By: Hal Robertson
Email [email protected]
During the course of setting up a video shoot, sound is usually one of the last things considered. This is unfortunate because regardless how much you spend on the set or the talent, audio has the power to make or break your video. I can’t tell you how many :professional” product videos I’ve seen that sound like they were recorded with a consumer camcorder. The point is, even though the packaging is dazzling and the video is gorgeous, if the audio stinks, it cheapens the value of the entire project.
In this section, we will deal with audio-for-video as it applies to different tape formats and how to get that audio on your tape
• Audio For Video Part 2
• Audio For Video Part 3
VHS and S-VHS use the same methods for sound recording and reproduction, so we’ll start with them. There are two separate types of audio on a VHS tape – HiFi and Linear. The HiFi track is stereo, has a broad dynamic range and very low noise. In fact, when properly recorded, you would have a hard time distinguishing it from CD sound. HiFi audio is recorded (with a separate head) along with the video signal as the tape passes by the rotating video drum. Linear audio is recorded along the edge of the tape with a stationary head – just like a cassette deck.
8mm and Hi8 use a method similar to the VHS HiFi approach, except Sony has dubbed this “AFM”; audio (Audio Frequency Modulation). AFM is usually mono on 8mm cameras and stereo on Hi8 decks. Although the specs are not quite as good as VHS HiFi, the sound is very clean. There is no provision for linear track audio on the 8mm format. Some Hi8 decks (but not all) include a stereo digital soundtrack recorded separately from the AFM sound. The quality of this digital soundtrack is similar to FM radio and has the added ability to be recorded after the video has been shot.
Although most people don’t shoot on 3/4" tape today, you may edit to it from time to time, so we’ll go over that too. 3/4" tape – or U-Matic – uses two independent linear audio tracks, recorded along the edge of the tape similar to VHS. The difference here is that each track can be recorded independent of the other, at any time in the production process. There are several ways to take advantage of this capability. The most obvious is you can record a stereo soundtrack if you are shooting a music program. Most news crews use one channel for location background noise and the other channel for the on-camera talent. This allows a lot of flexibility later while editing. You can also use one channel for your narrator/on-screen talent and the other for a music bed.
The new DV formats have a couple of options (although not available on every camera). You can choose a high-quality two-channel mode that records CD quality digital stereo sound. You can also choose a slightly lower quality four-channel mode that records two independent stereo pairs of digital tracks – one pair for the shoot and another pair for voice-overs or post-production tricks. One more interesting DV audio goodie: Many DV cameras allow a "Still" or "Photo" mode where the video camera becomes high capacity still camera. While shooting the still shot, you are allowed a few seconds to record verbal notes. The audio quality is mediocre but handy for sorting things out later.
ADVANTAGES AND DISADVANTAGES:
Each tape format has it’s own little audio quirks and idiosyncrasies, but none so much as the VHS/S-VHS camp. Since the HiFi soundtrack and the linear audio track are located in different physical locations on the tape, most industrial and professional decks (and some camcorders) allow for audio and/or video insert editing. This means you can replace various segments of your master tape at will as you edit – this is very handy. Unfortunately, it also imposes certain limitations and causes some problems.
As we mentioned, the linear track is recorded separately from the HiFi track so you can replace some or all of the linear track audio on your edited master. This is all well and good, but you must settle for sound quality on par with cassette tape (with no noise reduction). So why can’t you use the HiFi track instead? Well, you can if your program consists only of direct cuts from your source tapes – with no additional narration or music. Those of us producing training, marketing and special interest videos can’t usually do that. Since the HiFi track is recorded (combined, really) with the video signal, whenever you edit the video portion of your master, you are editing the HiFi audio track as well. This can make for some pretty choppy audio. It also makes silence when you insert a still shot or title in your video.
OK, the linear track sounds bad and the HiFi track is impossible to manage – so now what do you do? Here is a trick I learned over the course of 3 years producing training and marketing videos exclusively on S-VHS equipment. It’s not perfect, but it works. Let’s use a marketing video as an example. All good marketing videos contain testimonials and/or the CEO on camera, right? But you also need to manage a narrator (or two) and some fill music. First, assemble your video as per the script (or storyboard) – titles and all. The only difference is to record silence during the clips that will ultimately have the narrator or music over them (just unplug the audio cables or turn down the audio at your mixer. Don’t just turn down the record volume on the record deck – it usually doesn’t affect the linear track). All testimonials are recorded with sound, fading in at the beginning and fading out at the end. Next, time the entire video, top to bottom – making notes about specific audio cues (narration for a clip, graphic or sound effects). The next step is to produce the soundtrack, complete with music and timed narration – leaving silent gaps for the testimonials. Then, starting at the beginning, audio dub (or insert) the soundtrack on the linear audio track of your master, making sure to dub silence during the testimonials. It may take a few tries to get the timing right, just be patient.
Now, the playback. Virtually all S-VHS decks (and a few camcorders) have a switch or button that allows you to choose to listen to the HiFi audio, inear track audio or a mix of the two. You need to find the "mix" option. When you play the finished video, you will magically hear the soundtrack, narration and testimonials in perfect alignment (or as close as your gear allows). You may need to fudge on the narration start and end times, allowing some extra slop at each end. You will probably find the HiFi track plays louder than the linear track. Just record the testimonials at a slightly lower volume. Experiment till you find the right blend.
This will work in many situations with a few tweaks but here are some important tips. You MUST record silence or the soundtrack on the linear track throughout the ENTIRE video. If you don’t, you will likely hear a strange echo or reverb during the testimonials. This is because the HiFi and linear tracks are seldom in perfect alignment – you are hearing both at slightly different times. Remember, you cannot play the master tape in a deck that does not have an audio mix switch. Along the same lines, if you are sending the master out for duplication, make sure your duplicator knows about your audio trickery and can compensate. You might also make a note on the label or box indicating the "multi-track" audio so you don’t forget to flip the switch six months from now.
This trick (or a modified version) will work on some of the other formats as well. Specifically, Hi8 and DV with the additional digital soundtrack, and 3/4" tape with it’s two independent audio tracks. If you have the privilege of editing your videos in a computer, you probably don’t understand why this is such a big deal.
Now that you know how the different formats record and play back audio, how do
you get the sound onto the video in the first place? Unfortunately, there is a different answer for just about every camera on the planet so I’ll try to simplify things.
If you are shooting with a consumer or pro-sumer camcorder, your only input option is probably the 1/8" mini microphone jack (if your camcorder even has one!). On some cameras this is a mono (single channel) mic jack – on other cameras it is stereo (dual channel). The hardest part is just getting plugged in. These mic jacks are typically near the built-in mic, opposite the viewfinder – not the most convenient location. A trip to your local Radio Shack can remedy this if you are willing to spend $20-$25 and use a string of adapters almost 8" long! Several companies have addressed this shortcoming lately with adapters designed for professional "XLR" microphones and other audio devices. This seems like a much better solution. You can also build an adapter for a single professional mic if you are handy with a soldering iron and have some patience (more on this later). Just remember that whatever you plug into this microphone jack, the cable should not be any longer than 20-25 feet. Otherwise, you will experience noisy sound and possibly interference from a local radio station (or two). You should also know that you cannot attach a cassette deck or CD player to this input – your sound will be distorted and garbled at best. These devices output "line level" signals that are many times louder than that of a microphone.
There are a few industrial-grade camcorders that include microphone and line level inputs (the Panasonic AG-460 and Sony V1000 leap to mind) along with input level meters. This makes hookup a breeze and is very convenient for one-man operations because all the connections and adjustments are centralized. Unfortunately, most manufacturers aren’t this forward thinking or are too miniaturization-minded. At the other end of the scale are some of the new DV cameras that require special adapters (not included!) to attach an external microphone. Sony is famous for this in their audio products and continues the tradition in some DV products.
Some industrial-grade and virtually all professional-grade equipment allows you to plug a professional microphone directly into the camera. Professional microphones have an industry-standard 3-pin "XLR" type plug that snaps in place. This is called a "balanced" connection and allows cable runs of several hundred feet without any significant loss or interference.
If you are shooting for a living or serious hobby, bite the bullet and buy a real microphone mixer. No, not one of those toys they sell in the backs of the video magazines – you need a real honest-to-goodness professional microphone mixer. They are not as expensive as you might think and can serve several functions including line-to-mic level matching (for your camcorder). Several companies make excellent mixers these days, but the one you want is the Mackie MS-1202VLZ. This is a truly professional piece of equipment that will last through many years of abuse. Not only is it a high-quality microphone mixer, but you can use it back in the edit suite to adjust audio levels, sweeten narration tracks and blend music. Not bad for a list price of $429 (even cheaper on the street).
If your camcorder contains a headphone jack, you should also invest in a pair of headphones. These can be a simple lightweight model or a professional model, just remember – you get what you pay for. It should also have the same size headphone plug as your camera. There is nothing worse than a missing adapter just before a shoot. The function of headphones is simply to ensure your microphones are working properly and the record level is set correctly (if you can adjust it). Some camcorders feature a small speaker on the left side so you can listen as you use the viewfinder. This is handy for making sure the mic works, but it can’t do much else. Headphones allow you to check for hum and buzz in the microphone(s) and stop potential problems in their tracks. You can also use them with your new microphone mixer!
MICROPHONE ADAPTER FOR SHOESTRING BUDGETS:
Here is how to build a simple, inexpensive adapter cable you can use to plug one professional microphone into your 1/8" microphone jack. Disclaimer: This is not the "right" way to attach a mic to your camera, but it will work fine in most cases. You’ll need three items: one (1) three-conductor female "XLR" type connector (RS #274-011), 20′ of two-conductor shielded microphone cable, and one (1) 1/8" shielded stereo mini-plug (RS #274-858).
Plug in your pencil soldering iron (not gun – too hot and clumsy) and carefully strip back about 1" of cable jacketing for the XLR connection. Pull the guts out of the female XLR and slide the shell over the stripped end of the cable. Fold back the shield conductor(s) and strip 1/4" of insulation from the two center conductors then solder the light-colored wire to pin #2 of the XLR and the dark-colored wire to pin #3. Twist the shield wires together to make one conductor and solder it to pin #1 (make sure there are no loose wire "hairs" touching any other connections). Now you can slide the shell back up onto the connector and snug up the screws. Alternatively, you could buy a pre-made XLR microphone cable and cut off the male plug (RS# 33-4002).
Now for the fun part. Disassemble the 1/8" plug and remove the spring in the end (there won’t be room for it and the cable too). Slide the shell down the cable, carefully strip away 1/2" of the cable jacket and fold back the shield wires. On the 1/8" plug, squeeze the tip and ring solder tabs together and spread the cable clamp apart. Strip 1/8" of insulation from the light colored conductor and all the insulation from the dark colored conductor. Solder the light-colored conductor to the tip and ring tabs, making sure solder flows across both connections and the wire. Twist the stripped dark-colored wire together with the shield wires and neatly solder them to the ground connector/cable clamp. This can be tricky for two reasons: If you solder to the inside of the cable clamp, there must be plenty of clearance between the shield wires and the tip/ring connection. If you solder on the outside of the cable clamp, you should flatten the wires as much as possible to allow clearance for the connector sleeve. Trim any excess then gently squeeze the cable clamp on the jacket, slide the sleeve up to the connector and carefully thread the sleeve on the connector.
If all went well, you have an inexpensive solution to a widespread problem. You can use your new adapter to connect any professional microphone – handheld or wireless. Just remember that we have cheated with this adapter. There is no provision for impedance matching or an isolation transformer – all of which are included in the commercially available adapters. You should also treat the adapter with care – especially at the camera end. Don’t leave the wire dangling where you can trip on it. You don’t want to repair the mic jack in your camera! I have used this type of adapter for several years on a number of different cameras – all with great success. Enjoy!
• Audio For Video Part 2
• Audio For Video Part 3
c 1998 Hal Robertson ALL RIGHTS RESERVED
HAL ROBERTSON is an 18 year pro-sound veteran and owns Sound Foundation. A consulting/training firm specializing in media production.