Winegard-FV-30BB HDTV Antenna

[DarkHumour]

Think of how bad music sounds when transmitted over a land line phone and especially over a cell phone. Again, the richness of the signal (audio here) is being cut down in order to cram more voice "channels" into the same medium.

That's why the arguments I see on commercials for cable or satellite - we have MORE HDTV channels translates to we've crammed more into the same bandwidth by compromising the quality of them...  Heh, analogy just came to mind where a candy company could claim "we have more M&Ms in the bag now" - either because they are physically smaller or they smashed with a hammer before sealing the wrapper.

DarkHumour

[Walter Mitty]

Uh, that's perfectly OK, please keep proofreading the garbage I write. 

I see exactly what you're saying. You do a "brain fart" when you stumble across malapropisms in subject matter that you are just learning. A more technically experienced reader (in that discipline) will not notice the error.

Another way to understand the issue is like this:

Over the air (or *broadcast*) TV is closest to the source. It is the purest form of the digital image that you will ever see. The only way to see any "purer" a signal would be to work inside the TV studio.

Satellite and cable transmission always consists of re-encoding this signal to make it take up less bandwidth - which translates directly to more channels that the carrier can sell to consumers, IE, it's a revenue and cost thing. So television over cable has been "altered" - messed with. Usually to degrade the quality so it can be squeezed into fewer megahertz of bandwidth.

Think of how bad music sounds when transmitted over a land line phone and especially over a cell phone. Again, the richness of the signal (audio here) is being cut down in order to cram more voice "channels" into the same medium.

In dealing with informations systems in conjunction with databases, I've used the term "upstream" to describe closer to the source.  And yeah, "downstream" usually means "degraded", except maybe when the processing got rid of irrelevant parts of the data. 

My impression is that "messing with the singal"  has real different implications whether we're talking analog or digital.  If you push music through a land line, what it generally means is that you lose all the highs and lows.

[The Gorn]

Most of the degradation is digital and is engineered with intent. My understanding (I have basic communications theory classwork and experience) is that many voice telephone signals are multiplexed onto one wire or optical fiber and the high frequency components are stripped out so that more signals can be transmitted over a given carrier.

Say most of us can hear up to 10-12khz and frequencies up to that limit are picked up and transmitted with reasonable fidelity by most phone equipment.  If the high frequency components of an audio signal are stripped, say anything about 8 KHZ, then the engineer whose job it is to modulate that frequency onto a carrier wave just saved 33% or so in bandwidth.

Exactly the same principle applies to TV. The video signal's upper frequencies are dropped (in a MPEG movie compression sense, which is still "real" bandwidth). The direct result of this is that small visual details are lost, and the colors become blocky and quantized (you see steps in colors instead of smooth colors.)

Let's take an example.

An AM radio signal consists of an audio signal which is literally multiplied by a carrier signal which is a continuous sine wave of, say, 1 megahertz. The result of this multiplication is the radio signal that stations broadcast.

The audio signal's "footprint" in the AM radio band consists of components equal to the audio signal's topmost frequency components, and on both sides of the nominal carrier signal's signal.

So a 1 MHZ carrier that carries music and voice will result in 1 x the audio spectrum's "width" or footprint on either side of the 1 MHZ. So if the audio ranges to 12 KHZ then the radio signal that represents that audio will be 24 KHZ wide. (Digression: each excursion of the signal in the direction "up" and "down" away from the carrier frequency is called the "sideband." AM signals have two sidebands.)

That means specifically that another different radio station needs to broadcast at a frequency at least (bare minimum) no less than 12 KHZ more, or 12 KHZ less, than 1 MHZ. If the second station in a radius of reception comes any closer in frequency to our example 1 MHZ transmitter than 12 khz, then interference between the two stations will inevitably result. A station that broadcast with a carrier signal based at either 1.012 MHZ or 9.88 MHZ would be exactly at the borderline of interfering with the first station in our example. A nearby station broadcasting at, say, 1.01 MHZ would definitely be interfering.

IMPORTANT note: audio engineers at every AM radio station can and do filter ALL components of their broadcasted audio which exceeds a certain frequency (in our example case 12 KHZ.) If they did not, then the guidelines for spacing radio stations on the dial would be variable.

This is the specific reason why and how radio stations can interfere with each other.  And this is exactly what the FCC tries to do in assigning frequencies and maximum powers and locations to radio stations. This is what specifically lead to the FCC being created.

So this is exactly how radio signals take up "spectrum room". This is where economic costs factor in with a private carrier medium like microwave links, satellite TV, or cable TV. The exact same principles of taking up spectrum room apply to video.

The AM example is analog in nature. Exactly the same principles apply to digital information. Because at some point all the digital signals become  a single analog signal that moves over a cable or over a satellite radio link.

Again, the loss of high frequency signal components - the gold standard of "quality" in either audio or video - is engineered, not incidental, for economic benefit.

A broadcast/over the air TV signal has a VERY wide "footprint" in the radio spectrum that is reserved for it. So the picture can be crystal clear and very detailed. The same signal may only be allotted half or less of that bandwidth via cable or satellite.

[Walter Mitty]

Did you mean "specifically led to the FCC being created"?  Now I'm just being a PITA.

 

[The Gorn]

Where's that freaking AP Style Guide when I need it!!!!???

Point noted.

[Walter Mitty]

Most of the degradation is digital and is engineered with intent. My understanding (I have basic communications theory classwork and experience) is that many voice telephone signals are multiplexed onto one wire or optical fiber and the high frequency components are stripped out so that more signals can be transmitted over a given carrier.

I've got very limited background in this area.  From what I've read, the maximum fidelity that can be passed by a digital encoding scheme varies according to the number of bits used to encode each second of signal.  If you have the additional requirement that transmission be real time, that ends up translating into  bandwidth.  And the real time requirement is definitely there when it comes to telephone conversation.

Also from reading,  Ma Bell was exploring digital transmission in the 1950s long before the technology would have made that practical.  At that time, the big innovation the public was seeing was direct distance dialing.  And the worst offender regarding unintentional signal degradation (as opposed to engineered) was the local switch.  Not the local lines or the trunk lines. 

The upper limit on high frequency you have to pass is real different depending on whether you want to pass conversation quality voice or concert hall quality music.  As Ma Bell switched over from unplanned degradation to engineered degradation,  they did a lot of studies about what's really needed to make phone conversations viable.

[Walter Mitty]

This is ultimate trivia...  While exploring digitized sound, one of the first songs Ma Bell digitized was "Daisy Bell"  (better known as "Bicycle built for two").  There was a reference to this in 2001 A Space Odyssey .  As HAL begins to lose his mind,  he sings Daisy Bell for Dave.


http://www.youtube.com/watch?v=OuEN5TjYRCE&feature=related
http://www.youtube.com/watch?v=UGsfwhb4-bQ&feature=related

[The Gorn]

I've got very limited background in this area.  From what I've read, the maximum fidelity that can be passed by a digital encoding scheme varies according to the number of bits used to encode each second of signal.  If you have the additional requirement that transmission be real time, that ends up translating into  bandwidth.  And the real time requirement is definitely there when it comes to telephone conversation.

You've got pieces of the whole puzzle in that statement.

Yes, the fidelity is partially governed by the number of bits that are used to encode the audio waveform. But mostly, fidelity is governed by the sampling rate as well as by the kind of data compression that takes place at later points in the processing. The sampling rate needs to be high enough to reproduce the data at the other end faithfully. And the compression may be responsible for significant degradation of the signal.

Nyquist criteria - the sampling rate has to be 2x the data content. A 5 KHZ voice waveform needs to be digitized with a 10 KHZ sample rate. (Actually it is called the Nyquist-Shannon Sampling Theorem.)

Sound is digitized by passing audio waveform data (the stuff that feeds, say, a speaker) through an "A to D" or analog to digital device. The voltage level is transformed into a bit pattern that is generally a scaled equivalent of the sound. The data is sampled, literally, read off of the 16 or 32 bits of output of the A-to-D at regular intervals. On a CD player this is 22 KHZ, I think.

Then, the fact that the "data words" that represent the audio follow certain laws of physics is used to compress that data in a "lossy" way, using what is called a discrete cosine transformation (DCT.) I am clueless about the exact mechanism, but basically, compression in a lossy way is what results in MP3 files that are *much* smaller than WAV files, the latter which contains a literal series of uncompressed data words representing the audio waveform and is huge. What a MP3 file contains is grey goo that a decompression program can convert back into waveform data.

Finally, when uncompressed by undoing the DCT, the digital data is played back to a human by passing the data words into a Digital to Analog converter. A data word of 6F00 becomes, for instance, 1.75 volts.

Very high lossy compression is part of what results in loss of fidelity. Very high compression, of course, makes the data relatively small.

It's actually THAT "truncation" of the video signal that results in relatively poor satellite and cable video quality. MPEG is used for satellite and cable.

It's exactly like JPEG. Surely you have seen a blocky JPEG, compressed so it's small. Same idea.

[The Gorn]

The upper limit on high frequency you have to pass is real different depending on whether you want to pass conversation quality voice or concert hall quality music.  As Ma Bell switched over from unplanned degradation to engineered degradation,  they did a lot of studies about what's really needed to make phone conversations viable.

Initially, 50+ years ago, individual copper wire pairs carried each phone conversation. The call could have all the fidelity it wanted. Maybe cross talk between pairs was a problem but the bandwidth allowed over a copper pair was unbounded.

The motivation to digitize conversations is born from wanting to have each copper wire pair carry 2, 3, or more conversations at once.

One way to do this would be to treat each copper pair as a private "radio frequency band" and push modulated carriers over the wire. Sort of a microcosm of the broadcast spectrum except restricted to one conductor pair. So maybe you'd have 10 people talking at once over that pair.

For many reasons this was/is impractical - equipment cost, crosstalk generated by high frequencies.

The other way to do this would be to treat the copper pair as a LAN, and push digital traffic over it that consists of many encoded voice conversations at once.

So if the "LAN" can carry 1 megabit, then you need to compress all of those voice conversations and turn them into a digital stream to fill up the 1 megabit of bandwidth (network speed.)

Today's phone systems really look and act like huge LANs. Just using far different electrical and data standards than Ethernet.

[The Gorn]

And the irony - with that specific knowledge, I still can't buy a good engineering job in this m**** f****ing local area.   

[DarkHumour]

And the irony - with that specific knowledge, I still can't buy a good engineering job in this m**** f****ing local area.   

Is Telarc still in Cincinatti ?

The irony of having faster computer processing, multitrack channels, 88, 96 and above sampling rates, and 24 bit dynamic range is that sadly with the popularity of MP3s they now engineer master tapes to a low fidelity sh*tty lossy format.

I haven't tried this yet but I wanted to rip a song to .wav.  Copy it and convert the copy to MP3 then back to .wav and do a differential between the original wav and the mp3 to find what was lost in conversion.

DarkHumour


 

[The Gorn]

Yeah, modern computer processing speeds allow the mediocritization of media. Before computers, all media was analog format, and for audio, it was generally much better - for recorded music, and even for phone calls.

[Walter Mitty]

And the irony - with that specific knowledge, I still can't buy a good engineering job in this m**** f****ing local area.   

What kind of engineering jobs use this kind of knowledge and related skills?  Who gets those jobs?

[Richardk]

There is a design floating around the internet for a DIY HD antenna made out of old coat hangers and scrap wood. I may build one for a second TV in the shed or the garage.

I built one of those and it doubled the number of stations that I could pick up. The downside is that it's not very pretty.

It's also quite directional, so use a site like www.tvfool.com to locate your towers. Another one is http://www.antennapoint.com

Finally note the band, UHF or VHF. One antenna style does not work across all frequencies.

[benali72]

I built one of the DIY antennas out of wood and coat hangers, and I've been using it now for 9 months in my living room. Works great.

I also bought the DB2 Antenna and have directly compared the two. I've found that their performance is nearly identical. One hint, though. If you build your own antenna, remember that Antenna connections are very delicate.... a slightly tighter screw can give you much better reception. So take due care when building your own.

Coat Hanger Antenna -- just search on "coat hanger antenna" at Youtube.

DB2 Antenna at Amazon -- http://www.amazon.com/Antennas-Direct-DB2-Directional-Antenna/dp/B000EHUE7I/ref=sr_1_1?ie=UTF8&qid=1317592679&sr=8-1