JVC DVDR/HDD DualPass recording system test... join in the fun!

[StuR]

I've been meaning to post something on this since getting a JVC MH300 as I'd like to see how it compares to other HDD recorders. The JVC DualPass system is on pretty much all the HDD/DVDR combi's I've seen. It means that as you rec to HDD the amount of detail/action per frame is monitored so that when you dub to DVDR this info can be used to increase or decrease to bitrate more efficently.

That's the theory so to test I've used a 2min rec and 'MPEG-2 Validator' to show the bitrate graph for differing rec settings.

Test 1.
- 2min clip from an unprotected DVD, title sequence
- first rec direct to dvd at SP (120min)
- second rec at XP (60min) to HDD and dub to disc at SP
- third rec at DV quality and dub to SP


Results

Comparing the graphs I'd say firstly rec. in DV is not worth it, XP is fine unless your using DV tape source.

On the graphs the main points are
A - about 10sec of menu (so a still which should be lowest bitrate)
B - a peak caused by a shot from a car window of trees going by.
C - a peak caused by a shot looking into a car windscreen which has tree reflections in it.

Comparing direct recording to dualpass-
the dualpass XP>SP lowers A from a trough of 3.5>2.9
increases the peaks at B from 6.1>6.6 and C 6.8>7.9
and lowers the average bitrate from 4.4 to 4.25
This appears to be producing a better DVDR at SP.

NOTE- visually its hard to tell a difference but if you push the FreeRate beyond 120min it should be even more useful.


I'd be really interested to see if someone with a Pioneer and Toshiba HDD/DVDR could repeat this test to see if they improve the bitrate when re-encoding to dub a DVDR. They may well be as effective without even referring to it as a feature.
Any DVD source is fine as long as you have a still image section for a while and some good peaks to compare easily.

[StuR]

Whooow there, don't all rush in
I'll even except comparisons to Sony and Panasonic HDD/DVDR's
not to mention any others.
go on it won't take long