Audio Basics: Microphone principles and types

cc licensed flickr photo shared by State Library of Queensland, Australia

Microphones along with speakers are some of the oldest components in the history of audio dating back to Alexander Graham Bell and the invention of the telephone in 1876.

Below is a video which provides an overview of the basic types of microphones and their history.

All microphones are analogue devices in that they convert mechanical pressure waves into analogues electrical waves, these can then be amplified and digitised.

In an educational environments the condenser and to a lesser degree the dynamic microphone are the most common varieties utilised. These come in various guises.

Microphone Headsets - analogue

Analogue headsets are commonly used with computers and are referred to as analogue because the computers sound card does the digitising of the electrical waveforms generated. Like all small form factor "electret" condenser mics they require 1.5 - 9 volt power to operate, this is supplied by the computer microphone socket. Most PC computers supply this phantom power however most Apple Mac based computers do not so will not operate if plugged into the microphone socket.

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cc licensed flickr photo by sridgway:

Typically analogue headsets have 2 leads, one for the microphone and one for the headphones which are plugged into the computers sound card. The leads follow a loose colour coding convention which is unfortunately not often adhered to, pink for the mic and green for the headphones. They may also have printed symbols which denote the microphone and headphones. One of the common problems is that they are plugged into the wrong sockets on the computer.
They commonly have an in-line volume control and a microphone mute switch which is also a good place to check if you have no audio signal. The microphones fold out and need to be close to your mouth, 15 cm max to work effectively.

It is also common for microphones to be referred to as noise cancelling, designed to filter out ambient or background noise from the input prior to recording. This technique uses two microphones and circuitry to remove the noise. The primary microphone, situated close to the users mouth is combined with the signal from the second mic, pointed away from the user, in such a way as to cancel out the noise.

Analogue headsets range anywhere from $7 up to $50 depending on the quality of the headphones mostly and are the most common type of headset used.

Microphone Headsets - USB

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cc licensed flickr photo by sridgway:

USB headsets are fully digital in that the headset itself converts the analogue "electret" condenser microphone signals to digital information and hence the sound card in the computer is not utilised. The data is transferred via the USB port. One of the great features of USB headsets is that they are "plug and play" and don't require any drivers to be installed and will generally be ready to use once the operating system has detected and configured the headset. The advantage of USB headsets is that you bypass the common issues surrounding sound cards and drivers, all you need to do is plug the lead into a free USB port and ensure the microphone level is set appropriately in the sounds and audio devices panel.

Condenser Microphones

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Condenser or capacitor microphones as they are sometimes referred to are more commonly seen in recording studios or radio stations however with the rise in popularity of podcasting condenser microphones have increasingly become the choice of those who wish to move the quality of their recordings up a notch. They typically require a mixer which provides the 48 volts required to power the microphone and amplify the signals. At the high end they are very sensitive and require custom microphone stands used in sound proof rooms however they can come in the form of hand held microphones used to do mobile voxpop interviews. In recent times they have reduced in price making them an affordable choice for educators.

Dynamic Microphones

cc licensed flickr photo shared by Brendan Biele
Along with being one of the oldest types of microphones dynamic microphones main distinguishing features are being robust, water resistant, not requiring phantom power and being well suited to high noise level environments such as live stage music. They are frequently used as portable compact microphones for interview recordings and table microphones for recording live speakers.

Wireless Microphones

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Wireless microphones are commonly used in the audio industry where speakers or performers are frequently moving around and a wired solution would be inconvenient. Typically they comprise a battery operated transmitter unit which is worn or held by the speaker and a remote receiver unit which picks up and amplifies the audio from the wireless microphone. They are an essential item where presenters wear a wireless lapel microphone while a roving wireless hand microphone is used to capture audience questions and answers. The output from the wireless receiver is generally an analogue signal which can be fed directly into a computer or a portable digital recorder.

Choosing the right microphone

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Talk to a podcaster and they will tell you that they have a bag full of microphones ranging from the cheapest "electret" condenser mic they started with right up to their beloved studio condenser mic fitted with a pop screen :> A significant component of achieving quality final audio resource is begin with a high quality recording hardware compensation and post production software filtering can only go so far in repairing a poor quality recording. Selecting the appropriate microphone and using it appropriately for the context is paramount in achieving a quality recording. Think and consider the following factors and choose your microphone and setup to suit your context :-

  • What is the environment for the recording, a quiet room? a noisy background? 1 or a group of people ?
  • always make sure your speakers are near a microphone to be heard effectively
  • If your speaker is moving consider a wireless lapel microphone
  • If there is an audience and who will ask questions use a roving hand microphone
  • ensure your speakers are aware of the recording, microphone placement and the need to use it
  • are multiple audio sources involved? do you need consider microphone placement?
  • live monitor and test your audio prior to recording, are the levels sufficient and the signal to noise ratio high enough?
  • consider recoding 1 min of pure environmental background noise with the mics turned on. This can be used later as a noise profile to remove the noise such as air conditioner drone.