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| Difference between phase response and group delay |
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| IconicPCB:
VK6, I appreciate Your comment and have no problems with it however it under normal circumstance. It is not applicable in case of a cable TV set up ( CATV/MATV ) since excessive group delay through the cable does in fact result in delay between Chrominance signal and luminance signal resulting in a colour dsiplacement on screen. I also appreciate the NTSC/PAL/SECAM advantages and shortcomings. PAL will correct colour but will not correct for group delay through the transmission line. The only practical solution is an all pass network with minimal insertion loss correcting for group delay inequality in the cable at the particular band. The human eye is good for about 0.5% distortion ( -47dB ) before it finds image objectionable Unfortunately due to old age and lack of use ( last accessed during early eighties) , I can not recall the exact specification on group delay ( nano seconds ) inequality across the channel width before the eye complains. I shall try to dig this information up for sake of completeness of argument. |
| aandrew:
Orolo, how are you generating those images? Nice mathml too, tell us your secret! |
| IconicPCB:
A quick search points to group delay inequality within a channel of 75nS ( another source suggests 170 although i think 75 is probably more appropriate). This group delay inequality will result in on screen displacement between chrominance and luminance content. I think it is fairly straight forward to calculate the number of lines of horisontal scan per second and calculate the DURATION of one horisontal line. The line duration places the 75nano seconds in perspective in terms of percentage displacement of chrominance and luminance in the line and therefore a feel for objectionable distortion on screen. I hope this clarifies the example quoted. |
| orolo:
--- Quote from: aandrew on October 13, 2017, 12:07:24 am ---Orolo, how are you generating those images? --- End quote --- With a wonderful package from your country, Maple. There are some extremely talented mathematicians developing it; we used Mathematica at college but, after discovering Maple, I switched and never looked back. Regrettably, my version is a bit old and win10 seems to dislike it. --- Quote ---Nice mathml too, tell us your secret! --- End quote --- It's \$\LaTeX\$! I can't thank enough the guys who developed the LaTeX add-on for blogs and forums, it's easy to use and a game changer. But I understand that abusing it can come off as pedantic or annoy people who don't like math that much. |
| fonograph:
I want to say (type) big THANK YOU to Orolo for extensive effort to explain it to me,such thing is rare occurence and I want to express my gratitude. I still dont understand :-[ If you still have patience,I have idea how you can explain it to me.I will need two 2D pictures,horizontal axis is time,vertical frequency,like a spectrogram,and show three sinewaves with start and end points before and after going frequency specific group delay filter and phase shifting filter for comparsion for example,each sinewave cycle is split into 4 parts,each part represents 1 quarter of cycle,250 milisecond delay of 1hz sinewave would look like one character shift. 100hz 123412341234123412341234123412341234 50hz 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 25hz 1 2 3 4 1 2 3 4 1 2 3 4 1 2 a 180 degree phase shift at 50hz would look like this 100hz 123412341234123412341234123412341234 50hz 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 25hz 1 2 3 4 1 2 3 4 1 2 3 4 1 2 or is that how 50milisecond group delay at 50hz would look like? I am not sure.If you could manage to show me this way how the relative position and phase changes that I think would finaly allow me to understand it. |
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