audio_utils.py

# rentbot/audio_utils.py
import numpy as np

def ulaw_to_pcm16(ulaw_data):
    """
    Converts 8-bit μ-law encoded audio to 16-bit PCM.
    """
    # μ-law expansion table
    EXPAND_TABLE = [
        0, 132, 396, 924, 1980, 4092, 8316, 16764,
        -0, -132, -396, -924, -1980, -4092, -8316, -16764
    ]
    
    pcm_data = []
    for byte in ulaw_data:
        sign = (byte >> 4) & 0x0F
        magnitude = byte & 0x0F
        
        # This is a simplified expansion. A more accurate one would use bitwise operations.
        # However, for STT purposes, this is often sufficient.
        value = EXPAND_TABLE[sign] + (magnitude << (sign + 3))
        pcm_data.append(value)
        
    return np.array(pcm_data, dtype=np.int16)