Designing an audio compressor circuit involves several components and considerations to achieve dynamic range control. Here's a simplified step-by-step guide to designing a basic audio compressor circuit:
Voltage-Controlled Amplifier (VCA): The heart of the compressor that adjusts the gain based on the input signal's level.
Detector Circuit: Measures the input signal's level and generates a control voltage for the VCA.
Control Voltage Source: Provides the threshold and ratio control voltages for the detector.
Make-up Gain Amplifier: Adds gain to the compressed signal to restore lost loudness.
Input and Output Stages: Buffer the input and output signals to prevent loading issues.
Use a simple rectifier circuit (diode followed by a capacitor) to convert the AC audio signal into a varying DC voltage proportional to the signal's amplitude.
The capacitor smooths out the rectified waveform to create an envelope that follows the input signal's amplitude variations.
Control Voltage Source:
Determine the desired threshold and ratio values for compression. These values will determine when and how the compressor starts to reduce gain.
Design a voltage divider network using resistors to generate the threshold voltage. This voltage sets the level at which compression begins.
Similarly, design another voltage divider network for the ratio control voltage. This voltage sets the amount of gain reduction applied beyond the threshold.
Voltage-Controlled Amplifier (VCA):
Choose an operational amplifier (Op-Amp) based VCA design. An Op-Amp can be used in an inverting amplifier configuration.
The control voltage from the detector circuit is connected to the inverting input of the Op-Amp. The input audio signal is connected to the non-inverting input.
The Op-Amp amplifies the difference between the input audio signal and the control voltage, effectively controlling the gain based on the input signal's level.
Make-up Gain Amplifier:
Use another Op-Amp-based amplifier circuit to add gain to the compressed signal.
The gain can be set manually or controlled using a potentiometer.
Input and Output Stages:
To avoid loading issues and maintain impedance matching, add buffer stages at the input and output of the compressor circuit.
Each buffer stage can be designed using an Op-Amp in a unity gain configuration.
Remember that this is a simplified explanation, and there are many variations and optimizations you can implement in a real-world audio compressor circuit. The component values, amplifier gains, and other parameters will depend on your specific requirements and the components you're using. Additionally, considering factors like attack and release times, noise performance, and distortion can lead to more complex designs. Always simulate and test your circuit to ensure it meets your desired compression characteristics.