New "Camera" Photographs Sound in Four Seconds; Has an Increased Range

Sound can be photographed and scientifically analyzed in a few seconds by means of a new instrument built by Harry H. Hall, instructor in Physics at the Cruft Laboratory.

This machine is sensitive to sounds within the range of 50 to 10,000 vibrations per second, which is equivalent to about eight octaves. The most sensitive human ear can register sounds as low as 20 cycles and as high as 20,000 cycles, a range of about 10 octaves. The seven and one-half octaves, on a piano reach from 27 to 4176 cycles, while the greatest extent of human voice is 80 to 1950 cycles, or only about three and one-half octaves.

Higher-Than Piano

It is thus possible to analyses sounds of both higher and lower pitch than the human voice, as well as sounds more than an octave higher than the piano.

The instrument may be adjusted to complete the picture in 3.78 seconds, 6,61 seconds, or 10 seconds, Hall has spent over a year attempting to cut down on the several days require by older methods.

The apparatus picks up the noise to be analyzed through a microphone and passes it through an electric filter, cycles: the fundamental tone, the overtones, which produce the quality of sound, and the incidental sounds, such as the scratching of a violin bow.

This filter admits into the apparatus all parts of the noise from 50 to 10,000.

Only one pitch, however, is admitted at a time. The sounds of each frequency or pitch are admitted through the filter for a small fraction of a second and deflect a spot of light, generated by a cathodes ray tube, along a horizontal line in proportion to their strength. The sport, moving back and forth as higher and higher pitched sounds with different intensities are admitted, is photographed on sensitized paper and leaves a line graph. This graph is a picture record of the noise, showing the relative loudness of each of its component parts.

Permanent Value.

With a permanent record such as this the ecumenist is given time and material with which to study in detail the varying quality of voices and of musical instruments. Even though the sand note is played on two different instruments, its sound is noticeably different. This difference has been traced by previous experiments to the number, frequency, and strength of the ever tones.