|
Good day Gentlemen,
Answers to some of your questions concerning SECAM. I live in Paris, France and receive it daily.
Analogue SECAM over the air transmissions will continue until 2012, our planned cut-off date. Transmissions are all in the UHF Bands IV & V, positive video modulation, AM mono sound + NICAM 728 digital stereo audio. NICAM is the same as pioneered by the BBC, but with a subcarrier adapted to the French L transmission standard (5.85 MHz, from memory).
In the meantime, all OTH programs are being duplicated with the DVB-T (Digital Video Broadcast-Terrestrial) system which is a pan-European standard. The transmitters are co-sited with their analogue counterparts and use the adjacent UHF channel run at -10 -15dB below the analogue power output. SD 625 video uses MPEG-2 encoding and terrestrial HD (1080i/50), due to start in early 2009 uses MPEG-4. Currently in Paris for instance, there are 18 Free-to-Air SD programs + another 8 which are encrypted and need a subscription & smart-card.
There was much debate over the MPEG-2/MPEG-4 issue. French broadcasters & set top box manufacturers urged the government to delay DVB-T until dual-standard IC decoder chips were available. As the opening of service was already 2 years behind schedule, the government said "No" and went ahead with SD/MPEG-2 service in April of 2005. Currently, about 70% of the population can receive DVB-T.
SECAM VHS recording:
Few people know this, but JVC adopted 2 entirely different schemes to record SECAM. The standard known as ME (Middle-East) SECAM records the color signal like a PAL VHS machine i.e. heterodyning the subcarrier frequency down to 629 KHz then correcting the unstable playback subcarrier upon playback with the machine's mechanical error speed variations to achieve a stable subcarrier. In the 1970s, this was the only way to achieve the high precision required of the chroma frequency without having a very expensive digital time base corrector.
ME-SECAM is used in the Middle-East, French overseas territories (Tahiti, island of the Reunion, Antilles, Guadeloupe, etc.). all these locations use OTH SECAM with negative video modulation and FM sound and are therefore very close to PAL B/G transmission standards.
For France, JVC decided to simply divide by 4 the 4.43 SECAM subcarriers (4.43 being approx the average between the 4.406 and 4.25 MHz SECAM subcarriers). Upon playback, the off tape 1.1 MHz chroma is simply multiplied back to 4.4 MHz. The beauty of SECAM on a VCR is that being FM modulation, it couldn't care less about mechanical instabilities. This is why AMPEX had great success selling industrial grade VTRs to French TV in the late 70s, because the machines had enough bandwith to record the chroma subcarrier directly and did not require a TBC to achieve color.
By then, the first 1" broadcast machines were appearing (AMPEX VPR-1 type A, then type C Ampex VPR-2, Sony BVH-1100,...) with 100K$ price tags! you could get 4-5 industrial machines for the same price...
The pictures shown by Eckard are not typical of off tape VHS SECAM. I have recorded over 800 tapes since 1977, and would never have put up with this type of defect on my movies!
I would say that this defect can show up with 1) excessive input luminance on the recorded signal, b) no 75 Ohm termination on the recorded or output video, 3)worn-out heads. Off course, playing color bars from a test tape on a waveform monitor would tell us more...
SECAM or PAL:
Very early on (late 60s) the French discovered that SECAM was a real PIA in production, especially in switchers (Vision Mixers for our UK readers). If you want to do a simple fade-to-black, you can't simply reduce the signal's amplitude as the FM chroma subcarriers remain at constant level, so for instance, the anchorman's (woman) face will get redder & redder as the Y signal diminishes and the chroma content increases relatively.
So, you must decode the SECAM into Y, R-Y & B-Y and attenuate all 3 signals at the same time, then re-encode into composite SECAM. In a nutshell, this means a lot of additional circuitry + unacceptable degradations from cumulative encode/decode processing.
So, very early on, PAL switchers were used, along with PAL cameras and VTRs and SECAM was only used for transmission by transcoding from PAL to SECAM the production chain's output.
PAL was adopted in production by private production houses & networks, however French state TV lingered on with SECAM for a while for political reasons, as this was still the "official" system adopted by France.
*FYI private TV networks did not appear in France until 1984. Before that, all Radio/TV on French soil was government controlled.
Many people in the French production industry were not satisfied with PAL. Although much more convenient than SECAM, it had its own set of quirks, for instance very difficult editing without horizontal "picture hops" at the edit point. Inquiry into this matter revealed the necessity for high stability Sync-to-H in the PAL subcarrier which in those days meant buying à 40K$ Tektronix Master SPG.
France therefore pioneered work in component analogue video in the late 80s, and coaxed suppliers such as GVG & Ampex to bring out component video products. This was a particularly enticing proposition as Betacam, then Betacam-SP were component recording formats, so a full component chain could be maintained from camera to master tape. Then component digital came along and the rest is history.
I hope i haven't bored you too much with this long post,
Best Regards
jhalphen
Paris/France
|