simple_compressor.py

import numpy as np


class SimpleCompressor:
    """
    Simple dynamic range compressor using logarithmic waveshaping.
    
    Compresses audio toward +/-1 on a logarithmic scale, making quiet sounds
    louder while keeping peaks under control.
    """
    
    def __init__(self, strength: float = 1.0, sample_rate: int = 44100):
        """
        Initialize compressor.
        
        Args:
            strength: 0.0 = none; value can be greater than 1.0
            sample_rate: Audio sample rate (unused but kept for API compatibility)
        """
        self.strength = strength
        self._sample_rate = sample_rate
    
    def set_sample_rate(self, sample_rate: int) -> None:
        """Update sample rate (for API compatibility)."""
        self._sample_rate = sample_rate
    
    def reset(self) -> None:
        """Reset compressor state (no state to reset for waveshaper)."""
        pass
    
    def process(self, audio: np.ndarray, strength: float | None = None) -> np.ndarray:
        """
        Process audio through logarithmic compressor.
        
        Uses the formula: out = sign(in) * (1 - (1 - |in|)^((1-strength)*2 + 0.5))
        - strength=0: exponent=0.5 (sqrt, mild expansion)
        - strength=0.5: exponent=1 (linear, no change)
        - strength=1: exponent=2.5 (strong compression toward +/-1)
        
        Args:
            audio: Input audio array (n_samples, n_channels)
            strength: Override strength value; uses self.strength if None
            
        Returns:
            Compressed audio array
        """
        audio = audio.copy()
        
        # Use provided strength or fall back to instance strength
        effective_strength = strength if strength is not None else self.strength
        
        # Calculate exponent from strength (0.5 to 2.5)
        exponent = (1 - effective_strength) * 2 + 0.5
        
        # Get absolute values
        abs_audio = np.abs(audio)
        
        # Avoid log(0) by clipping to small value
        abs_audio = np.clip(abs_audio, 1e-10, None)
        
        # Logarithmic compression: compress toward 1
        # Formula: out = sign(in) * (1 - (1 - |in|)^exponent)
        # This pushes values toward +/-1
        compressed = 1 - np.power(1 - abs_audio, exponent)
        
        # Restore sign
        audio = np.sign(audio) * compressed
        
        return audio