tutorials

There's been a little confusion around the industry about the differences between the DV based formats - namely DVCPRO and the other DV formats - Mini DV and DVCAM. We've put together a little Q&A to help make it all clear.

What's the difference between DVCPRO 25 at 4:1:1 & consumer DV and Sony's DVCAM's at 4:2:0 ?

4:2:0 means that line 1 is 4:2:2 but the next line is 4:0:0 (black and white, no colour sampling). In other words, each alternate line is luminance only, so for consumer use, or for transmission to the home with highly compressed MPEG2 signals, this is no problem - but certainly not for a serious acquisition format. DVCPRO 25 was designed to 4:1:1, because a broadcast recording must go through many dubs, via microwave or satellite links, or just normal multi-generational work in a studio. With every generation of 4:2:0, the vertical chrominance resolution is reduced, resulting in vertical chroma smear after a few generations of SDI or analogue dubs. DVCPRO 50 is 4:2:2 - with a lower compression rate of 3.3:1 - similar to Digital Betacam.

Can you do chroma keys on DVCPRO25 ?

Absolutely! Excellent keys are produced off DVCPRO 25 and DVCPRO 50 - but 4:2:0 sampling is the limiting factor for keys on DV / DVCAM.

What's the difference between ME & MP tape ?

ME Tape for DV&DVCAM for home use - MP Tape for DVCPRO for broadcast. The original DV group chose the ME tape for the very narrow track recording (10um) used in DV. But for DVCPRO, it was decided that although ME tape was the most suitable for the demands of consumers, it was not robust or mature enough for the broadcast and professional use - and that's why DVCPRO uses MP - Metal Particle tape. It is important to note that Digital Betacam SP and SX formats all use Metal Particle tape for robustness in the field and studio.

What DV format can play back all the other formats ?

Only DVCPRO has DV/DVCAM playback compatibility. All DVCPRO 25 VTR's , from the low cost AJ-D230 to the AJ-LT75 Laptop Editor, can playback DV and DVCAM tapes. It is always best however to use PANASONIC tape designed for DV use.

DVCPRO has a control track - DVCAM and Mini DV doesn't - Why ?

A control track is essential in any broadcast or professional analogue composite environment to help VTR colour framing. The fast servo lock of DVCPRO gives reduced pre roll times, and very importantly for broadcasters, instant start for live replay. For slow motion, a control track is a must.

How good is the audio on DVCPRO ?

DVCPRO 's better Digital Audio - the same as DAT - and features two channels of 48kHz/16bit. DVCPRO VTR's can also playback the 4 audio channels from DV tapes, but the 32kHz/12 bit audio in DV is seen as not of good enough quality for broadcast and professionals .

Who are some of the major broadcasters using DVCPRO ?

DVCPRO has become the defacto broadcast standard, replacing Betacam. It is the worlds most successful new digital format, outselling all other digital formats combined - some of the users are :

BBC News • Reuters TV • Granada TV • Scottish TV • Yorkshire TV • ITN • SFB • NRK • TV3 • TVG • TVE • Canal Plus • Shanghai TV • China Central TV • Nippon TV • Fuji TV • Tokyo Metro TV • GLOBAL TV • NBC • CBS • Benedek • Time Warner • WNET • WKJG • FOX • CBC • CanWest • Televisa • TV-Azteca • ZDF • ABC • Seven Network TV • Telecom Video • Mercury TV

The MiniDV tape format, although originally designed for domestic amateur use is now often used in the more demanding professional applications and broadcast. It generates surprisingly reasonable quality for its size, low capital cost and its low profile makes it a popular tool for low cost standard definition video production.

16x9 ON MINI DV

16x9 widescreen is now the requirement for Australian television since January 1, 2001, but all MiniDV cameras under A$20,000 can only produce a 4x3 image. While some can "switch to 16x9" in a fudged 16x9 mode - there is a considerable image compromise in the vertical resolution of your 16x9 image. In these cameras the 16x9 frame is created by losing the top and bottom of the camera's 4x3 CCD, normally 576 TV lines but now around 384 TV lines in its 16x9 mode. This "trick" 16x9 image cut out visually falls apart further when a 14x9 or 4x3 frame is extracted from it. This may be OK for home movies but not for professional use.

To solve the 16x9 resolution problem on Mini DV, Lemac offers an optical solution for small MiniDV cameras. (SEE RIGHT)

THE OPTICAL SOLUTION FOR MINI DV IN 16x9

An optical anamorphic lens attached to a Mini DV camera generates a 16x9 wide screen image, by optically anamorphisising or "squeezing" a wider image onto the cameras existing 4x3 CCD imager.

There are some disadvantages using this method:

1. The zoom range is limited to about half the range before the image loses focus.

2. Anamorphic attachments must be correctly positioned to create 16x9 in the correct geometry

3. The camera's 4x3 viewfinder only shows the image as a 16x9 squeezed image.

4. The geometry of these aspect ratio converters does not quite get to 16x9 but is close.

5. The anamorphic attachment needs to be kept very clean and well shaded to avoid flares.

The additional use of ND filters in bright conditions (which reduces depth of field) will reduce the visual effect of any dust on the anamorphic element.

WHAT TO BE CAREFUL OF WHEN USING MINI DV FOR PROFESSIONAL APPLICATIONS

REGULARLY CHECK YOUR MINI DV RECORDING

As the MINI-DV recording system was primarily designed for domestic amateur usage, it has none of the usual faulty recording warnings that broadcast equipment have. Therefore it is possible to unknowingly shoot unusable vision. To best avoid this potential problem, it is best to regularly check what you've recorded. The quickest way is to hit the "RETURN VIDEO" or "END SEARCH" button to inspect and review the last few seconds of the shot you last recorded.

As the error correction in MiniDV is quite powerful, its best that any test shot is not static, but moving. Moving, high detail shots (wide slow pans through trees on a windy day!) will better show up any defects in the video recording. If there are drop outs (digital blockiness in the image) or or even complete record failure, the most likely cause will be dirt on the record heads. It is wise to keep a MiniDV head cleaning tape handy to remove head clogs, but always be careful not to over use it - as they will wear the heads out prematurely.

THE MINI DV VIEWFINDER - CHECK ITS ACCURACY

Most MiniDV LCD viewfinders have a number of shortcomings and this can only be used as a framing guide.

These problems are:

1. FRAMING INACCURACY

Most MiniDV camera LCD viewfinders overscan the captured image, thus creating situations where you notice things, in shot that you'd never see through the viewfinder, appearing on your tape, such as microphones, light stands etc.!

Critical work on a MiniDV camera will require the use of an an accurate monitor for critical framing and so that you can understand the frame limitations of the camera.

A simple viewfinder framing test can be achieved by using Lemac's Frame + Focus Chart (supplied free with rental cameras, or as a sales item) to demonstrate the difference between what you framed through the viewfinder compared to the frame that you have actually recorded to tape. View the camera output on a good quality monitor in 'underscan' mode. The use of any lens adaptors, lens hoods, matteboxes and filter rings should be checked for vignetting on the monitor as this effect may not be visible through the camera viewfinder.

2. COLOUR & EXPOSURE INACCURACY

As the results from these LCD viewfinders can be quite different to what will be seen on television, once again its best to set it up by using an accurate monitor. See our section on monitors p 42.

If you are about to shoot in low light situations test for this, as often supplementary light is necessary for a useable result for both colour and exposure.

3. FOCUS INACCURACY

As the resolution of most MiniDV camera screens is quite low, using it for accurate focusing can be difficult, particularly under low light where the depth of field is low. If you're using the auto focus mode, bear in mind the system usually will focus on what is in the centre of frame and not the subject if it is offset to one side of frame. Using an accurate monitor to check focus during or prior to the shoot is advised.

Any lens adaptors should also be checked for resolution compared to using it without the adaptor. Cheap poor quality adaptors may be OK for your home movies, but not when you're trying to get the best out of the format. Also check what focus limitations the adaptor may create in the cameras zoom range.

MINI DV AUDIO

1. USING EXTERNAL MICROPHONES

Most mini DV cameras do not have balanced audio inputs and thus were not designed for external balanced equipment to be plugged into it. Various balance boxes are now available, and are recommended for serious use of MiniDV. These balance boxes are still limited by the connection hardware to the camera, which normally consists of a stereo mini-jack.

2. SET FOR 16 bit AUDIO

Make sure that the camera is switched via its menu to 16 bit audio and not 12 bit. 16 bit is the same bit depth as audio from a DAT recorder.

3. SYNC PROBLEMS

The audio on MiniDV is not 'locked' to the picture, so it is possible for it to drift out of sync.

There is no real solution for this other than to keep an eye on this during the edit.

MINI DV TIMECODE

Most MiniDV cameras do not generate a user controllable timecode, thus resulting in identification and edit problems for post production. Often the code resets itself to zero on power downs which creates a tape with multiple matching codes on the one tape - and that's an editors nightmare for an on line tape edit. If FireWire is being used say with Final Cut Pro on smaller edits, this may not be a massive inconvenience for you.

Good practice is when using MiniDV code - always "END SEARCH" after power downs to find the last generated timecode code with the last shot, so then when you next roll, not only will you have a clean edit, but also continuous timecode and happy editors! Also check under POST PRODUCTION NOTES.

MULTI-CAMERA & SOUND - DOUBLE SYSTEM FILM STYLE

By using AATON GMT timecode generating clocks to record timecode on the audio track of each camera and sound recorder, this will enable the use of multiple cameras, all locked together with jammed timecode from the AATON ORIGIN C MASTER CLOCK. This means that all cameras and recorders will have the same timecode, thus enabling normal multi-camera post production once the MiniDV tapes are transferred with this code to a broadcast format tape.

MINI DV TAPE STOCK

MiniDV uses Metal Evaporated tape (ME) - tape for home use - and while it is suitable for the demands of consumers, it is not robust or mature enough for the broadcast and professional use - and that's why broadcast tape formats use MP - Metal Particle tape. Panasonic tape is recommended as the most trouble free MiniDV tape that can be used in all MiniDV equipment because it completely complies with the manufacturers DV group specifications.

MINI DV POST PRODUCTION NOTES

On line edit note

If you are going on line for a tape to tape edit for broadcast, it is highly recommended that you digitally clone your MiniDV tapes to a low cost broadcast format such as DVCPRO25, generating fresh continuous timecode that does not repeat. This clone would then be used to feed your NLE suite and for any tape on-line if required.

If your production is to be shot over a long period of time - a digital broadcast tape clone of your rushes is highly recommended, because of the lack of MiniDV's archive capability.

Colour Correction - while a degree of colour correction is possible with MiniDV, its limitation for more control in post is its 4:2:0 sample rate. This also effects its ability in the negative for multi generational work and chroma keys.

Analogue / Digital Blanking - note that all MiniDV cameras generate analogue blanking.

Check out our paper on 'DV Formats - Not All Digital is the Same' (p.68-69) for more information.

MINI DV ARCHIVE NOTES

Mini-DV is NOT recommended for archive applications.

If the material is valuable for the long term, it should be digitally dubbed to DVCPRO25/50 or Digital Betacam, all Metal Particle tapes with solid recordings.