Proper Monitoring

Just like good lighting and camerawork are some of the fundamentals of quality production, good monitoring provides some of the same important building blocks for post-production. Without high quality video and audio monitors, as well as waveform monitors and vectorscopes, it is impossible to correctly assess the quality of the video and audio signals with which you are working. There are few if any instruments that truly tell an editor or mixer the degradation of signals as they travel through the system any better than the human eyes, ears and brain. You cannot read out the amount of compression applied to a digital file from some fancy device, but the eye can quickly detect compression artifacts in the image.

 

Such subjective quality evaluations are only valid when you are using professional, calibrated monitoring that shows you the good with the bad. The point of broadcast grade video monitors and studio grade audio monitors is not to show you a pleasing picture or great sounding mix, but rather to show you what’s actually there, so that you can adjust it and make it better. You want the truth and you won’t get that from a consumer video monitor or TV or from a set of discount boombox speakers.

 

Video Monitors

 

Let’s start with the picture. A proper post-production suite should have a 19 or 20-inch broadcast grade monitor for video evaluation. Smaller monitors can be used if budgets are tight, but larger is better. Most people tend to use Sonys, but there are also good choices from Panasonic and Barco. In the Sony line, you can choose between the BVM (broadcast) and the PVM (professional, i.e. “prosumer”) series. The BVMs are expensive but offer truer colors because of the phosphors used in the picture tube, but most people who work with properly calibrated PVM monitors are quite happy with the results. In no case at this point in time would I recommend flat panel monitors as your definitive QC video monitor – especially if you do any color-correction with your editing.

 

The monitor you use should have both component analog (or SDI) and composite analog feeds from your edit system. Component gives you a better image, but most of your viewers are still looking at the end product (regardless of source) via a composite input to a TV or monitor of some type. Frequently things can look great in component and awful in composite, so you should be able to check each type of signal. If you are using a component video feed, make sure your connections are solid and the cable lengths are equal, because reduced signal strength or unequal timing on any of the three cables can result in incorrect colorimetry when the video is displayed. This may be subtle enough to go unnoticed until it is too late.

 

Properly calibrated monitors should show a true black-and-white image, meaning that any mage, which is totally B&W, should not appear to be tinted with a cast of red, blue or green. Color bars should appear correct. I won’t go into it here, but there are plenty of resources which describe how to properly set up your monitor using reference color bars. Once the monitor is correctly calibrated, do not change it to make a bad picture look better! Fix the bad image!

 

Scopes

 

Video monitors provide the visual feedback an editor needs, but waveform monitors and vectorscopes provide the technical feedback. These are the editor’s equivalent to the cinematographer’s light meter. The waveform monitor displays information about luminance (brightness, contrast and gamma) while the vectorscope displays information about color saturation and hue. The waveform can also tell you about saturation but not hue. Most nonlinear editing applications include software-based scopes, but these are pretty inadequate when compared to the genuine article. Look for products from Tektronix, Leader, Videotek or Magni. Their products include both traditional (CRT-based) self-contained units, as well as rack-mounted modules that send a display to a separate video monitor or computer screen. Both types are accurate. Like your video display, scopes can be purchased that take SDI, component analog or composite analog signals. SDI scopes are the most expensive and composite the least. Although I would recommend SDI scopes as the first choice, the truth of the matter is that monitoring your composite output using a composite waveform monitor or vectorscope is more than adequate to determine proper levels for luma and chroma.

 

Audio Monitors

 

Mixers, power amps and speakers make up this chain. It’s possible to set up a fine NLE suite with no mixer at all, but most people find that a small mixer provides a handy signal router for the various audio devices in a room. When I work in an AES/EBU-capable system (digital audio), I will use that path to go between the decks and the edit system. Then I only use the mixer for monitoring. On the other hand, in an analog environment, the mixer becomes part of the signal chain. There are a lot of good choices out there, but most frequently you’ll find Mackie, Behringer or Alesis mixers. Some all-digital rooms use the Yamaha digital mixers, but that generally seems to be overkill.

 

The choice of speakers has the most impact on your perception of the mix. You can get either powered speakers (no separate amp required) or purchase a separate power amp, depending on which speakers you purchase. Power amps seem to have less of an affect, but good buys are Yamaha, Crown, Alesis, Carvin and Haffler. The point is to match the amp with the speakers so that you provide plenty of power at low volumes in order to efficiently drive the speaker cones.

 

Picking the right speaker is a very subjective choice. Remember that you want something that tells you the ugly truth. Clarity and proper stereo imaging is important. Most edit suites are near-field monitoring environments, so huge speakers are pointless. You will generally want a set of two-way speakers, each with an eight-inch woofer and a tweeter. There are plenty of good choices from JBL, Alesis, Mackie, Behringer, Tannoy and Eastern Acoustic Works, but my current favorite is from SLS Loudspeakers (Superior Line Source). In the interest of full disclosure, I own stock in SLS and have them at home, but they are truly impressive speakers sporting innovative planar ribbon technology in their tweeter assembly.

 

VU Metering

 

VU, peak and PPM meters are the audio equivalent to waveform monitors. What these meters tell you is often hard to interpret because of the industry changes from analog to digital processing. An analog VU scale places desirable audio at around 0 VU with peaks hitting at no more than +3 db. Digital scales have a different range. 0 is the absolute top of the range and 0 or higher results in harsh digital distortion. The equivalent spot on this range to analog’s 0 VU is minus 12, 14 or 20 db. In effect, you can have up to 20 db of headroom before distortion, as compared to analog’s 3 to 6 db of headroom. The reason for the ambiguity in the nominal reference value is because many digital systems calibrate their VU scales differently. Most current applications set the 0 VU reference at –20 db digital. 

 

Mixing with software VUs can be quite frustrating because the meters are instantly responsive to peaks. You see more peaks than a mechanical, analog VU meter would ever show you. As a result, it is quite easy to end up with a mix that is really too low when you go to a tape machine. I generally fix this by setting the VTR inputs to a point where the level is in the right place for the VTR. Then I may change the level of the reference tone at the head of my sequence to match the proper level as read at the VTR. This may seem backwards, but it’s a real world workaround that works quite well.

 

© 2004 Oliver Peters