Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83 based; site hou2a.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!lll-crg!dual!qantel!ihnp4!houxm!hou2a!pjk From: pjk@hou2a.UUCP (P.KEMP) Newsgroups: net.video Subject: Re: Confusion in stereo Message-ID: <580@hou2a.UUCP> Date: Tue, 13-Aug-85 12:09:13 EDT Article-I.D.: hou2a.580 Posted: Tue Aug 13 12:09:13 1985 Date-Received: Sun, 18-Aug-85 21:05:28 EDT References: <3581@decwrl.UUCP> Organization: AT&T Bell Labs, Holmdel NJ Lines: 99 > From: lionel@eiffel.DEC (Steve Lionel) > > Jerry Askew's tale of the history of sound on videotape was, on the whole, > accurate, but omitted some key points and misrepresented a major > advance in the industry. Sorry Steve, but your article could use some clarifications also. I'm no expert in video myself, but I do read the various video rags. > signal. This new technique, named Beta Hi-Fi, was forwards and backwards > compatible with the original, mono linear Beta audio track. Beta Hi-Fi I not sure what you mean by "forwards and backwards", but if you mean that BETA (AFM) HI-FI is upward and downward compatible with mono BETA machines, I must state that while some current BETA VCRs can be upgraded to HI-FI by use of an optional adapter, this is not the case for pre HI-FI models. Therefore BETA HI-FI is not truly upwards compatible, except by expert modifications for older units (READ-> *expensive*). > using separate heads at different frequencies. What seems miraculous to > some, the VHS Hi-Fi VCR can pick up both signals with minimal interference > between them, and maintain compatibility with non-Hi-Fi VHS tapes. The first Please read up more on VHS AFM recording! VHS AFM uses "depth multiplexing" and head azimuth offsets to minimize interference with the video signal. Also, BETA HI-FI for PAL (and SECAM?) systems uses the VHS technique. > wow and flutter, a signal-to-noise ratio of about 75db or better, dynamic > range better than 80db and distortion about .3%. Note that since the > S/N ratio is so good (compare to a quality LP at 45%), there is no need > for noise reduction. However, to get the desired dynamic range, some > "companding" is done. S/N ratio and dynamic range are closely related items. The raw S/N of VHS AFM playback is something like only 40 dB, a noise reduction system called "HD" is used to increase the S/N to 75 dB - 80 dB. I believe it is a companding form of NR. BETA AFM NR is similar, I think, but the "raw" S/N is greater. [Someone correct ME on this if I am wrong!] > Hi-Fi machines played and recorded the linear track just fine. All was not > so well in VHS-land, however. While there was no reason why a deck couldn't > include both the stereo Hi-Fi circuitry and also have the Dolby-encoded > stereo linear tracks, some manufacturers opted to economize by only > having mono linear capability in their Hi-Fi machines. Thus, on these > machines, you can play VHS linear stereo tapes, but not in stereo and > without the Dolby processing. Other makers kept the stereo heads, but > didn't let you record in stereo on the linear track. Still others allowed > full functionality on the linear track. So, you have to be very careful > when shopping for a VHS Hi-Fi VCR if you care about linear track > compatibility. As far as I know, ALMOST ALL VHS HI-FI VCRs can playback the linear audio track in Dolby stereo. Many however, do not RECORD the linear tracks in (Dolby?) stereo. I myself cannot understand this, how much more expensive is it to include the extra circuitry to record in stereo? My VHS VCR, a QUASAR 5845, records the linear audio tracks in Dolby stereo. > > Well, that's our history lesson for today. Perhaps in a year or so, we'll > see if JVC manages to come up with something approximating SuperBeta. From > recent announcements, it doesn't seem that way. > > Steve Lionel > Sorry again Steve, but JVC just announced a picture enhancing technique for VHS. The new process raises the white-clip level from 160% t0 200% in pre-emphasis of the video signal and should make the picture appear sharper, especially at object edges. JVC has quietly included this enhancement in their HR-D140, HR-D250, and HR-D555 VCRs, and has made the technique available to other VHS manufacturers. JVC also working on another technique which could visibly reduce video noise. [This information had been recently posted to this group by someone else.] By the way: Does anyone know if the supposed compatibility problems between HI-FI VCRs [especially between Hitachi and Matsushita (sp?) models] have been eliminated? -- Paul Kemp ihnp4!hou2a!pjk