Someone has mailed me offlist to ask about something I should've
mentioned in my previous post.

Some video machines do seem to need syncs in order to record audio
properly. Most that I've tried over the years don't, luckily.

A friend of mine solved the problem by buying a cheapo video
test-pattern generator. About 15UKP (approx 25 USD) as I recall.  You
can get these from several mail order suppliers (check the ads in a
video hobbyist magazine) and possibly from Radio Shack or local
equivalent (e.g. Tandy in the UK).

Alternatively, with very little effort you could make a sync pulse
generator with a PIC to achieve the same effect.

I don't what system they use where you are but in the UK the TV system
uses  625 lines at 50Hz, interlaced. This corresponds to a  625*25 =
15.625kHz line frequency = 64uS horizontal sync pulse repetition rate.

I think the US uses 60 Hz * 525 lines but I could be wrong here. That
would be 15.750kHz = 63.492uS.


Sync pulses are normally 0.3V negative going and any video (picture)
signal goes up to 1V peak which represents white.  0V = black.  You
won't need any picture to sync the recorder for audio.


Here's a (poor) illustration of what it'd look like.




-------------------------------------------   1V. Typical peak level
                                              of picture information.





______  ______  ______  ______  ______  0v
      ||      ||      ||      ||
      ||      ||      ||      ||
      --      --      --      --        -300mV





I also found this in an old file:


"DigiKey lists 74ACT715PC-ND as "Video Synchronous Generator NEW!" It is
a 20 pin DIP and costs $17.50 each for small quantities. The
surface-mount version is SC instead of the PC in the above number. You
have to pay an extra $1 for the datasheet if you want one."



I'm lucky, my Panasonic recorder works quite happily with no video syncs
connected.



Cheers.


Andy.











    .-.
   /   \           .-.                                 .-.
  /     \         /   \       .-.     _     .-.       /   \
-/-------\-------/-----\-----/---\---/-\---/---\-----/-----\-------/
          \     /       \   /     `-'   `-'     \   /       \     /
           \   /         `-'                     `-'         \   /
            `-'                                               `-'



------------------------------------------------------------------------