The mel scale is a scale set up in an effort to quantify and measure the psychoacoustic phenomenon of pitch. It was originally developed in 1937 by Stevens, Volkmann, and Newmann, and consists of a scale of pitches judged by listeners to be equal in distance one from another. The reference point between this scale and normal frequency measurement is defined by equating a 1,000 Hz tone, 40 dB above the listener's threshold, with a pitch of 1,000 mels. Below about 500 Hz the mel and hertz scales coincide; above that, larger and larger intervals are judged by listeners to produce equal pitch increments. Consequently, four octaves on the hertz scale above 500 Hz are judged to comprise about two octaves on the mel scale.