Recording of Sound

Recording of Sound 

The recording of sound is done on a flat circular disc/slab which is 1.5 inches thick and about 12 inches in diameter . The track of this disc is a wavy groove of uniform depth . This disc is made up of special wax and a highly polished plane surface and rotated at a constant speed at the time of recording of sound.

Construction of the mechanical arrangement to record sound : 

According to the diagram shown above , a shaft carrying the cutting stylus is attached to a soft iron armature , situated between the two poles of an electromagnet . A recording needle is fixed in the armature and tipped with sapphire which traces out the desired spiral groove on the surface of wax slab which is rotating at a constant speed under the cutter .

Working :- The stylus or the recording part cuts lateral groove along the circumference of the disc and also moves radially along the disc .

The sound which is to be recorded is collected by a microphone . Microphone converts the sound waves into electrical waves or fluctuations which are later amplified with the help of an amplifier . When the amplified sound or speech passes from the fixed coils in the form of current  , then the intensity of the magnetic field changes . This variation is of magnetization in the armature provide it a vibratory motion . The recording needle traces out the desired spiral groove on the surface of wax slab which is rotating at a constant speed under the cutter .

Now , this circular disc is dusted by fine bronze powder and then electroplated until a thin layer of copper is deposited on the surface of this disc . Thus thin copper plate is referred as Master or Negative .

After this all happened , the negative is carefully stripped off the wax disc . This negative contains the impressions of sound waves from the wax in the form of ridges in place of simple grooves .

A further dwpost of copper is made on the side of the negative and again peeled off provides it a working positive which is of no use .

By repeating this process , another negative of it can be prepared , which after suitable mounting is used for making impression on the shellac disc , which forms the final record .

•The material used for record is a mixture of shellac , resin and a number of other constituents .

•The impression is made under pressure on the disc and disc is slightly softened by heat .

This was a knowledge about process of recording of sound . 

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