MORE THAN Sixty years ago, music was first transmitted and recorded. Within the last twenty of those years, both arts have received the serious attention of musicians, To meet their ideals the engineers have set themselves a high goal: that reproduction should be so faithful that one listening with his eyes closed would not know that the actual orchestra was not on the stage before him. Translated into physical requirements, such reproduction would comprehend the full tonal and volume ranges of the original, and in addition would have a spatial quality conveying a sense of width and depth.
To enjoy the full richness of music, one should hear far more than the tones which carry the melody, There are over-tones as well, and they extend several octaves above the highest note of any instrument. A practical limit is set by the range of the ear, which is from about thirty vibrations per second to about 15,000. A completely satisfactory electrical system must reproduce adequately at all vibration rates in this range.
In volume, as well, the ear has an effective range from sounds which are just audible to an acute ear, up to those which begin to be painful. Scientists have divided this range into 120 units, called "decibels." Below twenty decibels, casual noises in an auditorium will mask the music. Above 120 decibels, sound is too loud for comfort. Due to its mechanical limitations, an orchestra will leave unused a ten-decibel range inside each of these limits, but a conductor will frequently be glad to exercise electrical control on the sounds to make them even louder or softer than their originals.
The perception of the extent of the orchestra, and of the location of its several choirs and its soloists, which creates the final Illusion, requires that the reproduced sounds shall reach the audience from more than a single source. Ideally the entire width of a stage would be filled with sound-projectors, each of which would be energized independently by a microphone located in the same relative position in front of the orchestra. Practically, three such sound systems are adequate for a satisfactory illusion, and this is the arrangement in use tonight.