In a message dated 7/5/2006 13:00:41 Pacific Daylight Time, [EMAIL PROTECTED] writes:
Yes, it is hard. PAL is 4433618.75 +/- 5 Hz or +/- 1.12 ppm. NTSC is 3579545 +/- 10 Hz or +/- 2.79 ppm. That is straight out of ITU-R Rec. BT.470-6. The MPEG transport stream is clocked at 27000000 +/- 810 Hz or +/- 30 ppm. That is straight out of ITU-T Rec. H.222.0 :P You know, you are really demorilizing me now. Stop it! :P Hi Magnus, yup, that +-810Hz is the number I had in mind on the receiver side. The tighter <3ppm numbers you mentioned are for the broadcaster side I think. Although it sounds like a huge deviation from what we are used to discuss here (0.001ppb versus 30ppm) it presents a very challenging engineering problem since the factories don't want to pay more than about $0.25 for this 27MHz oscillator. Most TV's can achieve lock with larger errors (I've seen up to +-3KHz in some cases) and interestingly enough, the better the TV, the smalller the lock-range. Sony professional Studio Monitors cut back on the range to improve picture quality, and won't do much more than the 810Hz... Don't be demoralized, the fix is easy - feed a good 27MHz into your AV equipment (preferrably from a GPS Disciplined frequency reference. You could use our FireFox synthesizer for example - but that would be total overkill :) Also, to reduce the problem to a skipped-frame/repeated-frame issue you can use non NTSC/PAL baseband standards such as Component-out or HDMI out etc. bye, Said _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
