Richardson's handbook of projection (1930)

970 HANDBOOK OF PROJECTION FOR tance, hence it will be charging and discharging constantly as the diaphragm vibrates with the sound waves, and this charge and discharge will induce or set up in the circuit so attached a weak alternating current, which will have a frequency exactly equal to the frequency of the sound waves, and a strength exactly in proportion to the strength of the sound waves, which means in exact proportion to the acoustic energy of the source from which those sound waves originated. In other words we shall have an alternating current which is the exact replica, in electrical form, of the sound waves which formed it, assuming, of course, that the equipment is itself such as will give perfection in transposition from sound to electric, and that it be handled in a manner which will cause it to function perfectly. Because of the weakness of these electrical impulses, or as the engineers would say, because of the low energy level of this current, it is given one stage of amplification right at the microphone in order to prevent possible interference by stray currents on its way to the main amplifiers. The wires from the "mike" connect to the amplifying panel, where the current strength is amplified approximately one hundred million (100,000,000) times before being used to operate the recording apparatus. I believe you now have a fairly competent understanding of the means by which sound is made available, in the form of electric current, for the operation of the recording apparatus. This method does not vary, regardless of what recording method is employed. That is the story, then, of how the vibrating element of a human throat, called the "vocal cords," the vibrating