- Written by Paul Terpstra, Klover Products
In Part 1 of this series, we discussed the importance of isolation, or emphasizing the desired audio as compared to the ambient noises.
In Part 1 of this series, we discussed the importance of isolation, or emphasizing the desired audio as compared to the ambient noises.
Hands down the most over-looked element of any television production is the audio.
Live productions such as sporting events present many challenges but one of the most daunting is providing good audio for your production.
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Whether you are producing a commercial, infomercial, corporate video or even episodic television, you’re going to need to know how to record the human voice.
If your speaker (audio source) is moving around a stage a cable could be a big problem. While wireless microphones provide many benefits including mobility, there are challenges as well.
a. Is your subject willing to hold a microphone or wear a transmitter on their body? Very few wedding couples want to hold a microphone during their ceremony and most brides will refuse to wear a transmitter under their wedding gown.
b. Will the batteries last for the duration of your event? Even news casters deal with this. Batteries die at the worst possible moment.
c. Will there be a number of different wireless microphones in the same venue? This can lead to radio interference that can ruin your audio.
d. If using a wireless handl-held microphone, will speaker be able to keep from placing his hand over the antennae?
Microphone with a cable avoid the technical challenges that wireless microphones face but the cable creates other challenges. A hand-held, or stick microphone, with a cable often creates a tripping hazard if the speaker is walking about. Speakers that are stationary can used lapel or over-the-ear microphones but face the risk of pulling off the mic or pulling out the cord if the speaker walks off before disconnecting the microphone.
Do you want to capture one speaker or several? Do you want to focus in a single bird or capture the sounds of the wildlife all around? These types of questions determine the pickup pattern (or polar patterns). There are a wide variety of articles on polar patterns available from all types of sources. One of our favorites is written by Caleb Ward for PremiumBeat.com. (https://www.premiumbeat.com/blog/6-microphone-pickup-patterns-every-filmmaker-should-know/)
Another good article written by Paul White, is also located on SoundOnSound.com. (http://www.soundonsound.com/techniques/using-microphone-polar-patterns-effectively) We especially appreciate the articles explanation that “polar patterns aren’t always as simple as they first appear”. People often neglect the audio that is captured from the sides and the rear of shotgun microphones but it can cause serious problems if someone begins speaking directly behind a shotgun microphone. If you are a fan of shotgun microphones, you might find this article to be very interesting. (http://www.soundonsound.com/sound-advice/q-how-do-shotgun-mics-work)
The point is this, if you are trying to capture several different speakers, or a quartet, you will want to use a cardioid or an omni-directional microphone. However, if you want to focus in on, or only capture, a single sound source such as a single person in a noisy room, you will want to use a microphone with a supercardioid, hypercardioid, or even a lobar polar pattern.
A pattern that you won’t find explained in many articles is the conical pattern that a parabolic microphone provides. The conical pickup pattern typically extends 15 degrees off of the center axis of the parabolic dish. Parabolics do pick up off-axis noise and some noise from behind the dish but usually much less than any other option.
How far away from the audio source is the microphone? Lapel, or lavaliere, microphones normally must be within in 6 to 9 inches of the speaker’s mouth to provide best performance. Hand-held, or stick, microphones usually need to be within 9 to 12 inches of the speaker to provide the best audio signal. While this is up for much debate, a shotgun microphone will normally need to be no more than 4 feet from a speaker to capture the best audio.
If you want to capture audio from more than 6 six feet away, you need to consider a parabolic collector. Parabolic collectors use a precisely shaped dish to focus all the sound energy from directly in front of the dish onto a single point. A standard electronic microphone is located at that focus point and the combination is referred to as a parabolic microphone. Small parabolic microphones, if properly designed, can capture dialogue from 30 feet or more in quiet situations. The large parabolic microphones you see at football games can capture dialogue from 500 feet or more in quiet situations.
In all cases, there are extenuating circumstances. The louder the environment the closer the microphone will have to be to create a stronger audio signal when compared to the ambient noise. The professionals call this a larger signal to noise ratio. This ratio determines how easy it is to distinguish the audio you want from the noises that you don’t want.
4. Frequency Response
Every microphone has a response curve that shows how it reacts to various audio frequencies. Every microphone will have a graph of the signal level at various frequencies. The curve will also show the highest and lowest frequency that the microphone will capture. A microphone than does not capture audio below 100 Hz, for example would be useless for music, or recording a bass guitar. (A sample response curve can be seen on this spec sheet from Sennheiser https://en-us.sennheiser.com/global-downloads/file/812/MKE_2_4_Gold_C_GB.pdf)
For many microphones this signal curve is not a straight line. This means that some frequencies are captured at a higher level than others. For example, many lapel (or lavaliere) microphones have a range of frequencies that have a significantly higher signal than other. This range of frequencies with higher signal level is usually between 2kHz and 20 kHz. The change in signal level is not constant, however. It increases gradually to a peak and then falls off again.
Using a parabolic collector will also affect the frequency response of the microphone located within it. As higher frequencies reflect off of the collector dish better than low frequencies the parabolic microphone (collector and microphone) will have a response curve that shows a higher signal level at high frequencies and a slightly lower signal level at lower frequencies. It is a common misconception that parabolic microphones will have almost no signal below a certain frequency (related to the diameter of the dish and wavelength associated with the frequency) but this has shown to be untrue. We have demonstrated that a dish just nine inches in diameter can capture audio at frequencies well below the supposed thresholds. Capturing any human dialogue shows that this concept is invalid.
When trying to conceal a microphone size is obviously a major concern. A hand-held, or stick, microphone is hard to conceal unless the camera shot is extremely tight. A miniature microphone is the obvious choice. There are many varieties of miniature microphones available. These range from larger lapel microphones worn on the speaker’s clothing to tiny units worn over the ear or concealed in the speaker’s hair.
6. Intended Use
A factor that is easily overlooked is the intended use of the captured audio. If the signal from the microphone is being recorded there is more latitude in range and pickup pattern than if the signal is being used for sound reinforcement. By sound reinforcement we are referring to an amplifier and speakers. Feedback is the constant challenge for sound reinforcement, or loud speaker, systems.
The audio coming from the loud speakers can be captured by a microphone and re-amplified. That signal can be captured and amplified again. That cycle can be repeated many times if just a fraction of a second leading to the annoying squeal we have all experienced.
Proper location of the microphones and loudspeakers are the best solution to feedback. However, keeping the microphone as close to the speaker (sound source) as possible and using as focused pattern as possible will help to reduce the potential for feedback.
Parabolic microphones are very focused but their extreme range, or sensitivity, makes it challenging, but not impossible, to use them for sound reinforcement applications. Very low gains (amplification) must be used with a parabolic and they must be “aimed” to avoid reflected sound coming from the loud speakers.
It may seem obvious that moisture is a concern at an outdoor event but your microphones can also be affected by sweat. If you are using a miniature microphone wore on the lapel, or over the ear, or even in the hair, consider using moisture resistant microphones. Microphone manufacturers, such as Countryman Associates, are producing microphones that can operate submerged in water. (http://www.countryman.com/b3-omnidirectional-lavalier-microphone)
Paul Terpstra has more than 35 years of engineering and product development experience. He founded Innalytical Solutions, Inc. in 2004, to provide a wide range of engineering services including forensic engineering, Finite Element Analysis, electomechanical design, machine design, and machinery repair. Paul was recently granted his eleventh U. S. Patent.
In April of 2012, Paul and Patrick Santini, an Innalytical Solutions customer, created Klover Products, Inc. Previously in 2011, they had jointly dveloped a parabolic microphone for Fox Sports when Fox audio engineers grew disatisfied with the available products. That original test unit turned out to be the first prototype of the microphone that would later become the Klover MiK 26. The Klover MiK 26 parabolic microphones have been used exclusiely by Fox Sports for football broadcasts since 2012.
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The unique shape of the parabolic collector allows anything coming into the dish, that is parallel to the center line of the dish, to be focused onto a single point.
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