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Author Topic: A digital question  (Read 5170 times)

hargerst

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A digital question
« on: February 22, 2006, 01:09:59 PM »

Last year, I decided to treat myself to a 44" LCD HDTV digital TV, and added some HDTV channels to my Dish Network subscription.  The picture on the HDTV channels is superb, and I'm going back and watching all my old DVDs, which are, for the most part, wonderful.

BUT, on some movies, when you're watching a very dark scene, you don't see smooth blacks and greys. You see dark, large blobs of purple, green, and grey. Huge square chunks of them, with straight, boxey edges.

Now, I think this is because they're running out of bits or resolution at the dark end of the video spectrum.  It's pretty ugly looking. It got me to wondering if there's the same thing happening in the audio world when we start running out of bits or resolution.

Any thoughts?

It would explain some of people's unhappiness with digital sound.
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Harvey "Is that the right note?" Gerst
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scott volthause

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Re: A digital question
« Reply #1 on: February 22, 2006, 01:21:37 PM »

That's the mpeg compression artifacts on the DVD. In order to reduce the movie size to fit on the DVD along with all the extras, they have to compress the video to fit. It's pretty much the same with jpeg image compression, you lose all the fine gradients in order to have a decent file size.

So you could say that an mp3 is like your DVD. It's a compromise.

I wouldn't say that 24 bit 48kHz digital audio suffers from that so much.
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Fibes

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Re: A digital question
« Reply #2 on: February 22, 2006, 01:28:43 PM »

Harvey,

It's dither.

A different thing in the video realm but evil nonetheless.

Digital cable does the same thing. Screw "digital quality."
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spcbrown

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Re: A digital question
« Reply #3 on: February 22, 2006, 02:50:28 PM »

I would add one thing and please correct me if I'm wrong, but LCD technology isn't the best either. I think either DLP or Plasma offer the blacker black and one or the other are the ones that win the shootouts in direct side by side competitions amongst LCD, DLP, & Plasma. I read a lot of Sound & Vision among other things.
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Adam "The Thread Jacker" Brown

SirDonut

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Re: A digital question
« Reply #4 on: February 23, 2006, 08:29:56 AM »

spcbrown wrote on Wed, 22 February 2006 19:50

I would add one thing and please correct me if I'm wrong, but LCD technology isn't the best either. I think either DLP or Plasma offer the blacker black and one or the other are the ones that win the shootouts in direct side by side competitions amongst LCD, DLP, & Plasma. I read a lot of Sound & Vision among other things.


It all depends on the model/manufacturer...I wouldnt make generalizations like that. I think the tube HDTVs look the best for the price. They cost at least 1/3 as much as their LCD/Plasma counterparts. Unfortunately manufacturers only make them up around 30 inches I believe as when they get any bigger they get super cumbersome.

Unfortunately it's really hard to shop for HDTVs as generally the salesmen are morons and the stores dont have true HD fed to a lot of the HDTVs. But hey, isn't that just like going to banjo center?
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hargerst

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Re: A digital question
« Reply #5 on: February 23, 2006, 10:48:22 AM »

When I went shopping, I almost bought the Sony 42" Plasma TV, but the Zenith 44" LCD was closing out at $1,600 and the HD picture was spectacular.  On HD sources (and DVD's), it's a great picture.

But those blotchy black squares on some regular sources (any scene that has the dialog "Watch your step - I'll find the lights.") are really annoying.
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Harvey "Is that the right note?" Gerst
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Tidewater

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Re: A digital question
« Reply #6 on: February 23, 2006, 04:05:15 PM »

Notice that the HD example channels don't do that, like the stadium scene, where you can read the numbers on the seats..

I hate the splotches moving around.

Compression sucks. Dither, withers.


M
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spcbrown

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Re: A digital question
« Reply #7 on: February 24, 2006, 03:49:04 PM »

I was at Fry's just the other day and checked out all LCD, DLP, and Plasma TVs they had and indeed the first LCD looked great...it was the vivid color and bright and clear picture that got my attention which is what LCDs do best. The DLP and Plasmas had an obviously darker picture and didn't reveal color aswell as the LCD but the DLP and Plasma had better...call it definition to the picture. It is as usual...a compromise...ya get the (1)price ya want...(2)screen size...(3)portrail of living and vivid colors...(4)exacting picture definition. However...you can only have two of the four combined.
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Adam "The Thread Jacker" Brown

Steve Brady

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Re: A digital question
« Reply #8 on: March 11, 2006, 12:18:19 PM »

Harvey,

You are absolutely correct about the bits/bytes issue. The digital world is limited to the number of bits/bytes available, where as the analog world is Infinity.  Darker colors have larger wavelengths, lighter colors have smaller wavelengths.  Larger modulations require more bits/bytes, which is why the dark colors are splotchy on your screen.

Same analogy goes for wavelengths of sound - the lower you get to 20Hz, the larger the wavelength thus the larger modulation requires more bits/bytes which is one of the reasons why digital can't reproduce the great deep bass in detail as analog.

Think about this: if you break down the tones just between notes C & D (beyond half steps) in the analog world, you can keep dividing the steps between the notes C & D smaller and smaller, and keep doing so until Infinity.  Our ears CAN hear those slight nuances between the steps in analog just as it can hear slight nuances in space & time.  It's like trying to find the exact value of 1/2 inch on a ruler.  You can't find exactly 1/2" in the analog world, because you can always go smaller - the smaller you go, the more accurate your measurement of 1/2" is.  Digital can only divide those steps between notes C & D down just so far because of the bit/byte limitation - just as it's limited to how small it can calculate the exact value of 1/2 inch on a large ruler, therefore Digital can only locate the closet value number it can given the number of bits/bytes dedicated.  

Big picture: not only does digital have to dedicate bit/bytes for note (sound) reproduction, but also for spatial reproduction.  This is why digital can never duplicate analog.  It can only provide/calculate the closest value it can (because of bit/byte limitations) and therfore it cannot provide accurate reproduction.  If you're with me so far, what this means is a supercomputer cannot provide enough bits/bytes and binary code to accurately reproduce the true world of analog Infinity.  

Here's another view in the words of someone from my hometown:

"The instant you digitize a signal, you destroy the phase-angle relationship between the high frequencies and the lows. That’s why you can’t make a decent chorus with a digital delay unit. Phase-angle distortion has been with us since the day 3M introduced their incredibly expensive, 15kHz digital-recording deck. I still remember the famous quote from their marketing department: “There is an introduction of phase-angle distortion, but the human ear can’t hear it".

"I find that so hysterical because the human ear can hear things we can’t measure yet. And the ear does use phase-angle information to determine the location sounds originate from, and the space within which you’re standing when you hear those sounds. Simply put, that’s what tells you, “Oh, that sound came from over there.” The end result is that digitized music destroys the spatial characteristics of the music....

"... The two advantages of digital are that it’s cheap, and it gives you lots of features. As far as sound quality goes, digital is always worse."

--Tom Scholz, - Guitar Player Magazine, May 2003
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wwittman

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Re: A digital question
« Reply #9 on: March 11, 2006, 06:19:02 PM »

It's the same reason why in an analogue recording you hear the depth and air around things and in a digital one, it seems flatter and shallower.
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William Wittman
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Steve Brady

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Re: A digital question
« Reply #10 on: March 11, 2006, 06:54:47 PM »

wwittman wrote on Sat, 11 March 2006 23:19

It's the same reason why in an analogue recording you hear the depth and air around things and in a digital one, it seems flatter and shallower.


Yes Sir William - you are precisely correct.

Interestingly, some buds of mine were diehard digital freaks.  I had them over for a sound test.  The heart of my stereo is an all tube McIntosh preamp & all tube McIntosh power amp.  I compared a first class stamping of an album vs. the same album on CD and flipped between the Phono and CD while both were playing simultaneously.  The guys jaws dropped at how realistic the album sounded in comparison to the CD (and it was thru a crappy BSR turntable I bought at Montgomery Wards in the 1970s!).  The music from the CD didn't possess the same "spaciousness" and depth in comparison to the album.  Also, the cymbals on the CD sounded completely different and more brash and the bass was much less defined (thinner).  The album's cymbals were crisp, realistic and much shinier and the bass was so full that it literally rattled the windows.

I can understand the argument that digital may be more affordable and easier to manipulate, but for folks to say digital sounds better than analog is absurd.  It's mathematically impossible for digital to sound as good or better than analog.

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Steve Brady

garret

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Re: A digital question
« Reply #11 on: March 11, 2006, 11:06:51 PM »

I think the key point is that DVD video has extremely lossy MPEG2 data compression.   Typical DVD data rates are around 5 Mbits/second.   That sounds like a lot, but raw video of the same size (720 x 480 pixels) and frame rate (30 frames/second) would be 248 Mbits/second.   So we're talking a compression ratio of 50:1.  (I.e., they throw out 98% of the data, and keep just 2%).

To make a better analogy to digital audio, compare DVD to mp3 audio compression...

Raw CD-quality stereo audio is 1411 kbps. 50:1 compression would be 28kbps.  And to think I can't stand listening to mp3s at less than 128kbps.  Smile

Standard DVD's are never going to look good on a 42" screen...  some say they don't look good on any screen bigger than 20".  Optical laserdiscs (from 1978!) are still is the best format, besides film.

There are several competing standards for high definition DVD under development.   Last I saw though, HD DVD format was going to be around 28 Mbps.  So 10:1 compression.   That should be much better, but it'll still not be enough to please the "film is best" crowd.

So I guess my point is that you can't say that DVD looks bad just because it's digital.   It looks bad because it's digital and it's horribly overcompressed.  
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wwittman

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Re: A digital question
« Reply #12 on: March 11, 2006, 11:38:00 PM »

call me not intellectually curious, but I don't care WHY digital doesn't sound or look as good, as much as I care THAT digital doesn;t sound or look as good,

I work in the fomrats that I have to.
but that doesn't mean I need to pretend they sound as good as the formats I used to work in.
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William Wittman
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Steve Brady

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Re: A digital question
« Reply #13 on: March 12, 2006, 08:27:13 AM »

garretg wrote on Sun, 12 March 2006 04:06


So I guess my point is that you can't say that DVD looks bad just because it's digital.   It looks bad because it's digital and it's horribly overcompressed.  



Digital will never be able duplicate analog due to its bit/byte limitation - it defies the law of physics.  Digital will never be able to dedicate enough bits/bytes to exactly duplicate the saturation, tint/shade of hue of a color that your eye sees in the real world.  Digital can only approximate because of bit/byte limitation.  Digital pictures appear "sharper" because the bit/byte limitations can't duplicate the detail of natural smoothness...and it never will.

In the case of your CD 128kpbs sound quality, that's the bare minimum of bit/bytes that gets the digital format to sound acceptable.  But even if you increased the bit/byte level by 1,000x, it still will not accurately reflect what your ear truly hears on magnetic tape - or in real life.  

One more thing: Digital creates odd-order distortion and phase angle destruction - and our brains are programmed for even-order distortion: Analog.

Now, magnetic tape doesn't reproduce sound exactly as we heard it the first time either, but it's light years ahead of where digital is.  Digital is a huge step backwards in sound and video reproduction, but as Tom Scholz says, digital is cheap, it's easily manipulable, and it adds to corporate bottom line.


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Steve Brady

Steve Brady

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Re: A digital question
« Reply #14 on: March 12, 2006, 10:26:45 AM »

wwittman wrote on Sat, 11 March 2006 23:19

It's the same reason why in an analogue recording you hear the depth and air around things and in a digital one, it seems flatter and shallower.


William,

Speaking of air makes me think of compression and the use of compressors.  Have you or Harvey done a 'Everything You Want To Know About Compressors But Were Afraid To Ask' type of post?

Correct and precise use of compression still remains a mystery to me (and probably MANY others as well)...

Thank you in advance...

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