DVL-Digest 797 - Postings: Index - (2) DVCAM Walkman? - "Perry" Fred Greissing posted: >If DVCAM has a wider head, can you explain why a TRV-900, GVD-900, VX-9000, DSR-1000, all DV machines can playback DVCAM with no problems? Also how can a DVCAM machine read a DV tape without reading two tracks at a time?< In fact Fred, every Sony DV product except the original VX700/1000 camcorders play back DVCAM tapes but I've never seen this documented by Sony. They treat it as a 'Free Bonus' that you use at your own risk. The DVCAM heads are DEFINITELY wider than the DV versions, I've got a micrograph somewhere to prove it! Supposedly they are also built from longer lasting materials, and the bigger contact area would probably give longer life as well as giving a lower error rate. As to how it works; DV playing DVCAM is easy, you speed up the tape and the DV head plays down the middle of the wider track. DVCAM playing DV is more difficult and relies on a trick called azimuth recording; each of the two heads on the drum is tilted a few degrees in opposing directions, and this means that each head will not read high frequency components recorded by the other head. The digital signals recorded by DV formats are largely hf and therefore crosstalk between tracks, EVEN WHEN THEY OVERLAP, is minimal. Exactly the same scenario occurs with LP mode on consumer DV camcorders. The downside is that this crosstalk immunity was put in originally to allow tracks to butt with no 'guard bands', and to allow some inevitable mechanical tolerance. If you use up this tolerance with overlapping tracks then there is nothing left to cope with mechanical tolerances, and machines will struggle to play recordings made on another transport. It's a bit like us humans, we all have a built-in ability to cope with things that annoy us. If we wake up with a headache or get over stressed, then we use up this tolerance factor and can get pretty snappy! Perry Mitchell Video Consultant http://www.perrybits.co.uk (diese posts stammen von der DV-L Mailingliste - THX to Adam Wilt and Perry Mitchell :-) [up] |
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