Basic Audio ProductionA Quick Introduction to

Audio

What is “Audio?”

Audio means "of sound" or "of the reproduction of sound.”

Technical note: In physics, sound is a form of energy known as acoustical energy.

How Sound Waves Work

Sound waves exist as variations of pressure in a medium such as air.

How Sound Waves Work (cont.)

Sound waves are created by the vibration of an object, which causes the air surrounding it to vibrate.

How Sound Waves Work (cont.)

The vibrating air then causes the human eardrum to vibrate, which the brain interprets as sound.

How Sound Waves Travel

Sound waves travel through air in much the same way as water waves travel through water.

[The black dots represent air molecules.]

As the loudspeaker vibrates, it causes the surrounding molecules to vibrate in a particular pattern represented by the waveform.

The vibrating air then causes the listener's eardrum to vibrate in the same pattern. Voilà — Sound!

Note that air molecules do not actually travel from the loudspeaker to the ear (that would be wind). Each individual molecule only moves a small distance as it vibrates, but it causes the adjacent molecules to vibrate in a rippling effect all the way to the ear.

Variations in Air Pressure and Corresponding Waveform

Sound Wave PropertiesAll waves have certain properties. The three most important ones for audio work are:

Wavelength, Amplitude, Frequency

Wavelength

The distance between any point on a wave and the equivalent point on the next phase. Literally, the length of the wave.

Amplitude

The strength or power of a wave signal. The "height" of a wave when viewed as a graph.

Amplitude (cont.)

Higher amplitudes are interpreted as a higher volume, hence the name "amplifier" for a device which increases amplitude.

Frequency

The number of times the wavelength occurs in one second. Measured in kilohertz (Khz), or cycles per second. The faster the sound source vibrates, the higher the frequency.

Frequency

Higher frequencies are interpreted as a higher pitch. For example, when you sing in a high-pitched voice you are forcing your vocal chords to vibrate quickly.

Sound

All electronic audio systems are based around one very simple concept: To take sound waves, convert them into an electric current and manipulate them as desired, then convert them back into sound waves.

A very simple sound system

It is made up of two types of component:

Transducer

Amplifier

Transducer: A device which converts energy from one form into another. The two types of transducers we will deal with are microphones (which convert acoustical energy into electrical energy) and speakers (which convert electrical energy into acoustical energy).

Amplifier

Amplifier: A device which takes a signal and increases its power (i.e., it increases the amplitude).

1. The process begins with a sound source (such as a human voice), which creates waves of sound (acoustical energy).

2. These waves are detected by a transducer (microphone), which converts them to electrical energy.

3. The electrical signal from the microphone is very weak, and must be fed to an amplifier before anything serious can be done with it.

4. The loudspeaker converts the electrical signal back into sound waves, which are heard by human ears.

A slightly more elaborate system:

It still has Transducers and an Amplifier, but also has:

Signal Processors

Record and Playback

Signal Processors - devices and software which allow the manipulation of the signal

in various ways.

The most common processors are tonal adjusters such as bass and treble

controls.

Record and Playback - devices which convert a signal to a storage format for

later reproduction.

Recorders are available in many different forms, including magnetic tape, CD,

computer hard drive, etc.

1. The audio signal from the transducer (microphone) is passed through one or more processing units, which prepare it for recording (or directly for amplification).

2. The signal is fed to a recording device for storage.

3. The stored signal is played back and fed to more processors.

4. The signal is amplified and fed to a loudspeaker.

3-Part Audio Model

The Source is where the electronic audio signal is generated. This could be a "live" source such as a microphone or electric musical instrument, or a "playback" source such as a tape deck, CD, etc.

3-Part Audio Model

The Processing section is where the signal is manipulated. For our purposes, we will include the amplifiers in this section.

3-Part Audio Model

The Output section is where the signal is converted into sound waves (by loudspeakers), so that it can be heard by humans.

Microphones

Microphones convert acoustical energy (sound waves) into electrical energy (the audio signal).

Remember: Microphones are a type of transducer - a device which converts energy

from one form to another.

Microphones

Different types of microphone have different ways of converting energy but they all share one thing in common: the Diaphragm. This is a thin piece of material (such as paper, plastic or aluminium) which vibrates when it is struck by sound waves.

Microphones

When the Diaphragm vibrates, it causes other components in the microphone to vibrate. These vibrations are converted into an electrical current which becomes the audio signal.

Microphones

There are four basic types of microphones:

Dynamic

Ribbon

Condenser

Crystal

Dynamic Microphones

Are versatile and ideal for general-purpose use. They use a simple design with few moving parts. They are relatively sturdy and resilient to rough handling. They are also better suited to handling high volume levels, such as from certain musical instruments or amplifiers.

Dynamic Microphones

The Dynamic microphone uses a wire coil and magnet to create the audio signal

Condenser Microphones

A Condenser microphone has a diaphragm separated by carbon that acts as a capacitor. (A capacitor is a thing that stores electric energy.) The condenser microphone stores and releases the electronic signals when the diaphragm vibrates.

Condenser Microphones

They are capable of producing high quality sound and are used in the laboratory and studio recordings.

They are very sensitive and are used for voice. If you have a bad voice, don’t use a Condenser microphone, because they pickup sounds as they really are.

Ribbon Microphones

These microphones run with the help of a metal ribbon that is suspended in a magnetic field and is connected electrically to the microphone. This ribbon is moved by the sound waves that change the current flowing through it and thus electric signal is generated.

Ribbon Microphones

Ribbon microphones are very sensitive and usually used for special recordings. They are very fragile and can break easily.

Crystal Microphones

In these microphones, a crystal is attached to the diaphragm that creates the signal when the diaphragm gets vibrated by the sound waves. The crystals produce a voltage when subjected to pressure, to convert vibrations into electrical signals.

Crystal Microphones

Fairly durable and cheap. They are capable of producing high quality sound and are used in the laboratory and studio recordings.

They are likely used for capturing audio from a musical instrument.

Microphone Pickup Patterns

Every microphone has a property known as directionality.

This describes the microphone's sensitivity to sound from various directions.

Omnidirectional

Picks up sound evenly from all directions. (Omni means "all" or "every").

Omnidirectional

Capturing ambient noise; Situations where sound is coming from many directions; Situations where the mic position must remain fixed while the sound source is moving.

Unidirectional

Picks up sound predominantly from one direction.

This includes Cardioid and Hypercardioid microphones .

Unidirectional – Cardioid

Cardioid means "heart-shaped", which is the type of pick-up pattern this mic has. Sound is picked up mostly from the front, but to a lesser extent the sides as well.

The Cardioid is a very versatile microphone, ideal for general use. Handheld mics are usually cardioid.

Unidirectional - Hypercardioid

Very directional and eliminates most sound from the sides and rear. Due to the long thin design of Hypercardioids, they are often referred to as shotgun microphones

Bidirectional

Uses a figure-of-eight pattern and picks up sound equally from two opposite directions

Bidirectional

As you can imagine, there aren't a lot of situations which require this polar pattern. One possibility would be an interview with two people facing each other (with the mic between them).

Basic Audio ProductionA Quick Introduction to

Audio

Go make noise!