Impmooc – Week 1 – Microphones

Hi there! My name is Karyn Ellis. I am a professional songwriter / performer from Toronto, Canada.

Today I am going to talk about microphones. In the following lesson, I will cover how the choice of microphone type, frequency response and polar pattern impacts the qualities of the sound signal created by a microphone.

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What a Microphone Does

A microphone is a TRANSDUCER. A transducer converts one energy type into another without (significantly) changing the quality of the sound signal. When you sing or play into a microphone, the sound pressure variations created in the air by your voice or instrument enter the microphone and are converted into voltage variations. These voltage variations are then transmitted via wire out from the microphone to the next stage in the signal flow –> the mic pre-amp.

There are several ways the signal is converted; it depends on the type of microphone and its inner electronics. Without getting into technical details, we can say the real world imposes its physical properties on how a microphone treats sound — each way has *some* effect on colouring the sound. We may try to record as accurate a representation as possible, and we can also intentionally choose to affect the signal, for example, by selecting a microphone that favours frequencies of the instrument we are recording.


Types of Microphones

There are two main types of microphones used in the studio: DYNAMIC and CONDENSER.

A. DYNAMIC
The SM58 is a popular dynamic mic.

  • They are rugged, resistant to moisture and rough handling.
  • They most often have a directional polarity pattern (we’ll talk about polar patterns more later on), and that makes these mics especially suitable for vocals in a live performance situation. They are designed to pick up sound in front of them and reject sound from behind, which means on-stage monitors generally won’t cause feedback.
  • They are not particularly sensitive to input, which also makes them well suited in the studio for high volume levels such as close-proximity miking of drums and amps.
  • They will colour the sound signal as it is converted. Because of the physics of how a dynamic microphone works, they usually have an upper frequency-response limit of around 16kHz, as opposed to the 20kHz of a good condenser mic*. They can sound less “sparkly” than a condenser mic. Sometimes this can be a production choice in the studio, eg capturing a rock vocals sound. *Source: http://www.soundonsound.com/sos/apr98/articles/mic_types.html

B. CONDENSER
The AKG 414 is a popular condenser mic.

  • They are sensitive to sound input. They can transmit quiet and distant sounds quite well, as well as respond to the low-energy sound waves of the lowest and highest frequencies ranges.
  • Usually condenser mics are designed to have a flat frequency response that won’t colour the sound much. They are considered to be “transparent” and create an accurate representation of the original sound. Because they offer “what you hear is what you get”, they are frequently used in the studio.
  • They are not very robust and are susceptible to damage from rough handling and condensation.
  • Their sensitivity to input (high potential for feedback) and their fragility make them less suitable for the conditions of live shows. Occasionally they are used for drum overheads in the live setting, but with care not to route the signal back into the monitors to avoid feedback.
  • The electronics in the microphone require phantom power +48V in order to work.

Microphone Response

Microphones are designed for a variety of specific uses. For example, the SM58 is designed for vocals – it tends to reject frequencies outside of the human vocal range. On the other hand, the AKG 414 has a more even frequency response designed to pick up everything as accurately as possible, with as little colouration of the sound as possible.

Every microphone has its own FREQUENCY RESPONSE CHART. This indicates what that microphone picks up well and what frequencies it will reject, essentially acting as an initial EQ filter. If you want to be particular, there are mics specifically designed for saxophones, guitars, chamber instruments, vocal ranges etc.

Comparing the two standard mics – SM58 (dynamic) and AKG 4141 (condenser), here are two contrasting specs:

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SM58 [Dynamic. 5000 Hz peak, amplifies vocal range. Rolls off high and lows.]

SM58freqresponse600x340px

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AKG 414 [Condenser. Considered a flat frequency response. Designed to pick up everything as accurately as possible with minimal EQ effect.]

AKG414freqresponse600x340px


Microphone Polar Patterns

In addition to type and frequency response, a microphone is also designed to accept and reject sound that arrives from different directions. This is called its POLAR PATTERN. There are three main patterns:

A. UNIDIRECTIONAL

This is also known as a CARDIOID microphone – dynamic mics often have this polar pattern, but it can also be a setting on a multi-setting condenser mic. It isolates sound by picking up what is directly in front of the mic and rejecting sound from its back end. This gives a focused sound with very little room (limiting the reflections that define the shape and size of the space.)

cardiod200px

    Variations of the unidirectional pattern include:

  • SUPER CARDIOID: This is slightly more focused than the regular cardioid.
    supercardiod200px
  • HYPER CARDIOID: This microphone accepts sound from the front of the mic, and to a lesser extent from the back. Less from the sides than the cardioid or supercardioid.
    hypercardiod200px

Unidirectional microphones are subject to the PROXIMITY EFFECT: this is where bass response is significantly boosted (“boomy”) when the sound source is at close distances to the mic.

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B. OMNIDIRECTIONAL

This microphone accepts sound from all directions. This gives lots of “room” to the sound and is useful for picking up ambient sounds, large groups, or when the sound source is moving around.

omnidirectional200px

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C. BIDIRECTIONAL

Also known as FIGURE-8, this microphone accepts sound from front and back of the microphone, but not the sides. It can be used in stereo recording and also when simultaneously recording two instruments / 2-person interviews.

figure8-200px


Considerations When Choosing a Microphone

As you can see there are a number of factors to consider when choosing a microphone. To help decide which mic will work best for a particular application, here are some questions to ask yourself.

Do you want to capture the sound of the space where you are recording, or do you want to isolate the instrument? (Polar pattern – directionality; type of mic – sensitivity of mic to sound input.)

How much do you want the mic to colour the sound? (Type of mic; frequency response; polar pattern – the proximity effect.)

How loud is the sound you are recording? (Type of mic – sensitivity of mic to sound input.)

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REFLECTION on the PROCESS:

Thank so much for taking the time to read and critique my lesson. Any feedback you have would be great.

I enjoyed working on this assignment – so much so that I probably put in waaaay too many hours doing it. I had some neat a-ha moments going through the material. Like, wow… those polarity patterns & frequency response charts make way more sense to me now! It was challenging to bring the topic down to a thousand words (and to be honest, I think I went over by about seventy-five) because there is so much more I could say about it. Didn’t even get to ribbon mics and PZMs! :) Who knew mics could be so interesting.

I think I’ve got the dynamic / unidirectional thing straight in my mind, but if you have any further insights about how they are and are not related please let me know.

I’m also curious whether this succeeded as a “lesson” in its written format or whether it seems to be more of an article. Also, I wonder how readable it is – whether there is enough formatting and images.

PS, I decided to go with the written form rather than a video lesson because I am away from home at the moment and didn’t feel comfortable setting up a shoot while I’m a guest in someone else’s house.

Thanks again! Hope you enjoyed & learned something!
Best, Karyn

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