Frequency response of the Passive insertable tone control circuit. The vertical axis is marked off in dB from minus 40 to 0. The horizontal axis is a logarithmic scale that runs from 10 Hz to 100 kHz.

The tone flat line is red and begins at 10 Hz and -20 dB. As it runs to the right it falls slightly coming down to about -21 dB at 500 hz. After that it rises a little going across the rest of the graph but never gets back to -20 dB.

The full cut line is green and starts out at -40 dB. It rises crossing -36 dB at 70 Hz, -32 dB at 120 Hz, -28 dB at 210 Hz, -24 dB at 400 Hz, crosses the tone flat line at 700 Hz, rises to a maximum at -20 dB at 1200 Hz, begins descending, crosses the tone flat line again at 1800 Hz, passes -24 dB at 3500 Hz, -28 dB at 6500 Hz, -32 dB at 13 kHz, then levels out at -35 dB from 35 kHz to 100 kHz.

The half cut line is blue and should be half way between flat and full cut, but it isn't. It begins at 10 Hz and just a little below the -28 dB line, it crosses the -28 dB line at 25 Hz and continues to rise, it rises above the tone flat line at 280 Hz, it reaches a maximum at 600 Hz and just above the -20 dB line, as it falls it crosses the green line which it is never supposed to do and remains about a dB below it until it crosses again at 3000 Hz, it crosses -24 dB at 4300 Hz, it levels out at 10 kHz and -26 dB continuing on to 100 kHz.

The full boost line is purple and begins at 10 Hz and -1 dB, it falls to -4 dB at 80 Hz, -8 at 150 Hz, -12 at 260 Hz, -16 at 4400 Hz, It crosses the blue line at 800 Hz, the green line at 900 Hz, crosses back over the blue line at 1100 Hz and the green line at 1200 Hz, its minimum value occurs at 1000 Hz, it rises crossing -16 dB at 2300 Hz, then crosses -12 at 4000, -8 at 9000, and leveling off at -6 dB at 20 kHz and continuing on to 100 kHz.

The half boost line is light blue and begins at 10 Hz and -11 dB, it crosses -12 dB at 22 Hz, -16 at 60, crosses -20 at 150, the red line at 190, the blue line at 230, touches the green line at 600, and remains in contact with it until 1100 Hz, meanwhile crossing the purple line at 900 Hz, it crosses the purple line again at 1080, then levels off at -16 dB and 10 kHz. It continues flat out to 100 kHz.

In the area around 1000 Hz the lines are a tangled mess. They should never cross. The half cut line should always remain between the full cut line and tone flat. The half boost line should always remain between the full boost line and tone flat.

End verbal description.
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