Film-Tech Forum ARCHIVE: Newer Red LED's

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Posted by Alexander Alves (Member # 1746) on 06-25-2003, 12:15 AM:

Ive seen the older Cat701 Dolby Digital Reader giving a fantastically low error rate with brand new prints.After the life of the led is over, on changing the LED the error rate does is comparatively higher. Does this mean that the newer LED's are not good or they do not have the right wavelength? Who manufactures these LEDs? And why are they coming with reverse polarity?

Posted by Steve Guttag (Member # 268) on 06-25-2003, 08:31 AM:

The quality of the RED LEDs vary all over the place and always have. Some have great light output while some do not...some seem to last forever while others seems to die in a about a year or two.

As to the polarity. One of the cautions was that the polarity is not consistant. I have found that all of the RED LEDs to be identically polarized to each other. Likewise, I've found all of the IR LEDs to be polarized with each other. However, I've found that IR and visible RED LEDs have been opposite to each other.

Who supplies the bulk of the LEDs...why DOLBY, of course...why do you think they want the stupid things so much? It isn't because they are better, in fact they are much worse. If you want good performance from a digital reader, use white light, if you want good performance from a solar cell...use IR light, it is that simple. Dolby should have stopped with the Cat. 700 reader and the industry would have been much better for it.

Steve

Posted by Mark Gulbrandsen (Member # 72) on 06-25-2003, 09:02 AM:

Dolby has also overlooked the possibility of using a custom multiple array WHITE LED.......... I have to wonder if that wouldn't have been the best route to go for a solid state emitter.
The CAT 700 was by far the best of the lot of readers out there....
Mark

Posted by Manny Knowles (Member # 1171) on 06-25-2003, 04:56 PM:

Quick question -- How exactly do errors impact the presentation in the theatre?

For example:

Can we hear a difference between a "1" and, say, a "3"?

In terms of error rates, what is the threshold at which the system starts to sound bad or default to analog?

Posted by Carl Martin (Member # 1146) on 06-25-2003, 05:02 PM:

you shouldn't hear any difference until it fails. since it's digital, it works perfectly until it fails catastrophically.

carl

Posted by Manny Knowles (Member # 1171) on 06-25-2003, 06:04 PM:

That's what I thought but I figured I oughtta check before I go ahead and ask something like:

So what's the big deal? Why do we care if our error rate goes up?

And I don't mean that as a rhetorical...I'm really just asking.

Posted by Steve Guttag (Member # 268) on 06-25-2003, 06:11 PM:

Mark,

Dolby isn't interested in the white-light LED anymore than in the EPT lamp...neither makes them money. Come on, a $15.00US lamp that lasts over a year and is user changable...it is pretty tough to beat.

By using the visible red LEDs for everything, Dolby has been able to artifically inflate the red LEDs numbers that will, no doubt, improve their cost to Dolby and possibly allow them to give false quantities regarding the red-reader conversion (by merely stating a number on LEDs manufacturered rather than ever stating the quantity that actually went to analog readers).

Steve

Posted by Mark Gulbrandsen (Member # 72) on 06-25-2003, 06:44 PM:

Steve,
I wasn't thinking about Dolby's cost vs. profits, nor about EPT lamp life. I was thinking thata WHITE version of the LED array might be better noise wise. I'm quite sure it would cost a fortune to make them......figure about three times as expensive as the red is.
Mark

Posted by Manny Knowles (Member # 1171) on 06-25-2003, 11:33 PM:

So does anybody know the answer to my questions? I will re-state them...

(a) What is the highest error rate tolerated by SRD before defaulting to analog?

(b) At what point in the error rate number line should one become concerned about digital tracking errors?

Posted by Alexander Alves (Member # 1746) on 06-26-2003, 12:01 AM:

Manny,
Here in India it would be ideal to start with lowest possible error rates as films run here for maybe 10 to 15 weeks. So with print conditions getting worse with every run, we wouldnt like the processor switching to SR. Not that an error rate of 5 would sound any worse than say 3. Moral: The lower the error rate better the chances of the film running in Digital over its period of showing.

Posted by Adam Fraser (Member # 1074) on 06-26-2003, 12:10 AM:

Error rates of 7 or 8 are where we get concerned. Most new prints track 2 or 3 for us, used is usually around 5.

Posted by Steve Guttag (Member # 268) on 06-26-2003, 12:12 AM:

Manny,

The highest error number for Dolby Digital is "8". Sonically, the difference between 0 and 8 should be zero. The higher the number, the more the error correction has to work. However, if the error correction does work, the digital word is recreated exactly as it should so sonically there is no difference.

The error number is a decent indication of how well the system is reading the film. As the digital track becomes damaged, the more the error correction has to work. Also, as the reader system becomes less calibrated (focus, azimuth, light levels) so too will the error numbers increase. Generally, if you have a reader system that yields a steady 5 or better, then there isn't too much to worry about. However, if that same system that was yielding a 5 or better starts to consistantly rise over several weeks time to say 6. or 7...then there is an indication of impending failure.

More often than not, the cause is LED fade or the light source going bad. Also, generally as one approaches 8 on the error meter, the number of block failures (repeated blocks) also tends to increase and they are most certainly audible.

Steve

Posted by Mathew Molloy (Member # 666) on 06-26-2003, 01:07 AM:

Continual error rates of low 6's to 7 can be heard as what I refer to as 'blips' particularly during music/long tones. Of course the closer to F it gets the more those 'blips' can be heard in regular dialog.

Posted by Alexander Alves (Member # 1746) on 06-26-2003, 01:13 AM:

Hey guys you'll are all missing the point. What I wanted to know is are there multiple manufacturers of the LED's under discussion. Agreed to what Steve says some LED's die in a year and some last forever. Are there no standards? USL is also manufacturing LED's but none seem to match the quality of the Dolby LED's.

Posted by Mathew Molloy (Member # 666) on 06-26-2003, 02:36 AM:

Actually, Alexander, the thread wandered. Hope someone can answer your question though.

Posted by Michael Schaffer (Member # 1204) on 06-26-2003, 04:40 AM:

Manny: In the setup manuals for the digital processors, there is a section where the error rate display is explained and the actual number of errors which are reflected by the numbers on the display is listed.

Posted by Steve Guttag (Member # 268) on 06-26-2003, 07:15 AM:

To the best of my knowledge, Dolby single-sources the visible red LEDs. BACP/USL I believe have a similar LED as an alternative but I have yet to use it.

As to the "blips"...they are not a function of the higher error rate, persay. They are just uncorrectable errors. If you were to look at the Cat. 673 card's red LED...(with the cover off on a DA-20) you will see it flash anytime you hear a "blip" and that is a block failure. You will see the block failure flash even without the "F" coming on the 7-segment display.

However, you could run a solid 8 and never have a "blip." It is just that one usually begets the other. However, more frustrating is the low 0-3 errors that have blips. They are often caused by a well calibrated system that has motion stability issues. If the film weaves (either due to printing issues or soundhead issues) or has excessive vertical jitter, that is the chief cause of the low error number that blips (3,F, 3, F, 3, F....)

Steve

Posted by Jean-Michel Grin (Member # 1360) on 06-26-2003, 06:57 PM:

Hi Steeve,

Just a question about troubles with DA-20 digital decoder, linked with a CP-65:
The case happend sometimes; the digital track is played fine, but on the next trailer, who have an analog track only, the DA20 don't make the reversion to the CP 65 for the analog sound. And best, when the digital track is present on the next trailer, the DA20 work (all the channels Leds will blink) but no sound comes out of the speakers...

Have You ever seen that ?

Thanks for your answer an sorry for my weak English !

Posted by Dave Macaulay (Member # 813) on 06-26-2003, 08:20 PM:

To the best of my knowledge, Dolby is the only source for the red LED arrays used in SR-D readers. Other manufacturers use different heatsinks and mountings, and some trim the leads to fit their mounts if you order from them but the actual LED array still comes from Dolby... and Dolby is not telling where they get them from. Assuming you can mount the LED into the heatsink assembly (i.e. you have the necessary skill, and your heatsink isn't designed to make LED array replacement impossible), buying replacements direct from Dolby should cost less than buying from the reader manufacturer.
White LEDs? These are actually UV LEDs with a phosphor coating that gives off light that appears white. I've seen some hints that a mix of red green and blue pigments is used. I can't find a published spectrum so far, however I assume that it's probably rather spiky. I doubt if we should assume that the good performance of the Dolby incandescent white light penthouse would mean good performance from a white LED.
IR LEDs are a dead issue. The problem of not being able to visually see if the LED is working probably doomed them. The incompatibility with cyan tracks - regardless of whether you believe it's really coming, the industry has made a commitment to cyan - says "forget IR".

Posted by Gordon McLeod (Member # 33) on 06-26-2003, 08:46 PM:

To my knowledge all the LED used in reverse scan readers come from DOLBY as part of the patent licensing agreement

Posted by Steve Guttag (Member # 268) on 06-26-2003, 09:27 PM:

Oh I wouldn't consider IR a dead issue yet....I still have some venues where visible RED was removed for IR due to visible red not being compatible with legacy prints.

The industry really hasn't made a commitment to cyan...just bloated number and saber rattling. Now some countries may have made the commitment. Some countries definately have not.

Steve

Posted by Larry Zuverink (Member # 1483) on 06-27-2003, 08:49 AM:

From the sounds of it I'll be shot for saying this but we have far less problems with the 701 readers than the 700 readers. Maybe we got lucky with our 701's but I would install a 701 far before a 700. [thumbsup]

Posted by Steve Guttag (Member # 268) on 06-27-2003, 11:25 AM:

Your experiences are your experiences. They are not arguable nor should they warrant being shot.

As to the Cat. 700 vs the Cat. 701. I'm curious as to the problems with the Cat. 700. About the only one that will bite everyone is the dreaded power cable connector (overheats).

There is no physical way the Cat. 701 can out-track the Cat 700, presuming both calibrated to optimum.

If you like the Cat. 701, you'll love the Cat. 702 though...no pesky power supply and a "go/nogo" LED to indicate how well the reader is doing. One can adjust the LED (finally) without a scope while the show is going.

Another one to consider is the BACP reader which started the whole , no power supply and status LED thing.

Steve

Posted by Brad Miller (Member # 2) on 06-27-2003, 02:55 PM:

I've never seen the 701 outtrack the 699 or 700 either. That being said I've seen it come close, but always at least a point higher than one of the white light readers could run the print at.

While I'm thinking about it, I forget what the lifespan of the 699 and 700 bulbs are. I've seen these things run for 2 years without needing changing.

Posted by Alexander Alves (Member # 1746) on 06-28-2003, 02:56 AM:

The bottom line folks is that the LED's which we get here in India , if replaced in a Cat701 will never give the same error rate if it were a Dolby LED. So anyone who says that the LED's are manufatured by Dolby or any of their vendors is wrong. Maybe China has started making a few of their own too?? There is some major scam going on somewhere..

Posted by Mark Gulbrandsen (Member # 72) on 06-28-2003, 10:20 AM:

My experience has shown that the new BACP reader tracks as good or perhaps a tad bit better than the cat 699/701 penthouses does. But three is also special circuitry in there that looks at the light coming from the LED and makes compensation. The new Dolby CAT 702 also has this special USL developed circuitry weather they Dolby wanst to admit it ot not. Some trades were done between the two manufacturers as per the liscensing arrangements..... It does say Dolby Digital on the BACP!!Hummmm.....
Mark

Posted by Gordon McLeod (Member # 33) on 06-28-2003, 12:21 PM:

"give the same error rate if it were a Dolby LED. So anyone who says that the LED's are manufatured by Dolby or any of their vendors is wrong"
I think it is just sloppy alignment then as the led are made for dolby only

Posted by Dave Macaulay (Member # 813) on 06-28-2003, 12:33 PM:

It's possible someone has supplied a substitute LED array, Gilway has a few that look similar in their catalog and if I shopped around in Akihabara I could probably come up with something that would fit. I don't know how you could be sure that you have the "real" Dolby array - make sure you buy from a reputable dealer?

Posted by Steve Guttag (Member # 268) on 06-28-2003, 12:58 PM:

Dolby does not make them, themselves they are made to Dolby's specifications...I forget their vendor and I'm sure it is an exclusive agreement.

I have seen an alternative LED at one of the trade shows and I thought it was BACP that showed it to me. However, until something really is released, it is vaporware in my book.

Steve

Posted by Manny Knowles (Member # 1171) on 07-04-2003, 10:38 PM:

Wouldn't you just know it..?

Now I have a CP-500 (with Cat. 701) that's tracking 6-F and then totally reverting to Format 05.

Strange coincidence.