Home Recording Series Vol 3 – Microphone Basics
Welcome to part 3 of our Shure home recording series. This week, you will learn the basics of microphones to help you make an informed choice on your next recording. Your microphone is the first point in your signal chain, and so it’s essential you make the right choice for each application – a process that requires some foundation knowledge.
A microphone transducer converts sound waves into an electrical signal. The two most common transducer types are Dynamic and Condenser:
Dynamic microphones consist of a diaphragm, voice coil, and a magnet. The magnetic field surrounds the voice coil, which is attached to the rear of the diaphragm. The motion of the voice coil in this magnetic field generates the electrical signal corresponding to the picked up sound. Due to their simple construction, dynamic microphones are economical and rugged. They can handle extremely high sound pressure levels and are tolerant of extreme temperatures or humidity. For these reasons, dynamic mic’s are often favoured as live performance microphones, however, there are regularly used in the studio to record loud sound sources, such as guitar cabs or close mic’d drums.
Condenser microphones are based on an electrically-charged diaphragm and backplate assembly as a sound sensitive capacitor. When the diaphragm is set in motion through sound, the space between the diaphragm and the backplate is changed – this variation in spacing produces the electrical signal. All condenser microphones need to be powered, and this is usually provided by phantom power from your pre-amp.
Condensers have a higher output, wider frequency response and are generally regarded as studio recording microphones, however, for some live applications such as choir or drum overheads – condenser microphones provide the sensitivity and clarity required . As a general rule, for detailed, complex sounds such as vocals and acoustic instruments, a studio engineer will often prefer a condenser microphone for a more detailed and natural sound.
There are two main types of condenser microphones:
Small diaphragm – Called small diaphragm because the transducer’s diaphragm is less than one inch in diameter. Small diaphragm microphones provide a more natural sound reproduction and are preferably used for mic’ing acoustic instruments.
Large diaphragm – One inch in diameter or larger, large diaphragm microphones usually have higher output, less self-noise, and better low-frequency response, which can result in a “higher fidelity“ sound for both vocals and instruments.
The pickup pattern is the representation of the microphone’s directionality. In other words, the pickup pattern describes the microphone’s sensitivity to sounds arriving from different directions.
The most common pickup patterns are as follows:
An omnidirectional microphone picks up sounds equally from all directions and reproduces a more natural sound than unidirectional microphones. The disadvantage of an omnidirectional microphone is that they pick up all the ambient sound in a room, e.g. the computer fan, and therefore is often not suitable for home recording. However, if you want to pick up the general sound of a room or group vocal they are often the best choice.
This is the most common type of microphone and is called “cardioid“ due to its heart-shaped pick up pattern. Cardioid microphones are most sensitive at the front and is least sensitive at the back. This helps reduce pickup of background noise or bleed from nearby sound sources, and also allows you to take advantage of the proximity effect where appropriate (more on this soon).
Supercardioid microphones are more directional than cardioid. They have a tighter pickup pattern, further isolating the sound source. The drawback is they also have some pickup at the rear. When positioned correctly, they are good for noisy, crowded spaces and when multiple microphones are being used.
INFO: Proximity Effect
Every directional microphone (i.e. cardioid, supercardioid) has the so-called proximity effect. This is created when the microphone moves closer to the sound source resulting in an increase in bass response and, hence, warmer sound. Most notably when one is recording vocals the speaker or singer needs to pay attention to the distance of the mic as every change in the distance creates a difference in sound.
The frequency response is the output level or sensitivity of a microphone over its operating range from lowest to highest frequencies. Generally, two types exist:
Flat Frequency Response
All audible frequencies (20 Hz – 20 kHz) have the same output level. This is most suitable for applications where the sound source has to be reproduced without changing or “colouring” the original sound.
Tailored Frequency Response
A tailored response has varying output levels across the frequency range and is usually designed to enhance a sound source in a particular
application. For instance, a bass drum microphone does not need to reproduce high frequencies above 6 kHz or a vocal microphone may have a peak in the 2 – 4 kHz range to increase intelligibility.
Filters – Some studio condenser microphones feature a switchable high-pass filter, which can change the microphones frequency response to exclude frequencies below a certain point. This can be useful when recording instruments, such as acoustic guitar, when sub-bass frequencies may affect your headroom before distortion.
Depending on the instrument or the voice, different microphone options are available. Professional engineers will keep a wide variety of microphones available, and will experiment with different options to suit each application. However, when buying a large selection of microphones is not an option, there are a few guidelines to help you select the right microphone for you. No rules as such exist, but a good starting point would be to read our previous blog post “How to Choose the Right Mic”.
Join us for volume 4, where we will talk through the basics of microphone positioning. Subscribe to our RSS feed to be alerted. In the meantime, for more information on home recording products by Shure visit the home recording microphone page.