A compressor expander based on the design of a compander chip designed for telephone lines and used in many electronic devices to reduce the noise.
The chip works with a fixed threshold (in our case is internally set to -18dBFS) when the “amount” knob is at a value greater than 1 the gain is increased by the specified factor if the signal is below the threshold, and decreased if above. If the chip is set to work as an expander, the contrary happens, the gain is increased if above the threshold and decreased if below.
The system is designed this way to permit dynamic compression on telephone lines and compressor and expander are used together in this configuration, but we found that these models sounds interesting by themselves.
The model of this chip is implemented in the HoRNet HDD1 where is used to keep the noise down in the delay feedback loop.
Internally the gain is compensated so that the output is always kept to around -18dB RMS