Sound For Film and Video: The Importance of Getting Good Audio
How many times have you sat down to watch a video or budget movie, only to find that the camera work and picture editing is great, but that the sound is so bad it takes your attention away from the picture? You might even stop watching it altogether, or at least turn the sound way down. Watching a TV show, video or film should be a “complete experience,” where the picture and audio combine to produce a meaningful and well balanced whole.
However, it has often been the case that in television, cinema, and especially in amateur or semi-professional productions, that the sound has been seen as secondary to the picture. I don’t believe it should be that way. People will often put up with mediocre picture if the sound is good, but good picture with poor sound may see the ‘off switch” flicked by many viewers. So let’s set about giving a bit of an outline as to how you can go about acheiving good results with your audio.
Use A Separate Recording Device
‘What is wrong with recording sound using your cameras built in mics’ you ask? Well generally the quality of the built in mics and preamps in a camera is pretty average. Cameras also can have tapes or hard disks running, and other electronics that make noise which can often be picked up by the microphones. Another drawback is that to get good sound recordings, you may need to be closer to the source than the camera will allow while maintaining the right picture perspective. The best solution is to use a separate audio recording device, that is away from the camera. Many portable recording devices have built in microphones that are far superior to camera or camcorder mics. You could use the built in mics of the recording device and get better results than your camera mics, but a still better way is to use a separate microphone (or multiple mics) plugged into a portable recorder to capture sound. At a pinch you could mount a video mic to the camera, and record the audio that way. It should give you better results than the built-in camera mics, but still not really up to the standard of dedicated audio recorders and microphones. Cameras often use mini-jacks for plugging in microphones. Some smaller portable sound recorders also use this type of plug. The connections of these can be a bit unreliable, sometimes working lose, pulling out or crackling with movements. The best devices generally have XLR inputs, which lock the cable in place, and provide a much more reliable connection. Larger professional cameras normally use XLR inputs. Microphone signals are of a very low voltage, and require preamping to bring them up to a useable level. Sometimes as much as 60 or 70dB of gain is required to do this. It is important to have quality preamps in order to do this well. Poor preamps can add noise, distort signals, and generally do nasty things to the sound! Many cameras have very poor onboard preamps. A good portable recorder will have far better preamps than those found in a camera.
Another thing to consider is that audio metering in cameras is often poor, and also it’s hard to monitor these at the same time as concentrating on filming. Automatic Gain Control is also something to be avoided if at all possible, as it can introduce compression that may not be of the best quality.
A really high-end recorder like those made by Nagra or Sound Devices will have preamps that rival the best studio preamps in quality, but even quality lesser devices than these will generally better preamps than a camera. Try to use a separate recording device rather than the camera if at all possible.
If you have a couple of mics you can record them onto separate tracks in the recording device and mix these to suit later. Sometimes a field mixer (a separate device from the portable recorder) can be handy in the field where more than one source needs to be blended or mixed on the spot. However, recording everything to separate tracks if possible is going to give you maximum flexibility at mixdown later. Traditionally a field recorder and and field mixer were distinct devices,and the sound recordist carried both, but these days it is common to see devices that include both the recording and mixing functions in a single unit.
A Two Man Job
The answer to acheiving the best levels and quality of audio lies in having a second person, who is away from the camera, to be responsible for the audio recording. Their job is to monitor the sound, and not worry about having to concentrate on the filming as well. If you are really lucky you might even have a third person to man a boom pole, leaving the second person to just monitor the recording levels. The boom operator concentrates on microphone postioning. Unless it is an interview, news report, or a documentary style production, you don’t really want to see someone holding a mic or wearing a lavalier mic. To get clear speech you will want the boom operator to be able to get the microphone just out of shot above the voice. Operating a boom pole is an art in itself. The difference in level between whispering and shouting is huge, so someone needs to have eagle eyes watching the metering at all times for best results. Especially since we are not using AGC (automatic gain control). That’s the job of the person reponsible for the audio recording. Some recording devices have good limiters to catch rogue peaks before they clip, but some other devices have lousy limiters where you can hear the sound truncating abruptly. Manual gain control and/or light compression usually gives more natural results. However, compression is best left to someone who is experienced and knows what they are doing. Novices should probably not try to use compressors while recording, as the results of poor compression can’t be undone. Set levels manually, and if you have a limiter of a known high quality, you could use that to catch any extreme transients. If a limiter is being triggered constantly the results will not be pleasant. Backing off the gain will produce more natural and pleasing audio than sound that has been heavily limited or compressed.
What Type of Microphone should I Use?
In most cases for use in location recording a directional shotgun mic mounted to a pole is the best option. There are a number of models of shotgun microphones available, ranging from relatively cheap, to very expensive at the high end. The Sennheiser MKH416 is the traditional standard mic here. Rode Australia makes some good model shotgun mics for those with a lower budget. The mic can be plugged directly into your portable sound recorder if it has in-built mic preamps. Shotgun mics are very directional and have good rejection of sound to the sides. You will need some kind of shockmounting to prevent handling noise, and if outdoors some sort of wind protection as well. Low rumbles and wind noise can really marr a recording. A blimp or zeppelin style shockmounted microphone enclosure, covered with a fluffy fur type windjammer is ideal for outdoor shoots. A foam windsock alone over a microphone capsule is not sufficient to block out wind noise and rumble. For recording general of atmos and ambience, as well as shotgun mics, fixed polar pattern (such as cardiod) condensor mics can be useful. If you want a stereo atmos sound there are various ways to position mics for this, but I won’t go into those here. An example would be an X-Y pattern. I find small diaphram condensor mics handy for this. Special stereo mics are also an option. If your recorder has onboard stereo mics of sufficient quality you may even want to use those.
Sync’ing Video and Audio
Recording of picture and video separately requires some way of sync’ing otherwise it will result in a shambles. If you have multiple cameras and an audio recorder, you will need to be able to keep these perfectly sync’ed so that you can align them during editing. The simplest way to do this is to use a clapper board, or someone using a single handclap in view of all the cameras, and with the audio rolling in record. It is important that everyone can see the clapperboard or hand clap, and that there is only a single clap at the start of each recorded clip, to minimize the risk of confusion as to the start of the cut. It will then be easy to align all the audio tracks and film in the edit suite. A clear procedure of ‘calls’ that everyone on the shoot is familiar with is essential to maintining an orderly shoot. Traditionally in film an asistant would call “turnover,” at which point the sound recordist would call back “speed” once he had hit the record button. The camera operator starts his camera rolling and calls “turnover,” and the sound recordist replies back “speed,” before the cameraman calls “mark” for the clapperboard to be clapped. Then the dirctor calls “action”. In our case, so that everyone knows all devices are in record, we should follow a similar procedure. I prefer to use terms words like “roll sound” or “roll film”, and having worked in television, I am much more used to the term “cue” rather than “action”. Whatever words you use, make sure that everyone involved is clear as to their meaning. It’s also a good idea to take notes on each scene that could make things easier later when editing. This is Known as “slating.”
The recording of picture and sound and their syncing on a location shoot using type above method should work well in most situations, though it is possible for small drifts in timing that may require correction due to the different internal time clocks of all the devices. If you are using analog tape or film it is most likely to be noticeable. Our clapperboard only gives us the beginning point of our film, and so that is our main reference, but nothing solid as timing reference from there on in. In television or larger film productions, a method of time aligning using time code is the norm, where everything is sync’ed to one clock, keeping things tightly aligned frame to frame, throughout the record process. SMPTE/EBU timecode uses a string of eight numbers that make everything easily identifiable on a timeline. The numbers are hours, minutes, seconds and frames. For example 03:24:37:16 read on a timecode would mean three hours, twenty-four minutes, thirty-seven seconds and sixteen frames. The hours are in 24 hour format, the minutes and seconds as normal from 00 to 59, and the frames from 00 to 29. It is not within the scope of this article to go into depth on understanding timecode, as it can be quite complex to understand and deserves it’s own separate explanation.
In the Editing Suite
Once we have our video and audio recorded and we get them back to our editing software, we need to align the “clap” from each camera and audio track to give the start point of the clip. Cut all tracks at the point of the initial transient of the handclap and work from there. Go to the end of the take and check to make sure everything is still aligned there too. Hopefully it will be. If a single timecode clock has been used it almost certainly will be. However, if we have not used timecode, and just the “clap” method, if it has been a long scene, it is possible that timing errors may have crept in. If you find further along that sync has slipped, try to find a clearly identified event further into the scene, and cut and re-align here. Plosives sounds such as “B’s” and “P’s” can be good because they are clearly visible in the audio, so you could use them as your reference, so long as the person speaking is also clearly visible in your picture. Sounds such as “p” and “b” should occupy only one frame, which should make re-alignment relatively easy. Otherwise you will need to find another clearly evident transient in the sound that is also clearly visible in the picture, and use that for aligning.
As you can see here I am passionate about sound and I get irritated by poor sound in video, film or television. Sound quality in youtube is often even worse. Let’s all do our part to improve things. I hope in this article that I have given you a few basic ideas to get you thinking about improving the sound of your next production. Your aim should be to give the viewer a good listening and viewing experience, or one that doesn’t distract them from the topic if it’s a documentary or similar. So don’t cut corners and take short cuts with your audio if at all possible.
By Tony Koretz
© copyright 2011