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Iv got the jitters about all this...

Discussion in 'Blu-ray & DVD Players & Recorders' started by Brad_Porter, Aug 9, 2002.

  1. Brad_Porter

    Brad_Porter
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    Right - thick boy here.

    Can someone explain to me in lay-mans terms the meaning of the below words, that are usually associated with DVD players in reviews.

    You can be as techincal as possible (Steady Nic :) ) but please start off with an idiots guide so I can 'get into it'.

    Video
    -------
    1. Jitter
    2. Inherent signal to noise ratio
    3. Chroma crosstalk
    4. Chroma AM/PM
    5. Frequency response at 5.8MHz

    Audio
    -------
    6. Digital deviation

    As always, thanks for the education.
     
  2. Nic Rhodes

    Nic Rhodes
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    I'm on holiday;)
     
  3. Brad_Porter

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    Are you contactable whilst on Holiday? I have a question to ask you. :D
     
  4. Jase

    Jase
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  5. lmccauley

    lmccauley
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    We know you won't be able to resist posting a 5,000 word answer for long... :D
     
  6. Brad_Porter

    Brad_Porter
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    Thanks Jase.

    Ill have a butchers.
     
  7. Jase

    Jase
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    To be honest Digital Deviation is the one that´s got me stumped.:( For example the Toshiba SD210 has a figure of 185 PS, the Arcam DV27 has 350.9. Does that make the Toshiba better than the Arcam for CD playback?:confused:

    I´d like to know if that applies to their analogue outs or the digital outs??
     
  8. Nic Rhodes

    Nic Rhodes
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    Dooh :blush:
     
  9. Nic Rhodes

    Nic Rhodes
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    All right then :D

    Mostly pilfered from elsewhere, saved time

    Jitter
    Quick fluctuations in some aspect of a signal such as amplitude or frequency resulting in a signal that is not stable and an output (video image or audio sound) that is not stable. Jitter is a common problem with CD players and other digital media. There are a number of "jitter reducing" components on the market which seek to eliminate most or all of the jitter in a digital signal. Jitter is caused most often by tiny fluctuations in disc size or spin rate compared to the constant clock speed (or problems with the clock itself, although this is not as often the culprit of jitter). Jitter results in distortion of the end product audio or video signal. Jitter is also common in video resulting in decreased picture quality or a slight shaking of the image on screen.

    I have written extensively on this on this site

    S/N Ratio (Signal-to-Noise Ratio)
    Maximum output of an electronic device or recording medium compared to its noise floor or level of background noise. S/N ratios are measured in decibels (dB), and larger numbers are better. A S/N ratio of 100 dB means that the maximum signal output is 100 decibels above the noise floor, or the point at which the signal will be obscured by noise (low-level hum and other electrical interference that is part of the component).

    Digital media such as CDs and DVDs tend to have higher signal-to-noise ratios than analog media such as VHS tapes and audiocassettes. When comparing audio/video components, a higher S/N ratio is better (of course the difference between a high 100 dB number and a 105 dB is not a deciding factor as both figures are excellent and will cause no problems in ordinary listening).

    Chroma Crosstalk
    Artifact in the Chrominance channel due to deficiency of the Y/C separation in the decoder. It consists of parasitic colour patterns on high frequency luminance textures. E.g. the cross colour moiré pattern is coloured even if the source picture is not – this may be because of the beating of the luminance frequencies generated by say a tweed jacket, and the sub-carrier frequency (Chrominance). I am sure everyone will have seen this if the weatherman wears a tweed / stripped jacket on TV.

    Chroma AM/PM
    This is simply a measure of the amplitude and phase noise present in the colour signal.

    Frequency response at 5.8MHz
    A common measure of video signal path performance. Gain is plotted in decibels (dB) over a given frequency range (phase and delay can also be added). Tolerances of the frequency response are quoted for circuits in dB, this being the deviation from the ideal curve (flat). Many people call this frequency response, inaccurately, it is actually bandwidth.

    Digital deviation
    This is just a measure of jitter. It is the difference in time between the two digital signals, typically measured in ps (pico seconds). Some CD have been known to measure in the several 1000s ps bracket, good player are generally sub 500 ps. Personally I would look to anything lower than 200ps for no significant audible problems and have my own player in the ‘comfortably sub 150 ps’ category! This is for audio. Video is similar and look for ¾ nanosecs.

    Some more general terms to help with the above

    Bandwidth
    The frequency range across which an audio system can reproduce sound. In most cases, bandwidth is given as plus or minus some level of decibels (usually 3 dB). In such a case, the bandwidth figure states that the system can reproduce a range of sounds at a useful level (plus or minus 3 dB) over that stated frequency. For example, the bandwidth of bookshelf speaker system may be given as 72 Hz to 22 kHz plus or minus 3 dB meaning that the system can reproduce a useful sound level all the way down to 72 Hz and up to 22 kHz. In such a system, there would be a lack of low frequency information making the use of a subwoofer desirable. Audio / video are just the same idea, only different frequencies.

    Cross talk
    An unwanted component in the signal due to deficiency of channel separation in the multi channels system. Crosstalk level may be given and measure in dB with reference to either an interfering or a wanted signal. E.g. Crosstalk is<-50dB at 5.5MHz.

    Chrominance
    The color portion of a video signal carrying the saturation and tint (hue) information for any given point in the image. Video signals are made up of color portions (Chrominance) and luminance (the information about brightness, darkness and contrast). Black, white and all the levels of gray have no Chrominance since they have no color - they need only the luminance portion of the video signal. The Chrominance aspect of a signal tells the video display what colors to use while the luminance portion of the signal gives the colors depth and contrast by adjusting the darkness and brightness of the image. Higher Chrominance levels produce more powerful or stronger colors (bright red versus pink). The abbreviation for Chrominance is "C."

    Luminance
    The black and white portion of a video signal which carries the information for brightness and darkness and contrast. Luminance ranges from pure black to pure white. When combined with the color portion (Chrominance), a complete video image can be developed. The Chrominance portion of the signal tells a video display what color to show. The luminance value adjusts the color to be light or dark, bright or shadowed so it has the proper contrast and color depth. Chrominance is abbreviated with the letter "C" and luminance is abbreviated with the letter "Y."

    Y/C
    Luminance (Y) and Chrominance (C); type of video signal transmission format that separates the color portion of the signal (Chrominance) from the brightness portion of the signal (luminance) resulting in higher picture quality compared to composite video, which combines the two into a single signal. A Y/C connection is often known as a S-Video connection. These cables carry the brightness and color information on two separate wires. When the two pieces of information are combined, as in a composite connection, they must be separated at the television by a comb filter or a notch filter. This separation results in some level of distortion. By separating the Chrominance (color) from the luminance (brightness), the distortions encountered by separating them can be eliminated.

    S-Video VCRs store video information as separate Chrominance and luminance signals so that they benefit particularly from using Y/C or S-Video connections. Laserdiscs store video information as a composite signal so Y/C connections may or may not benefit the picture quality. If the laserdisc player's filter for separating the Y/C information is better than the television's then using the Y/C connection is beneficial, but if the television's filter is better then using composite video is preferred allowing the superior TV filter to separate out the signals. DVDs store video information in yet another format.

    DVD video signals are split up into three components. The three signal components are the luminance (Y), luminance minus red (Y/R or Pr), and luminance minus blue (Y/B or Pb). These three components are labeled on the player as YUV, Y-Y/B-Y/R, or Y-Pb-Pr. The component video signals can create a picture free of distortions from dot crawl, color bleed, and other common distortions from combining and then separating the video signal components. A DVD player combines the luminance minus red and luminance minus blue signals into the Chrominance signal for Y/C video. This results in excellent quality, but the ultimate in picture quality from DVD can be had by using component video outputs (which use three separate coaxial interconnects with RCA/ BNC connectors instead of a Y/C's single connector with two individual conductors in one wire).

    Comb Filter
    Video display device that separates the Chrominance (color) and luminance (brightness) portions of a composite video signal. Comb filters are not required and not used with S-Video (Y/C video) or component video connections since those connections carry the Chrominance and luminance separately. A comb filter (or some other filter such as a notch filter) is necessary for any composite video format including laserdisc and television programming.

    A comb filter has a frequency response that resembles the teeth of a comb. It rejects and accepts small bands of frequencies on a regular interval moving up the frequency spectrum. One set of alternate frequencies carries the Chrominance (color) information while the other set of frequencies carries the luminance (brightness) information. The filter alternately blocks off sets of frequencies to accept color information only and then brightness information only effectively splitting up a composite signal into the two components (Chrominance and luminance). Comb filters are superior to notch filters in separating out the color and brightness information, however, they do add some distortions to the final image not present when a component or Y/C video format is used.

    less than 5000, I doubt it ;)
     
  10. lmccauley

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    :D
     
  11. karkus30

    karkus30
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    Just to throw some more coal on the fires, I once read there was good jitter and bad jitter not just quantities of. Sounds a bit like harmonics. Anyway the upshot for cd players at the time ( many people were fitting more accurate clocking circuits ) was that jitter in itself was not necessarily harmful. It only went on to prove that nothing is really quantifiable in the hi-fi world and sound quality is subjective, this probably applies even more to HC.
     
  12. Brad_Porter

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    Thanks everyone. Especially to Nic for his typical but much appreciated essay!!

    Cheers.
     

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