Input Stage


Stage Purpose: 
picking up audio signals/waves and converting it to electrical signals by using some types of transducers.

Stage structure:
This stage consists of two main types of transducers or devices as follows:

- Microphones
- Sound recorders
 fig.1:Types of Microphones and Sound Recorders

Microphone:
It Converts the Audio Signals of the Speech to Electrical Signals (Direct Converters/transducers).

Types of Microphone:see fig.1

1-According to operation method:

A-Dynamic microphones
They are the most common and the most basic types of microphones. They consist of a diaphragm attached to a coil that moves through a magnetic Field inducing a small electrical signal. They operate using similar principals to a
Speaker and tend to have a limited frequency response, but are very rugged.

B-Condenser microphones
It has become more popular over the years because they have a very wide frequency response (tone) and are not as delicate or as expensive as ribbon microphones. They are, however, more delicate than dynamic microphones. They require a power source that can be an internal battery, an external power pack or phantom power that is provided by the mixer. They work by supplying a charge to a fixed plate that creates a capacitor. A thin diaphragm is mounted adjacent to the plate and induces voltage changes in the plate when subjected to sound vibrations.

C-Ribbon microphones
Produce sound by stretching a thin metal ribbon across a gap of a strong
Magnet. Sound moves the ribbon across the magnetic field creating electrical impulses. They have an excellent frequency response (tone) but tend to be very delicate and expensive. Since they are rarely used in basic P.A. systems, nothing more needs to be said about them.


fig.2: Polar Patterns

2-According to Polar Patterns: see fig. 2 

Polar patterns: This refers to the directions that the microphone will pickup sound from.
Polar patterns tend to be divided into two types:

- Omni 
- unidirectional.


1-Unidirectional Microphone:
Unidirectional Microphones are the most common and probably amount to more than 95% of all microphones sold. They range from shotgun (picking up sound from only straight in front of the microphone) to cardioids (picking up sound from in front of, or somewhat around the front of, the microphone in a heart shape pattern). Knowing the pattern of a microphone is important because it affects what area of sound that the microphone picks up from as well as its susceptibility to feedback.

2-Omni directional Microphone:
Are rarely used because they pick up sound from all directions and often pick up sound from directions you don’t want to have sound picked up from.

  
3- Special types of Microphones:

b-Lavalier microphone: is made for hands free operation but it was very small and it can be worn on the body fastened to clothes by clips and the cord is hidden by clothes which run to an RF transmitter.
Paging Microphone: used in paging system to announce messages Live or stored for broadcasting.

c-Chime Microphone: this type of microphone is equipped with chime function to announce before broadcasting the message.


Specifications of microphones:

1-Sensitivity:
This refers to the acuteness of “hearing” that a microphone possesses. the more Higher microphone sensitivity, the quieter sounds that it will pick up.

2- Impedance:
This is important to know so that you buy the proper microphone to match A Particular mixer. Although many mixers have inputs for both high and low impedance microphones, some only have one or the other. Generally speaking, if the microphone’s impedance is above 1,000 Ohms (1kOhm) it is considered high impedance, otherwise it is considered low. Most professional microphones are low impedance and come with a cable with XLR connectors. High impedance microphones generally come with a cable with phone (1/4”) connectors.

Sound Recorders:

Types of Sound Recorders:

A- Sound Tapes:
Magnetic tap recording involve the use of magentizable medium which moves with a constant speed past a recording head.
An electrical signal, which is analogous to the sound is to be recorded, is fed to the recording head including a pattern of magnetism similar to the signal. a playback head can then pick up the changes in magnetic field from the tape and convert into an electrical signal.

B- Sound CDs:
Sound CDs is a pre-pressed compact disc that contains data accessible to, but not written by, a computer for data storage and music playback.
Sound CDs have many types ,formats and sizes but all needs CDs driver or DVDs Drivers for operation.


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