
rob aylestone
Moderator
The aim of all helical scan recorders was pretty much the same - to be able to record on a slow moving tape a signal with a frequency response as high as possible. Rich's explanation was a good one, simplifying a quite complex process. Instead of being an air traffic controller in the RAF (my intention after education) I somehow got a job selling the new fangled video recording gear. Sony U-Matic to businesses - like Shell, doing the installations and then training! Yes, we had to teach people how to put tapes in and press record! We had Philips domestic recorders being put into schools to record the schools programmes, and a tiny number of very rich domestic customers. To put it into perspective, a 1 hour cassette cost £20. I earned £22 a week, and the Philips recorders cost £620! The Sony's were over a grand for the playback only machine, the record button version more expensive. Frequency response set definition. The commercial machines could on some, replay NTSC 525 line tapes as well as our PAL 625 line system, but the recording system struggled to get much over 200 lines of resolution when measured. Reduced top end reduced the sharpness of the picture, and unlike audio, the noise in the signal didn't really impact that much. Newer versions of the commercial and domestic machines, gradually crept the resolution up as the specs morphed into new ones. The audio, however was terrible until the stereo FM system was introduced. Most end users had no idea at all. So many never even pressed the button and listened in low-fi mono for ever. Colour was sort of superimposed on the brightness info - this is what appeared to be the 'sharpness', and colour was plonked on top - controlled by a little burst in the waveform. If the entire waveform was a Volt, peak to peak, the little colour burst and sync pulse at the start of each frame/field was about 1/3 the level - enough to be recognised. When people copied the tapes, the resolution dropped, but these pulses also got mangled and you would lose the colour, or the lock, or both. Macrovision mangled it deliberately, just enough a recorder could still lock to, but copying the tape magnified the mangling. The secret was to run through a device that was designed to replace dodgy sync pulses and replace them with brand new nice ones - the early effects and vision mixers did this as part of the design, and defeated macrovision very well - inserting new syncs - just was the illegal copying industry needed. The commercial broadcast style VTRs often had more audio tracks - but audio was just sort of just good enough. The hifi machines were grabbed by audio folk because they just 'accidentally' did audio really well. Annoyingly many when they first came out had to have a valid video signal present. No video, no audio. Later ones detected the lack of video and recorded internally generated black.