The arithmetic difference between the cut-off frequencies or – 3 dB points in a response curve, expressed in octaves or as a frequency difference in Hertz.
"The product arrived in fine shape - thank you so much for restoring the tape - I was surprised it came out as well as it did. The voice was my grandfather's from 48 years ago, 1962. He is long gone now but I remember the Christmas gathering rather well. Many memories came back in a rush."