Issues & Answers
Audio for Video Troubleshooting
Remember Murphy's Law? The generally accepted version is: "If anything can go wrong, it will go wrong and at the worst possible moment." Similarly, you may experience audio challenges in your video projects at inconvenient times. With planning, you can often anticipate problems and avoid them before they occur.
Here are some common ones, along with possible solutions.
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| Buzz, hum, crackle and other noises | An electrical problem somewhere in the system. | Buzz or crackle – Usually a loose ground wire Hum – Unbalanced cables near light fixtures , power or loudspeaker cables. Move the cable around until the noise stops – or – better yet, use an in-line transformer which converts the signal to a balanced low-Z configuration. Plug the mic into the balanced mic input or use another transformer to convert the signal back to high-Z to match the equipment’s input. Make sure the transformer is as close to the mic end of the cable as possible. (Don’t place the transformer at the mixer input – it won’t make the mic more resistant to electrical noise.) |
| Distortion | "Clipping" – likely a component in your audio chain is overloaded by a signal that is louder than it can accommodate. | Once the signal is distorted there is no way to remove the distortion with another device further down the chain. If the signal level from the mic is too high for the mixer, you need to turn down that channel's input level control on the mixer. If the range of adjustment isn’t wide enough, you can use an attenuator (also called a pad), which reduces the signal level from the mic without altering the sound. |
| "Tin Can" Sound | This can happen when the microphone is too far away from the sound source. The more reverberant the room, the closer the mic must be to obtain good sound. It can also be caused by phase cancellation, which happens when the same sound waves reach more than one mic at slightly different times. | If the problem is distance, move the microphone closer to the talker. If the problem is phase cancellation or "comb filtering", it can be avoided by following the 3-to-1 rule. What is the 3-to-1 rule? Find out here. |
| Popping and Wind Noise | Popping is cause by "plosives" –sounds at the beginning of a word that strike the microphone diaphragm and cause a thumping noise. Wind noise is pretty self-explanatory and is more common with condenser microphones. | To alleviate popping, make sure the microphone is at least 6 inches from the talker’s mouth, and experiment with positioning. Plosives from the letters "P" and "B" tend to travel directly outward from the mouth, while plosives from the letters "T" and "D" tend to travel downward (especially troublesome with lavalier mics). A foam windscreen is also helpful. For wind noise, the only solution is to use a foam windscreen and in extreme conditions, a "blimp" type windscreen like the ones you might find on shotgun microphones. |
| Vibration Noise | This low thumping sound is generally the result of someone banging or tapping on the stand or lectern where a microphone is mounted. | It can be reduced through the use of a shock mount. This is a special mounting bracket for the mic that uses rubber or elastic to isolate the mic body from mechanical noise. Boundary microphones can be mounted on a sheet of neoprene or thin foam rubber to improve isolation. |
| Feedback | This loud squeal is usually caused by a combination of several things – speaker volume, placement of mics and loudspeakers, and room acoustics. | Adjust these elements: mic placement, loudspeaker location and loudspeaker volume. Consider microphone polar patterns. Try:
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According to Shure’s own Chris Lyons, who contributed a great deal of content to this issue: “If you notice the sound, there’s something wrong with it”.
Anyone who has done a fair amount of recording will tell you not to try to “fix it in the mix”, or in this case, the final edit. Plan ahead. Think about who and what you are planning to record. Consider room noise, or if you’re outdoors, wind and weather conditions. Make sure you have a few microphones to choose from and double-check your cords and cables. Have back-ups on hand. Take the time to record rehearsals, experiment and listen. If you’re shooting a once-in-a-lifetime opportunity – a featured speaker or panelist, for instance – you’ll want to proceed with confidence.
Remember, every filmmaker had to start somewhere. You could be the next Lucas, Spielberg or Scorsese.
Resource Room
For a more comprehensive discussion including specifications on Shure Mixers, Microphone and Accessories for Video Applications, you can download a PDF copy of our "Audio Systems Guide for Video Production" by clicking here. Included in the booklet is a helpful reading list of additional resources on the subject.