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CAPTURING AUDIO

Microphone Usage

 

Suggested Tasks for Study

 

1.  What is a transducer?

Sound is captured by a mic/transducer, converted to low electrical energy, amplified, then pushed out via another transducer/speaker to sound the same as the original. Thinking abstractly, where else in the world would you find something that completely changes form and then returns back to its original state?
Recording with a mic, storing the signal and then reproducing the sound through a speaker is just like___
 

 

 

 

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Post your idea in your portfolio.
 

2. Microphone Research 

Watch the following video on how mics work and take notes as needed.  

 

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KEY CONCEPTS

 

The Transducer
Impedance
Microphone Types

  • Dynamic

  • Condenser

  • Ribbon

  • PZM

  • Shotgun

  • Stereo Mics

Polar Patterns

  • Cardiod

  • Omni Direction

  • Bi-Directional

  • Hyper Cardiod

  • Shotgun

Cables

  • XLR

  • 1/4 inch

  • 1/8 inch

  • RCA

  • Impedance Converters

  • Speak-on Cables

  • Direct Box

Proximity Effect
Pad
Roll Off
Proper Usage of Microphones
Stereo Mic Techniques

RESEARCH TOOLS:

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Here is an old Powerpoint with some good information:


Using your best research techniques, gain a complete understanding of the following microphone types and characteristics:

  • Dynamic Mic

  • Condenser Mic

  • Ribbon Mic

  • PZM Mic

  • Shotgun Mic

  • Polar Patterns - which to use and when?

 

  • Electronic Pickups - Guitars and Basses

 

  • Proximity Effect - Explained below:  

 

 

 

Proximity effect in audio:
When a sound source is brought closer to a directional microphone, there is a change in the frequency response. The microphone's bass response increases significantly. A boost of 16 Db below 100 Hz is common. This can serve as a musical tool for vocalists who wish to "fatten up" their vocal timbre.

Notice the increased bass response as the sound source moves from one meter to 0.1 meter.

 

 

 

 

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PROXIMITY EFFECT ON DIRECTIONAL MIC:

Proximity Effect ExampleDirectional Mic
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Omni Directional microphones, ones that pick up sound data from all directions are less likely to exhibit the proximity effect. Omni mics do not rely on the differences in pressure in front and in back of the diaphragm. If you are interested why directional mics are affected by these pressures, read the excerpt below.

 

 

The movement of the diaphragm is a function of the air pressure difference across the diaphragm arising from incident sound waves. In a directional microphone, sound reflected from surfaces behind the diaphragm is permitted to be incident on the rear side of the diaphragm. Since the sound reaching the rear of the diaphragm travels slightly farther than the sound at the front, it is slightly out of phase. The greater this phase difference, the greater the pressure difference and the greater the diaphragm movement. As the sound source moves off of the diaphragm axis, this phase difference decreases due to decreasing path length difference. This is what gives a directional microphone its directionality.

The phase difference across the diaphragm gives rise to the pressure difference that moves the diaphragm. This phase difference increases with frequency as the difference in path length becomes a larger portion of the wavelength of the sound. (This frequency dependence is offset by damping the diaphragm 6 dB per octave to achieve a flat frequency response but this is not germane to the proximity effect so nothing more will be said about it here). The point to be made regarding the frequency dependency is that the phase difference across the diaphragm is the smallest at low frequencies. -http://wiki.myelectrical.com/index.php?title=Proximity_Effect

 

Prox EffectOmni Mic
00:00

 

3. KNOW YOUR CABLES

Audio Cables Usage Guide - Add Pics to your Portfolio, provide pics of Mics as well.

  • XLR Cable

  • RCA Cable

  • Optical Cable

  • TRS and Patch 1/4 inch and 1/8 inch Cable

  • Impedance Transformers

  • Speaker Cable

  • Speak-on Cables and adapters


 

 

 

 

 


4. Want to be the real deal?  Learn about Impedance  

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If you want the short answer, here it is: Low impedance is better than high impedance.
The letter Z is often used as shorthand for the word impedance

Any device which generates a voltage has what is called an output impedance
Any device which expects to receive a voltage input has an input impedance

High Impedance = More resistance
Low Impedance = Less resistance

Think of Electricity like water:

  • Water Pressure = In Electricity it is measured in Volts

  • Water Flow = In Electricity it is measured in Amps thought of as current

  • Pipe size or The Resistance of Flow = Impedance and is measured in Ohms.

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SM 58 Mic Technique!

The Objective is to "Match the Impedance"

The Small battery can only send a small amount of power (High Impedance). If you connected the small battery to the large light, the large light would need too much power, be dim, and kill the battery. It is like a Cow (the car light) is being fed a blade of grass instead of a pile of Hay... it will digest it immediately.

The Reverse
If you have a high impedance device receiving current from a Low Impedance power source, you are only using a fraction of the Low Impedance's capability and efficiency is lost. 
It is like buying 200 acres of land for your one cow to eat. You are not maximizing the potential of the land. The cow won't die but your land will be full of trees in no time.

A low impedance microphone should generally be connected to an input with the same or higher impedance. If a microphone is connected to an input with lower impedance, there will be a loss of signal strength. Think of trying to maintain the same amount of water flow when your hose suddenly has a bigger diameter.

 

 

In the Case of Speakers:


If you add an additional speaker "in series" you will reduce the resistance in the line. It is as if you had a bucket of water with a hole in it... add a speaker and add another hole.
In order to keep water in your bucket, you will need to increase the flow of water thus requiring more power. It requires more power to run additional speakers.


Check the Ohms rating on your amp and in your speakers.
 

 

What is Microphone Impedance?

All microphones have a specification referring to their impedance. This spec may be written on the mic itself (perhaps alongside the directional pattern), or you may need to consult the manual or manufacturer's website.
You will often find that mics with a hard-wired cable and 1/4" jack are high impedance, and mics with separate balanced audio cable and XLR connector are low impedance.


There are three general classifications for microphone impedance. Different manufacturers use slightly different guidelines but the classifications are roughly:

  1. Low Impedance (less than 600Ω)

  2. Medium Impedance (600Ω - 10,000Ω)

  3. High Impedance (greater than 10,000Ω)

Note that some microphones have the ability to select from different impedance ratings.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

METAPHOR

Think of this as having a nozzle at the end of a garden hose. The garden hose is a low impedance
source (there is little resistance to the flow of water) and the nozzle is the higher impedance of the
input being fed by the hose.


When the nozzle valve is closed (open circuit):
· Input impedance is VERY high
· Pressure (voltage) is at maximum
· Flow (current) is zero


Now open the nozzle just a little:
· Input impedance reduces but remains high
· Pressure reduces but remains high
· Flow is small
· You can hear lots of hiss from the spray (high frequencies)


As you continue to open up the nozzle:
· Input impedance reduces further
· Pressure reduces
· Flow increases
· Hiss from spray becomes less noticeable


With the nozzle open all the way:
· Input impedance is very low
· Pressure falls dramatically
· Flow is greatest
· 
Hiss from spray all but disappears
In the case of a high impedance guitar output (7,000 to 15,000 Ohms or more) driving a relatively
low impedance input of a mixer (2,000 to 10,000 Ohms), it's like connecting a garden hose to a
fire nozzle. The hose just can't produce enough flow (current) for the size of the opening to
maintain the pressure (voltage).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


5. Record using Stereo Mics:
Stereo mic technique will capture a decent left and right signal providing the recording a realistic sound of the acoustical space that you are using to record.  Each technique produces a significantly different result.


Stereo Mic Techniques:

  • XY Coincident Pairs

  • Stereosonic or Blumlein

  • M.S. (Mid-side)

  • Spaced Pairs- AB

  • Decca Tree

  • ORTF

  • Jecklin Disk

  • Binaural

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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Lost?  Not easy stuff.

AUDIO EXAMPLES OF THE FOLLOWING
TECHNIQUES:

 

 

Orchestra using Blumlein (Two bidirectional)
Orchestra using NOS (Spaced ORTF)
Trio Sonata AB
Trio Sonata NOS
Chamber Sonata MS
Chamber Sonata NOS

Blumlein
00:00
NOS
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Trio Sonata AB Mic
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Trio Sonata NOS
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Chamber Sonata MS
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Chamber Sonata NOS
00:00


EXPLORE THIS?
Set up the stereo mics in the music room. Create a sound to record, I.e., a musician. Test the XY, ORTF and MS techniques.
How can you compare the recordings?
Report your findings in your portfolio.

TIPS

  1. Speak or perform from various locations on stage to test stereo image--center, half-right, far right, half-left, far left. Announce your position.

  2. Playback the recording over speakers. Sit exactly between them, as far away from them as they are spaced apart.

 

 

 

 

 

 

 


4. Compare Mic types:

Here is the puzzle:
There are a variety of different microphone types. Each one picks up audio differently.

Find a way to compare and contrast microphones by recording audio in a manner that will measure the difference in the following:

  • Frequency range

  • Polar Patterns


Provide Screen Shots, Audio Files, written commentary to share your findings

Specifics:

      • Compare 2 different Dynamic Mics

      • Compare 2 different Condenser Mics (Record each polar pattern if applicable)

      • Compare Dynamic Mics to Condensor Mics

      • Test one of the Stereo Mics

      • Test polar patterns - back of a cardiod vs. front I.e., Cardioid pattern.mp3


Post all your finding on your portfolio

Take notes on Alan Parsons' video: Microphones
See instructor for Video


6 . Recording Project:

Consider working with a friend on this project.

Pick and instrument or voice part that you want to record. Research the best techniques for capturing the sound of the audio source.
Test at least two methods for recording the source.
Please make note of all equipment used during the session.
Compare your recordings as before and post your findings.

Pick your favorite and master it by adding the appropriate, compression, EQ and Reverb.

You can use this form to keep track of your work.
Recording Session Form.pages


Example:

  1. You are great cellist.

  2. Study how people have recorded your instrument

  3. Test out your findings.

  4. Make the exercise relevant.


Resources:
Mic the Guitar
Mic a Wind Instrument
Mic a Piano
Recording a Drum set
Mic a Voice project:
Other Recording Techniques Explored

Using portable recording devices: Dat decks

 

300px-XLR_pinouts.png

 

1
Chassis ground (cable shield)

2
positive polarity terminal ("hot")

3
return terminal[2] ("cold")

Review Here
TAKE THE MIC QUIZ HERE

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