Multiple time constant rectifier apparatus and method

A rectifier producing an output signal that is a function of the magnitude of an input signal with a controlled transient response, comprising:

• a capacitor;
• a charging current element coupled to said capacitor having a charging switch to regulate the flow of a charging current into said capacitor;
• a discharge current element coupled to said capacitor having a discharge switch to regulate the flow of a discharging current out of said capacitor;
• a switch controller which generates control signals for alternately turning on said charging switch and said discharge switch, said switch controller having an input signal terminal and an input corresponding to the voltage on said capacitor said switch controller including:
• a first comparator with a non inverting terminal coupled to said capacitor and its inverting terminal coupled to said input signal terminal;
• a first data flip-flop coupled to the output of said comparator;
• a voltage inverter;
• a second comparator with its non-inverting terminal coupled to said capacitor and its inverting terminal coupled to said input voltage terminal via said voltage inverter;
• a second data flip-flop coupled to the output of said comparator;
• and
• a logic gate connected to the outputs of said flip-flops to produce a logical output indicating whether the magnitude of the input voltage is greater than the voltage on said capacitor;
• and
• wherein said switch controller controls said switches so that a charging current increases the charge on said capacitor when the magnitude of the input signal is greater than the capacitor voltage and a discharge current decreases the charge on said capacitor when the magnitude of the input signal is less than the capacitor voltage.

A method of producing a rectified voltage of a signal with controlled attack and release response for an audio compressor, comprising the steps of:

• (a) providing a first rectification element, said first rectification element having a first output proportional to the magnitude of the input signal with a first preselected attack and release function;
• (b) providing a second rectification element, said second rectification element having a second output with a second preselected attack and release function, said first and second rectification element being emulated by a digital signal processor;
• and
• (c) summing said first and said second output.

A method of compressing an audio signal comprising the steps of:

• (a) detecting an input signal;
• (b) generating a first rectified signal which is a first function of the magnitude of said input signal and having a first preselected attack and release function;
• (c) generating a second rectified signal which is a second function of the magnitude of said input signal and having a second preselected attack and release function;
• and
• (d) summing said first and said second rectified signals for generating a combined signal having a third attack and release function.