|  IP: Logged

 |  IP: Logged

A 1dB error might not seem like much but it can be enough to cause slight audible mistracking, particularly with A-type, which is less tolerant of errors than SR.

(Note that with Panastereo processors the LED meter is independent of the NR subtraction so any format can be selected when setting Dolby tone. A more sensible approach wouldn't you agree?)

------------------
Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935

Whilst we have certainly come up with a method of verifying the lateral position of the soundtrack (we bought an expensive measurement microscope and compare our test films to the relevant SMPTE standards), we have not yet determined a reliable and highly accurate way to verify such things as level and frequency response characteristics. But we are exploring several ways of doing this.

In the meantime I would suggest the following:

For Cat69T Dolby tone if you have several batches of NEW (unworn) stock which disagree with each other, choose the batch with the lowest output level and use it as your reference. It is better to err on the side of setting your preamp gain too high than too low for several reasons. Too low a setting may cause pumping of low level dialogue particularly with Dolby A films, whereas setting the gain too high will make things sound a bit brighter, the latter being less objectionable than the former. Secondly, film prints themselves will vary in calibration from one to the next so once again, erring on the high gain side will give less objectionable errors.

For cat69P we have found that the most recent (pale pink coloured) stock has the flattest response. The dark pink stuff has a severe roll off in the 16kHz - 20kHz region and the old B&W stock is not a whole lot better (at least not using red LED readers).

For cat97 (left/right) the important thing is lateral alignment and you can compare your stock by carefully overlaying it with some BT-35. Cat 97 has two alternate burst sine wave signals printed as a negative soundtrack running down the centre of each track, wheras BT-35 has two square wave signals runing down the outer edges of the soundtrack area. Using a magnifier you can check that the outer edges of the Cat97 waveforms are both exacty the same distance from the inner edges of the BT-35 square waves. Be careful to accurately align the edges of the two films on the soundtrack side.

That is the best I can offer at this stage, but we are working on it. Maybe someone from Dolby can offer something more conclusive as they make the stuff!

The indecison is driving me to drink!

Where's the Gin

 |  IP: Logged

 |  IP: Logged

 |  IP: Logged

Playing analog A prints also has a horrendous amount of distortion in the audio when the actual Dolby loops are used. The level meters will pin themselves during program material. I am hoping that I just got a bad batch, but even if that is the case that really blows.

Our pal Steve Guttag has devised some way of verifying Dolby tone, but he hasn't shared it yet. Steve?

 |  IP: Logged

It is possible to measure the peak to peak excursion of the Dolby tone sine wave with a microscope to verify that it occupies the correct track width for a 50% modulated signal, but this is complicated by the fact that the level of the tone could vary quite significantly along a short section of film and yet still average out to give a correct reading on a meter.

If the Ultra 50% tone is considered to be more accurate, maybe Clint can let us know how they verify that their stock is "on the money".

Of course, any consistant difference between Dolby's and Ultra's 50% levels may come down to one company's definition of 100% modulation vs the other's. The maximum track width "available" per track for SVA prints is set down in the SMPTE standards. However I seem to recall that the standards are not specific on whether you should consider 100% modulation to be the entire available track width, or something a little less to allow say, for sideways weave. I also seem to recall that Dolby uses something less (like maybe 90%), but I do not recall exactly what that something is. Where is Steve Guttag when you need him? This is one of the problems when individual companies are permitted to set their own standards.

------------------
Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935

 |  IP: Logged