I don't have a home theatre but I'd be willing to bet it is not coming in in Dolby quality....

All audio on ATSC is Dolby format with one or more channels so the issue can't be transmission technology. What leads you to the conclusion that "it is not coming in in Dolby quality"? What do you mean by the term "Dolby quality"?

[HWP]

Sorry about that.

I don't know the lingo when it comes to audio. I just have whatever sound comes out of the speakers on my TV.

Yesterday, Bentoronto asked...
[Does (or can?) their TV music feed include HD-FM as on the FM band at 94.5-1 and 94.5-2? I ask this because no one has explained to my grasp about the fidelity standards of these language/music transmissions for music except to repeat "hey, it's digital so it has to be perrrrrfect." HD-FM has its limitations and I wonder how they compare to digital subchannels?]

When I went to 17.3 Think Bright WNED and listened to the radio simulcasts, my sense ws that the sound was not FM quality or at least not better. There was a bit of cutting out. Keep in mind I was only checking out the channels and not really listening to it for any length of time.

To be honest, I don't even know what "high definition radio" means. Digital, I am sure. But five speakers, two speakers, I have no idea. I assumed that the TV stations were not sending out any more than a regular stereo signal, in digital, of course, over the subchannel.

I'd love to read an "intro to high definition radio" in the appropriate thread.

Oh yeah. I also don't know what Dolby means.

[tvlurker]

Originally Posted by jgconnor

Probably due to volume compression where they have effectively reduced the dynamic range to accommodate lo-fi TV speakers and mask the inherent analogue noise.

In my set up the OTA DD audio sounds infinitely better than OTA analogue.

What inherent analog noise are you talking about in analog audio FM transmission?

[JamesK]

^^^^
The front end amplifiers in receivers generate a lot of noise and is the dominant cause of noise at VHF frequencies. In FM, the signal to noise ratio depends on how strong the signal is. With a strong signal, there'll be little, with a weak signal, a lot. However, all analog transmission methods experience noise. With digital systems, the only source of noise is quantitizing error, due to discrete steps rather than continuous function in the codecs. This means your signal to noise ratio is determined entirely by the number of bits. In the case of CDs, 16 bits results in 96 dB s/n ratio. Someone else mentioned ATSC uses 24 bits, which results in 144 dB s/n ratio (ignoring noise caused by compression). Also, due to using 25 kHz deviation, TV audio is noisier than FM broadcast, which uses 75 kHz deviation.

[Schmerpy]

Actually, when watching a concert on Bluray or DVD, I ALWAYS choose in this order:

1. 2 channel PCM sound format (i.e., CD quality);
2. Dolby TrueHD or DTS-HD;
3. DTS;
4. DD.

From where I'm sitting, CD quality ABSOLUTELY SMOKES Dolby Digital. Of course, your amplifier and speakers actually have to be capable of resolving this difference, and I would venture to say that 99% of people out there do not have equipment that would be truely up to this task.

I challenge you to ask any audiophile what has a better sound quality when properly mastered: DD 5.1 or CD. Most will be stunned that the question was even asked. DD is lossy compression and the loss is SIGNIFICANT. Only the new HD sound formats like Dolby TrueHD, which are lossless formats, can compete with CD. The various SNRs is irrelevant because humans cannot hear that difference.

[tvlurker]

Originally Posted by JamesK

^^^^
The front end amplifiers in receivers generate a lot of noise and is the dominant cause of noise at VHF frequencies. In FM, the signal to noise ratio depends on how strong the signal is. With a strong signal, there'll be little, with a weak signal, a lot. However, all analog transmission methods experience noise. With digital systems, the only source of noise is quantitizing error, due to discrete steps rather than continuous function in the codecs. This means your signal to noise ratio is determined entirely by the number of bits. In the case of CDs, 16 bits results in 96 dB s/n ratio. Someone else mentioned ATSC uses 24 bits, which results in 144 dB s/n ratio (ignoring noise caused by compression). Also, due to using 25 kHz deviation, TV audio is noisier than FM broadcast, which uses 75 kHz deviation.

Thanks for the refresher in modulation theory. You're right, the SNR for an FM modulation scheme would be lower than the digital ones, especially for lower deviations.

[Foxenhimr]

Hi Folks,

Hoping it's appropriate to post this question here.

I am in the *very* early stages of figuring all this OTA stuff out, and have a question : Do you get 5.1 surround sound with an HD OTA broadcast ?

Thanks !

[Jase88]

^^^^
Yes, ATSC (the digital standard used in North American digital over-the-air) supports 5.1 if the broadcaster is sending it out.

[j0dest3r]

Yes you do. CBC hockey game channel 5.1 shows DD+ with the crowd in the back speakers and the announcers through center channel.

[Foxenhimr]

Total OTA newbie here. Had antenna installed several days ago in south Ottawa, and just beginning to configure things. Simple question: can 5.1 audio be transmitted OTA, or just stereo ?

[MaxHeadroom]

Congrats on the move to OTA! Welcome to the club.

If your tuner supports it, and it should, 5.1 is available in Ottawa. Not every program is broadcast in 5.1, though.

[57]

As mentioned above, DD5.1 is available OTA, however, some programming is not DD5.1 and you need to make the appropriate connections as outlined in the following FAQ:

http://www.digitalhome.ca/forum/showthread.php?t=17870