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MUST SEE VIDEOS • Camcorder Selection for Audio
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Location Audio Principles • Signal-to-Noise • Managing the job • Location
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Transcript
Optimizing signal-to-noise for capturing good audio.
Signal-to-noise ratio is the fundamental principle in capturing quality audio. Let’s start with an example. Say, we’re in the car and listening to the radio. We’re driving down the street at 20MPH. The road noise is relatively low, and the signal is at a comfortable level. Things sound great. Now, we merge onto the highway. The road noise at 60MPH is much higher. So, what’s the first thing that we do … well, we turn up the volume on the radio. So, now we have a good signal to noise ratio again. But now, everything (road noise, radio volume) is just at a higher level.
Now, let’s say we have really crappy reception from the radio station. There’s lots of crackles, and the signal to noise from the radio station itself is very poor. If we turn up the volume on the radio, we don’t improve the signal-to-noise ratio, like we did in the previous example. We just get louder crap.
Now, let’s think about signal-to-noise ratio with the use of microphones. Say, we’re in a room with a lot of echo, and the microphone is very far away from the source. The signal-to-noise (echo) ratio is poor. But, if we move the microphone close to the source, now the signal is much higher than the echo, so we now have a good signal-to-noise ratio. We accomplished this, just by moving the microphone closer.
Now, say that we’re using a shotgun microphone mounted to the camcorder, and we’re doing an interview. All of the background noise behind the subject will go straight into the sensitive end of the microphone. So, the signal-to-noise ratio is not very good. And, if we turn up the volume or use a more sensitive microphone, we don’t improve the signal-to-noise ratio either. It just makes the crappy sound louder.
Now, if we boom the subject from above with the shotgun microphone, we will reject the background noise. Plus, the microphone is closer to the subject, increasing the signal level as well. So, booming the subject with the shotgun microphone is a win-win for signal-to-noise ratio.
So, the signal-to-noise ratio at the microphone input is key. Increasing the signal level going into the microphone relative to the ambient sound always increases signal-to-noise. So, GET THE MICROPHONE CLOSE. If the signal-to-noise ratio going into the microphone is poor to begin with, then increasing the gain behind the microphone will not improve it. (Note. The use of low noise preamplifiers to improve signal to noise ratio is a different principle. Low-noise preamplifiers can be used behind the microphone to take the place of noisy gain coming from the camcorder amplifiers. This does improve overall signal-to-noise).
Optimizing the signal means GET THE MICROPHONE CLOSE. Also, you must use a mic with a wide enough acceptance angle for the subjects you are trying to pick up.
Then, you must minimize the noise. Noise sources can be echo, electronic noise, AC vents, fluorescent lights … and even your camcorder tape drive. Techniques for reducing the noise would be to get the microphone away from the source of noise. Also, use the correct microphone type. Tuck sources of noise into the portions of rejection from the microphone polar pattern. And of course, use a juicedLink low-noise preamp.
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A walk through of real-life examples to understand the principles of signal-to-noise.
Related Videos: • Distance/Orientation of mics |
