After Alexander Graham Bell invented the telephone, and telephone lines began to be stung up all over, the Bel, spelled B-e-l, was the loss of signal strength in one mile of telephone line. A decibel then, is one tenth of microphone output is generally in the range of -65 to -85 level, the signal level that audio devices operate is typically +4 dB for professional gear, like recording consoles, digital audio workstations, tape recorders, and outboard signal processors. For consumer gear like TVs, CD and DVD players. the line level is -10 dB, 14 dB lower. Generally any analog input or output that uses an RCA or phono connector is at the -10 dB a 14 difference between professional and consumer line level may not seem like that much, remember that an increase of only 6dB doubles the volume.