SCIENCE STUDIES THE NEGRO SPIRITUAL FACIAL EXPRESSION
Legend - Another film record of a singer's voice.
The longer waves are made by the tuning fork, vibrating a hundred times a second, so that the waves of the irregular voice record between the same part of two successive waves of the fork, as between C and D, show what happened in a hundredth of a second.
This was a more complicated sound than the voice wave in the other
record, which showed almost a pure note.