High & Low Symbol Rates Gambit

[zamar23]

I just red the fresh thread on 4:2:2 channels here, and someone mentioned registering a 4:2:2 encoded channel with as low symbol rate as 3038. I wonder if picture quality was good at these low rates? What would prompt a broadcaster to transmit a beautifully colored pic with low symbol rates, especially when reporting highly dynamic scenes like games?

Would you share guys, what was the lowest and highest symbol rate channel you were ever able to catch? Who was the broadcaster and on what sat? What was the modulation and FEC used?

Also, several Sat Guys complained about some receivers won't be able to either decode or write & play back low or high symbol rates channels? What was the receiver model, and why in your view it was incapable to tune in or decode such a rate? What's your theory behind it?

 

[Mr Tony]

I just red the fresh thread on 4:2:2 channels here, and someone mentioned registering a 4:2:2 encoded channel with as low symbol rate as 3038. I wonder if picture quality was good at these low rates? What would prompt a broadcaster to transmit a beautifully colored pic with low symbol rates, especially when reporting highly dynamic scenes like games?

unknown.....other than the fact that the same station has done both news and sports broadcasts in 4:2:2 using the same symbol rate

Would you share guys, what was the lowest and highest symbol rate channel you were ever able to catch? Who was the broadcaster and on what sat?

lowest 24/7...KFTL 1666 s/r on 72W...more common is 2170
lowest feed....dont remember the name but a 1000 s/r
highest s/r is 30000 for both feeds and 24/7...PBS on 125W and sports feeds on various sats...highest s/r period (no channels) there use to be one on 93W that was 45000 (or was it 45002)....no channels though

Also, several Sat Guys complained about some receivers won't be able to either decode or write & play back low or high symbol rates channels? What was the receiver model, and why in your view it was incapable to tune in or decode such a rate? What's your theory behind it?

I dont have any issues playing any feed on the azbox regardless if its low symbol rate (like 2170) or high like 30000. Only when recording to a hard drive attached to the usb port. If I hook a separate DVD recorder/HDD to it I can record just fine.

Some receivers blind scans wont pick up real well lower than 2000 and that is usually written in the specs. Will it possibly pick up lower on a blind scan? yes. My Pansat 1500 will grab KFTL with no issues and use to grab KCSG that was on 97W C-Band with a s/r of 1970. Coolsat will skip KFTL every time even on detail. It will grab 2170 s/r with no issues.

 

[zamar23]

Thanks Ice!

Very interesting. Did you notice that HD or advanced color broadcast pic quality would noticeably degrade with lower symbol rates? How lowering symbol rates reflected on quality of highly dynamic scenes like fast games?

I wonder if lowering the rates while adding 4:2:2 simply allows the broadcaster to maintain current bandwidth and keep costs down? But there should be seemingly different encoding technology in place that would allow to sharply decrease amount of motion data transmitted without degrading pic quality especially in dynamic scenes.

 

[skysurfer]

If you understand what 4:2:2 is compared to 4:2:0, I would think you have more data to be transmitted, not less so a symbol rate lowering wouldn't be beneficial unless you change the modulation or the FEC in order to lower the symbol rate yet increase the data rate.

lowest signal I've locked - 1000 SR - a network news service IFB transmission. highest SR I've locked is 45,000 - internet service. highest video SR I've locked is 32,362 and lowest video SR is probably like 1628 IIRC.

 

[zamar23]

Chroma Subsampling

This Wiki article explains what [ame="http://en.wikipedia.org/wiki/4:2:2"]Chroma subsampling - Wikipedia, the free encyclopedia@@AMEPARAM@@/wiki/File:Question_book-new.svg" class="image"><img alt="Question book-new.svg" src="http://upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png"@@AMEPARAM@@en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png[/ame] Chroma Subsampling techniques are, including 4:2:0 and 4:2:2.

"Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information than for luma information. In video, Luminance (luma) represents the brightness in an image (the "black and white" or achromatic portion of the image).

Chrominance (chroma for short), is the signal used in video systems to convey the color information of the picture, separately from the accompanying luma signal. Chrominance is usually represented as two color-difference components: U = B'–Y' (blue – luma) and V = R'–Y' (red – luma). Each of these difference components may have scale factors and offsets applied to them, as specified by the applicable video standard.

In composite video signals, the U and V signals modulate a color carrier signal, and the result is referred to as the chrominance signal; the phase and amplitude of this modulated predominance signal correspond approximately to the hue and saturation of the color. In digital-video and still-image colorspaces such as Y'CbCr, the luma and chrominance components are digital sample values. Separating RGB color signals into luma and chrominance allows the bandwidth of each to be determined separately. Typically, the chrominance bandwidth is reduced in analog composite video by reducing the bandwidth of a modulated color subcarrier, and in digital systems by chroma subsampling."


skysurfer

What were the channels with lowest and highest SR you mentioned?

I agree, merely symbol rate lowering wouldn't be beneficial, but using more advanced modulation like 8psk instead of QPSK and decreasing FEC (the amount of error correction data) by improving link quality (signal strength), its possible to increase signal bit rate while decreasing symbol rate, since the higher the modulation the more tones are used and more bits transmitted with each symbol. However, for highly dynamic scenes using only this technique may not be enough, requiring also more efficient codecs and video compression algorithms like H.264 variations allowing to decrease required number of bits to deliver the same video quality.

So, I assume its a combination of all known techniques that allows to decrease required symbol rate without affecting pic quality. Such signal may require however newer receivers to decode, which support newer modulations and incorporate newer codecs, unless more codecs can be added to the receiver, like in Linux STBs.

 

[zamar23]

Symbol Rate

Simple definition of the term Symbol Rate is given here:

"The symbol rate is the rate of state changes on a communications circuit. If a circuit can carry two tones per second, the circuit has a symbol rate of two. Circuits then use different modulation techniques to carry multiple bits per symbol. If the circuit is limited to two different tones, the first tone can represent a 0 and the second tone can represent a 1. In this circuit, the symbol rate is the same as the bit rate. If the circuit can carry four different tones, then the tones can be used to encode twice as many bits per symbol. In this circuit, the bit rate is now twice the symbol rate.

Using more tones allows more bits per second (bps) to be squeezed out of every symbol, but this also requires higher quality circuits. If the circuit is not high enough quality, the number of retransmissions will cause the circuit to be slower than with a lower number of tones. The choice of how many tones to use is determined by the modulation algorithm chosen. QPSK uses four tones, 8PSK uses eight tones. The use of 4 tones is standard in the satellite world. In the cable television world, the higher quality transmission medium enables 64QAM modulation to be the standard. Symbol Rate is abbreviated as SR. The symbol rate is also known as the baud rate."


QPSK (Quadrature Phase Shift Keying) is a phase modulation algorithm.

Phase modulation is a version of frequency modulation where the phase of the carrier wave is modulated to encode bits of digital information in each phase change. The "PSK" in QPSK refers to the use of Phased Shift Keying. Phased Shift Keying is a form of phase modulation which is accomplished by the use of a discrete number of states. QPSK refers to PSK with 4 states. With half that number of states, you will have BPSK (Binary Phased Shift Keying). With twice the number of states as QPSK, you will have 8PSK. The "Quad" in QPSK refers to four phases in which a carrier is sent in QPSK: 45, 135, 225, and 315 degrees. Because QPSK has 4 possible states, QPSK is able to encode two bits per symbol. QPSK is more tolerant of link degradation than 8PSK, but does not provide as much data capacity.

Phase Data

45 degrees Binary 00
135 degrees Binary 01
225 degrees Binary 11
315 degrees Binary 10


8PSK (8 Phase Shift Keying) is a phase modulation algorithm.

Phase modulation is a version of frequency modulation where the phase of the carrier wave is modulated to encode bits of digital information in each phase change. The "PSK" in 8PSK refers to the use of Phased Shift Keying. Phased Shift Keying is a form of phase modulation which is accomplished by the use of a discrete number of states. 8PSK refers to PSK with 8 sates. With half that number of states, you will have QPSK. With twice the number of states as 8PSK, you will have 16PSK. Because QPSK has 8 possible states 8PSK is able to encode three bits per symbol. 8PSK is less tolerant of link degradation than QPSK, but provides more data capacity."


TS Reader author also gives clear definition of basic satellite transmission terms, including Symbol Rate.

 

[Mr Tony]

Very interesting. Did you notice that HD or advanced color broadcast pic quality would noticeably degrade with lower symbol rates? How lowering symbol rates reflected on quality of highly dynamic scenes like fast games?

sports feeds in HD rarely use a symbol rate lower than 25000...The 3 "normal ones" are 26450 (and 26470), 29270 and 30000 and all usually look the same. The station that is originating the broadcast likes to "stick" with a specific s/r

Have there been sports feeds with symbol rate below 25000? yes
Can I remember one recently? no

news feeds I've seen in HD I have seen use 6111 as a symbol rate but since its usually a 5-10 minute segment they dont need much bandwidth.

 

[Mr Tony]

What were the channels with lowest and highest SR you mentioned?

looks like skysurfer posted the same hi and low as I did. 1000 was a feed and 45000 has no channels

 

[zamar23]

Anyone experienced problems with low or high bit rate sat channel recording or playback to a PVR? Was it recorded to a USB or LAN drive? How did the problem show up? What STB did you use, and what were the signal SR and modulation type or channel & sat? This info would be helpful to others when buying a new or used STB.

 

[skysurfer]

Have there been sports feeds with symbol rate below 25000? yes
Can I remember one recently? no

you don't watch TNT or TBS sports, I take it? They use just under 25000 SR.

Golf Channel HD backhauls use 13000 and can do that because they use H.264 video compression.

 

[Mr Tony]

Other than the baseball on TBS the answer would be no