Threshold - The slider attached to the input meter on the left is the Threshold control. The Threshold sets the input signal level where the overall compression begins to take effect. The Threshold can be set anywhere between -60 and 0 dB.
Frequency Range - The Frequency Range section allows you to select the specific frequency range that gets processed by the compressor. The 18 compressor bands will be distributed across whatever range is selected. For example, with Mid selected, all 18 bands will be focused on the Mid range, allowing for more precise control over the frequencies within that range.
The available Frequency Range options are as follows: Full Range, 16 Hz - 20 kHz, High, 3 kHz - 20 kHz, High Mid, 200 Hz - 18 kHz, Mid, 180 Hz - 7 kHz, Low Mid, 12 Hz - 8 kHz, Low, 15 Hz - 500 Hz