Mb/s issue -- Firestore or Tape?
 

I'm using a Canon H1 on an upcoming feature, and I don't know if I want Firestores or not because I have a question. Nobody seems to be talking about the quality of the compressed firestore image versus the compressed tape image.

I talked with the Birns and Sawyer folk here in LA, who along with a bunch of DPs, screened footage from the new Canon and Panasonic on a giant movie screen and were impressed with the Panasonic (they didn't have a chance to see that much) but were completely "blown away" by the Canon (with a straight face they said it looked 90 - 95 percent as good as the F900!)

According to those there, the HD-SDI output (1.4 G/s) and the HDV tape (25 mp/s) output were both amazing, with some loss on the tape but not anything like what they had guessed. It looked fantastic. Confused, they asked and were told that the HDV tape actually gets up to 40 Mb/s, not 25, which helped explain it. (They were still amazed).

So to my point, if the tape gets more like 40 mb/s, will I be losing image quaility if I use a firestore? I looked at some specs that said the firestore was 25 mb/s. Is that right? Does it actually get more?

If there's a difference (ie. the tape is better), I'd rather spend the time capturing it all than lose that much image quality (this may be a film-out).

I realize this is all on the vanguard, and I'll be attending a seminar and B and S at the end of the month where I'll try to get them to screen this stuff (if anyone from there is reading, do it), but if anyone has any thoughts , please rock on with them.

Your confusing a whole slew of things here.

HD-SDI is approx 1.5gigabits / second - its fully uncompressed

HDV records to tape with a data rate of 25megabits/second - no more and no less - full stop. (The tape records crc data at about 8 mb/s and their is another few megabits for audio, but not much.)

Firestore does not connect to HD-SDI. It connects to the firewire port and captures exactly what is written to tape. Therefore the reason their is not quality comparison is because they are digitally identical.

So both tape and firestore not only record the exact same data rate but the exact same information too, so their is no comparison to be made.

You should also take into account that unlike tape, there is practically no chance for dropouts, caused by things like dust or minute defects in the tape surface, when recording to a HDD like with a Firestore or one of the other D2D solutions. This will also have a positive effect on the quality of the image recorded, due to the absence of pixel errors. (At least this applies to DV, I don't know if the issue of dropouts is the same with HDV)

[QUOTE=Keith Wakeham]Your confusing a whole slew of things here.

HDV records to tape with a data rate of 25megabits/second - no more and no less - full stop. (The tape records crc data at about 8 mb/s and their is another few megabits for audio, but not much.)

QUOTE]

thanks. i wonder why someone would say it records more like 40 mb/s than 25 if that's not possible? because of some compression trickery? these are pros talking this way, so there is probably SOME basis for it.

regardless, i think what you're saying is, whatever goes to tape goes to the firestore, be it 25 or the 40-ish they claim.

Ya, same to tape as to firestore.

Now, if you want to check out the exact datarates for the tape transport mechanism are listed at wikipeda.org

http://en.wikipedia.org/wiki/Dv

And some quick infor on HDV is at http://en.wikipedia.org/wiki/HDV

I don't quite see where anyone can get 40 megabits/sec - doesn't rightly make sense at all to me and I crunch a lot of numbers dealing with video daily. XDCAM HD I think does 35 mbit/sec mpeg-2 in HD, but not 40. Maybe they meant 4.0 Megabytes a second, which is close to the actual 3.6 mbytes that are recorded to disk

i think the B&S guy said "gee, that looks good for 25 mb/s." And the Canon guy replied "Well, it's really more like 40." And it went downhill to me from there.

So the firestore is about a whole lot of convenience, saving the heads if you're capturing via camera, and gives you a back-up/archival tape, got it.

Great board. Thanks again.