HDSLR, small format digital video camcorders and pocket digital audio recorders are being used ever increasingly for professional application. In addition, there are still those rare occasions when we encounter the older video formats, such as mini DV, Digital 8, Hi8mm, and even SVHS.
The various merits of shooting images with these relatively inexpensive, unobtrusive, and extremely portable video acquisition systems are familiar to most readers. However, interfacing these consumer and prosumer camcorders with professional audio can be a nightmare.
For example, when you use the consumer shotgun mic that came with the camera (or was sold for it as an aftermarket accessory), the audio sounds clean. Not great, but free of excessive static and electronic residue. However, when you try to plug in your thousand dollar professional microphone, the result is a lot of buzz, hum, and lower audio levels. Why should better equipment make more noise than the cheap stuff that came with the camera?
Let's examine why this happens and how to fix it.
Most camcorders will readily accept the industry standard 250 ohm low-impedance microphone input signal, so the problem is not that of matching impedance level so much as it is a question of proper input cables. Purchasing an impedance matching device is not the solution to your problem, even though the salespeople at consumer camera outlets will try to convince you that it is. Trust me, it is NOT about the impedance.
The mic input for these consumer camcorders is generally a 3.5mm (aka 1/8 inch) stereo mini jack. The output of a professional grade microphone is XLR 3-pin. Therefore, the first task at hand is to adapt XLR 3-pin output to mini stereo input. To do that, we need an adapter cable that consists of a female XLR 3-pin connector at one end feeding a mini stereo plug at the other.
Since the camcorder input is stereo, our adapter cable needs to split the incoming monaural audio over both the left and right camcorder channels. If we were to record onto only one channel, we risk serious damage to our soundtrack.
The second, empty, channel would fill with hiss and noise. When our audio is transferred from analog video for post-production, a percentage of this noise will most likely bleed into the good channel. Such is the nature of consumer audio/video, due to the proximity of the recording circuits and head placement.
Some lower end digital devices also suffer from track bleed, though not as much. It depends on the quality of the electronics and the physical separation of the wires & components.
In addition to audio bleed, the presence of an empty track may cause confusion or even havoc with the automatic gain control in the camcorder. Even those cameras that offer a manual audio level control will revert to auto gain if the power is turned off, tape changed, or battery changed. Unless you are meticulous, the resumption of video recording may be with auto gain ON.
Finally, recording to just one camcorder channel makes it difficult to monitor some meter levels and to hear with both sides of the headphones (unless you use cumbersome adapters with your headphones).
Bottom line: Always feed the Left and Right camcorder channels, either with monaural audio going to both sides, or with discreet stereo audio going onto respective Left and Right. Never assume that what is on the second channel will not show up in some form on your first channel, so be very careful if recording wild questions or cue tracks that you plan on editing out.
The wiring of this basic adapter cable must be what is referred to in the industry as dual mono. What this means is that the main audio signal (pin 2 of the XLR connection, the audio POSITIVE signal) is routed to BOTH the tip and ring of the stereo mini plug. The tip and middle ring of the stereo mini plug represent the main (audio positive) signals for the Left and Right channels. Pin 3 of the XLR connector, which represents the negative audio signal) along with Pin 1 of the XLR connector (which represents the ground signal) are both wired to the remaining sleeve (lower shaft) of the stereo mini plug.
The effect of this dual mono wiring scheme is that the audio from the XLR input is distributed equally to the Left and Right channels.
In contrast, if you were to find an XLR to STEREO mini adapter that was traditionally wired so that Pin 2 of the XLR went to Tip, Pin 3 went to Ring, and Pin 1 went to Sleeve – the results would be disastrous. The output from the XLR (mic) would be halved, with each half going to Left or Right. However, the signal going to the Right channel would be out of phase with the Left Signal.
You might not notice it during live production in the headphones, but when you process the audio later on, you could have some very serious cancellation between the two tracks. (One solution would be to disconnect one channel in post so that it did not cancel or interfere with the remaining one.)
Visually, a conventional XLR to stereo mini cable looks identical to a dual mono version. You cannot tell one from the other without using an electronic cable checker or VOM meter. Therefore, it is extremely important that you know the source of the cable: never just grab one that was laying around. Be certain that it is designed for camcorder application!
What about the buzz?
Earlier in this article we mentioned those aftermarket microphones that the consumer manufacturers would so dearly like us to invest in. Most of those mics are of the electret condenser design, meaning that they need to see a few volts of DC power in order to function.
To power these mics, the camcorders produce three to six volts DC at the mic input jack. Even those camcorders that have a separate DC OUT micro jack alongside of the MIC INPUT jack, still root the DC circuit in the ground of the MIC jack. Unless your plug-in mic is of the precise electronic formula of the camera maker, you may experience symptoms of DC interference.
Depending on the particular characteristics of your pro mic, these DC related symptoms may include: non-existent audio; a significant loss of gain/volume; buzz/hum; or even intermittently increasing buzz/hum. If you barely jiggle the stereo mini connector, you may even hear sharp crackling, as if there was a broken wire. Different types of mics react differently.
To eliminate this buzz problem, the upstream DC voltage must be blocked by means of capacitors. Choose your capacitors wisely, for too little will not cure the buzz, and too much will affect the mic signal.
There are a few companies that manufacture custom adapter cables with internal capacitors, but not many. If you ask your local supplier and they are not sure whether or not their adapter cables are of this special variety, chances are that they are not.
Bear in mind that not every camcorder requires the DC blocking. Earlier Sony cameras were notorious for DC issues, but Panasonic and JVC were generally okay. Canon cameras varied; some needed the DC blocking and some did not. The newer Sony cameras seem to be okay and no longer require the DC blocking.
But if you are not sure, or will not have an opportunity to test the connections, then having an adapter with DC blocking cannot hurt. There is no downside, other than price, for using a deluxe adapter cable with the DC blocking with all the cameras.
Street prices for simple, dual mono adapter cables range from $15 to $50. Price will vary depending on quality. Deluxe cables with DC blocking may cost from $60 to $100.
Tips on Using the XLR to stereo mini adapter cable
The basic XLR-DV cable is a short adapter that features one female XLR 3-pin connector at one end and a right angled mini stereo plug at the other. It is wired dual mono so that audio is distributed properly over the left and right camcorder channels.
Deluxe versions of this cable feature blocking capacitors housed inside of the shell of the XLR knock out the DC interference.
We recommend slipping a rubber band around the mini connector and pulling it around the camera body like an oxygen mask, thus applying inward tension on the connector. The XLR connector of the cable should be strain relieved by tying or taping it to something sturdy on the camera body, such as the strap lug.
Never allow any long cables or any weight to tug directly on the mini jack of the camcorder; the jack is fragile and can loosen or damage easily. For that reason, we do not recommend purchasing an adapter cable longer than what it takes to reach the camera mounted shotgun mic or just the wrist strap (if you are using audio from a mixer or boompole).
Make sure that the XLR input of the adapter cable is secure, and that there is minimal tugging on the delicate stereo mini connection.
If you need to feed audio via a longer cable, then use a regular XLR to XLR mic cable, and plug it in to the XLR input of the adapter. But do not make the mistake of trying to use a real long adapter cable!
Audio Adapter Boxes
For many people, the better choice would be to use an Audio Adapter Box rather than a simple adapter cable. Audio Adapter Boxes usually mount securely under the camera body, although some models offer a belt clip and extender cable so that the box can ride on the camera operator’s belt.
I find that affixing the box underneath the camera is fine when you are tripod mounted, or when the shotgun mic is riding atop the camera ENG style.
Should you go handheld with the camera, and taking an external audio feed, it is better to secure the adapter box to your belt. That way, any tugging on the mic cables are absorbed by your torso rather than jerking against the camera.
Another advantage of adapter boxes is that they offer more flexibility of inputs. Most boxes have two XLR inputs, and either one can be switched for mic level or line level input. In addition to the switches, each input has a volume control that can lower the incoming volume (but not raise it). Some boxes also offer a choice of grounding modes, so that they can be used with a variety of cameras. All of the boxes that we have tested feature some sort of DC blocking, either capacitors or transformers.
There are some more elaborate adapter boxes on the market that even feature microphone pre-amps similar to a mixing panel. These pre-amps allow you to raise the volume as well as lower it. Some even provide remote Phantom power for condenser mics, and visual metering of audio levels.
The Sign Video model XLR-PRO, is an adapter box that mounts beneath the camera body. It features two XLR inputs for mic/line, mono/stereo, selectable ground, and volume controls. A belt clip and extension cable are included, so that you have the option of either wearing the adapter or mounting it to the tripod leg. Price is around $160.
BeachTek makes a whole lineup of XLR box that fasten underneath most camcorders and provides two XLR mic/line inputs, volume controls, and output is a stereo mini plug that connects to the mic input jack of the camcorder. Prices start around $179 for the basic models. They offer different configurations (sizes) for a variety of cameras.
BeachTek also offer deluxe models such as the DXA6 which features 48volt Phantom powering for condenser mics. And their DXA8 has actual mic pre-amps that allow you to RAISE mic volume.
Studio One is yet another manufacturer of adapter boxes, most of which are intended to be belt worn. They even offer boxes with three XLR inputs.
JuicedLink makes some sophisticated two and four input boxes that are essentially small mixers. They are a newer player in the game, and address the needs of cameras that appear to have been designed with all attention given over to picture quality and very little attention to audio.
Whirlwind Audio also offers a nice, inexpensive adapter box that uses Neutrik Speak-On connectors that accept ¼-inch as well as XLR inputs. However, you do need to supply your own min to mini adapter cable to go from the box to your recording device.
Line Level Audio Feeds to Consumer Camcorders
Audio coming from a mixing board is usually at 600 ohm line level, which is a much hotter and stronger signal than mic level. Although the better cameras on the market have selectable inputs for mic level or line level, the standard consumer camcorders only accept mic level external input when used as a live camcorder; when the camcorder is used as a DVR it will accept external line level video and external line level audio via RCA jacks. When the camcorder is functioning as a camcorder, the RCA line level inputs are disabled.
Therefore, to feed line level audio into a simple camcorder (which is mic level), we need to reduce the signal by 30 to 50 dB. The 50 dB setting is technically the correct one to use, but in the real world there is some latitude.
Some portable mixing boards have a switch to reduce their outputs from line to mic level. You can't ask for more convenience than that!
Otherwise, one needs to insert a pad or attenuator between the output of the mixing board and the input of the camcorder. Shure makes a 50 dB line to mic Attenuator. Audio Technica offers a switchable -10, -20, -30 dB pad. HOSA offers a –20 dB, -30 dB, -40 dB switchable pad. Any of these devices will work, since the camcorder input does offer some range with its onboard gain or volume controls.
Sometimes when you feed from a mixing board, the DC interference at the mic input jack may be a problem. Sometimes it may not. It all depends on the design of the mix board.
To play it safe, use an input cable or adapter that features DC blocking. If the camera and the mixer both need to power from AC, try to plug them into the same power strip to reduce the chances of a ground loop.
So far, we have only discussed the logistics of getting an audio signal into the camcorder. Now, a few comments on what that signal should be.
There is an old computer programmer’s expression that goes "garbage in, garbage out." That applies to production sound, as well. It does no good to have a clean signal entering the camcorder if that signal is worthless to begin with!
Just because you are recording on an inexpensive medium is no excuse to be lazy with technique. Small camera or not, a tripod and lights will still make the difference between a home movie and a professional product. And proper microphone deployment and mixing are still essential if you want a professional sounding track.
Use the same mics and techniques that you would on a big budget show.
Mic your subjects from close overhead with a boompole, and use high quality ENG or full condenser shotgun mics.
If using lavaliers or wireless mics, pay careful attention to proper placement and rigging. Check for clothing and wind noise.
Adjust any cables that function as antennas. If possible, mount your receiver as close to the action as possible, any pay careful attention to antenna line of sight.
Mounting a radio receiver on a consumer camcorder can be tricky, since these cameras are not as well shielded as their professional large format counterparts. Camcorders tend to produce a lot of RF interference near their viewfinders and near the recording heads. Try moving the receiver around to find a "sweet spot" that is free of buzz or hum.
If your camcorder is equipped with an auto gain control, then your best strategy for eliminating or reducing the "hunt for some sort of noise to amplify" is to make sure that you feed a well mixed or well chosen signal to the camera.
Think of it in terms of working with a still camera that has auto light metering. Frame up on a high contrast or unusual lighting condition and you get horrible exposures. But compose a scene with some highlights, shadows, and a lot of middle tones and the exposure come out beautiful.
It's the same way with sound. Feed your camcorder a strong signal with dialogue dominating over ambience; or sound effects dominating over background noise -- and the resultant soundtrack will be fine.
By the way, a neat trick when you are recording in mono and using a camera with manual audio settings is to use a Y cable and bracket your exposure, so to speak. Split the monaural output to both XLR inputs, and offset the volume so that one track is better for soft passages while the other track is adjusted down for the louder stuff.
In conclusion, using a cheap camera is no excuse for cheap sound. Do it right, and your audience will never know if you shot with a professional rig equipped with XLR inputs, or a consumer rig that everyone else believed was limited to the dinky plastic mic that it came equipped with.
