pcm - Python u-Law (MULAW) wave decompression to raw wave signal

Pcm - Python u-Law (MULAW) wave decompression to raw wave signal

To decompress a u-Law encoded PCM audio file (often used in telephony and VoIP applications) into a raw wave signal (PCM), you can follow these steps using Python. The u-Law algorithm is typically used for compressing dynamic range audio data into a smaller range suitable for transmission over telecommunication lines. Here's how you can decompress it to obtain the raw wave signal:

Steps to Decompress u-Law Encoded PCM

  1. Read the u-Law Encoded PCM File: Read the binary data from the u-Law encoded PCM file.

  2. Decode u-Law to PCM: Convert the u-Law encoded data to PCM format using the appropriate formula.

  3. Write the PCM Data to a WAV File: Save the decoded PCM data as a WAV file, which is a standard format for raw audio data.

Example Python Code

Here's an example Python code snippet that demonstrates how to decode u-Law encoded PCM data:

import wave import numpy as np def decode_ulaw(data): """Decode u-law encoded data to PCM""" max_value = 32767.0 # 2^15 - 1 u_law_max = 255.0 data = np.array(data, dtype=np.uint8) data = data.astype(np.int16) sign = data & 0x80 exponent = (data & 0x70) >> 4 mantissa = data & 0x0F mantissa = mantissa / u_law_max exponent = (exponent + 1) * 2 pcm = (1 - sign) * (mantissa * (2 ** exponent) - (2 ** (exponent - 1))) return pcm.astype(np.int16) def ulaw_to_pcm(input_ulaw_file, output_pcm_file): """Convert u-law encoded WAV file to PCM WAV file""" with wave.open(input_ulaw_file, 'rb') as ulaw_file: params = ulaw_file.getparams() ulaw_data = ulaw_file.readframes(params.nframes) pcm_data = decode_ulaw(ulaw_data) with wave.open(output_pcm_file, 'wb') as pcm_file: pcm_file.setparams((params.nchannels, params.sampwidth, params.framerate, params.nframes, params.comptype, params.compname)) pcm_file.writeframes(pcm_data.tobytes()) # Example usage ulaw_file = 'input_ulaw.wav' pcm_file = 'output_pcm.wav' ulaw_to_pcm(ulaw_file, pcm_file) print(f"Successfully converted {ulaw_file} to {pcm_file}")

Explanation:

  1. decode_ulaw Function:

    • decode_ulaw decodes u-law encoded data to PCM using the formula specific to u-law decoding. This function applies the u-law decoding algorithm to each byte of the input data.

  2. ulaw_to_pcm Function:

    • ulaw_to_pcm function reads the u-law encoded WAV file (input_ulaw_file), decodes the u-law data using decode_ulaw, and writes the resulting PCM data to a new WAV file (output_pcm_file). It uses Python's wave module to handle WAV file reading and writing.

  3. Example Usage:

    • Replace 'input_ulaw.wav' with the path to your u-law encoded WAV file.
    • Replace 'output_pcm.wav' with the desired path for the output PCM WAV file.

Notes:

  • Data Type Conversion: The example assumes 16-bit signed PCM data (np.int16). Adjust the data type according to your specific requirements if different.

  • Endianness: Ensure that the endianness of your system matches the WAV file format. This example assumes little-endian format, which is common on most systems.

  • Wave Module: The wave module in Python provides convenient methods for reading and writing WAV files, handling parameters like number of channels, sample width, and sample rate.

Examples

  1. How to decode u-Law encoded PCM audio to raw wave signal using Python? Description: Implementing the u-Law decoding algorithm in Python to convert MULAW encoded PCM waves to raw wave signals.

    import numpy as np def decode_mulaw(data, channels=1): max_value = 32768.0 data = np.array(data, dtype=np.int16) sign = data & 0x8000 exponent = (data >> 8) & 0x7F mantissa = data & 0xFF decoded = np.where(data >= 0x8000, -(1 << exponent) + (mantissa << (exponent - 7)), ((data & 0x7FFF) << 4) + 8) return decoded / max_value # Usage example mulaw_data = ... # Replace with your u-Law encoded PCM data raw_wave = decode_mulaw(mulaw_data)

  2. Python implementation to convert u-Law encoded audio to PCM wave format? Description: Converting u-Law encoded audio data into PCM wave format using Python.

    import numpy as np def decode_mulaw(data): mulaw_table = np.array([((i << 1) + 1) / 65536.0 for i in range(256)]) decoded = np.sign(data) * (1.0 / 255.0) * ((1.0 + mulaw_table[np.abs(data)]) ** 255.0 - 1.0) return decoded # Usage example mulaw_data = ... # Replace with your u-Law encoded PCM data pcm_wave = decode_mulaw(mulaw_data)

  3. How to decode u-Law encoded audio files in Python using scipy? Description: Using scipy to decode u-Law encoded audio files into raw wave signals.

    import scipy.io.wavfile as wavfile def decode_mulaw(data): return np.sign(data) * (1.0 / 255.0) * ((1.0 + np.power(255.0, np.abs(data)) - 1.0)) # Usage example mulaw_data = ... # Replace with your u-Law encoded PCM data raw_wave = decode_mulaw(mulaw_data)

  4. Python code to convert u-Law encoded audio to linear PCM? Description: Writing Python code to convert u-Law encoded audio data to linear PCM format.

    def mulaw_decode(x): mu = 255 max_value = 32768.0 x = x - max_value sign = np.sign(x) x = np.abs(x) x = (1 / mu) * ((1 + mu) ** x - 1) * sign return x # Usage example mulaw_data = ... # Replace with your u-Law encoded PCM data linear_pcm = mulaw_decode(mulaw_data)

  5. How to decode u-Law audio using NumPy and Python? Description: Utilizing NumPy in Python to decode u-Law encoded audio into raw wave signals.

    import numpy as np def decode_mulaw(data): mu = 255 return np.sign(data) * (1.0 / mu) * ((1.0 + mu) ** np.abs(data) - 1.0) # Usage example mulaw_data = ... # Replace with your u-Law encoded PCM data raw_wave = decode_mulaw(mulaw_data)

  6. Python script to convert u-Law encoded audio to raw PCM wave data? Description: Writing a Python script to convert u-Law encoded audio data to raw PCM wave format.

    def decode_mulaw(data): max_value = 32768.0 return np.sign(data) * (1.0 / 255.0) * ((1.0 + np.power(255.0, np.abs(data)) - 1.0)) # Usage example mulaw_data = ... # Replace with your u-Law encoded PCM data raw_wave = decode_mulaw(mulaw_data)

  7. How to decode u-Law encoded audio to PCM using Python's wave module? Description: Using Python's wave module to decode u-Law encoded audio data into PCM wave format.

    import wave def decode_mulaw(data): max_value = 32768.0 return np.sign(data) * (1.0 / 255.0) * ((1.0 + np.power(255.0, np.abs(data)) - 1.0)) # Usage example mulaw_data = ... # Replace with your u-Law encoded PCM data raw_wave = decode_mulaw(mulaw_data)

  8. Python code snippet to convert u-Law audio to raw PCM audio data? Description: Providing a Python code snippet for converting u-Law audio data to raw PCM audio format.

    def mulaw_decode(x): mu = 255 max_value = 32768.0 x = x - max_value sign = np.sign(x) x = np.abs(x) x = (1 / mu) * ((1 + mu) ** x - 1) * sign return x # Usage example mulaw_data = ... # Replace with your u-Law encoded PCM data raw_wave = mulaw_decode(mulaw_data)

  9. How to implement u-Law decoding in Python for audio processing? Description: Implementing u-Law decoding functionality in Python for processing audio data.

    def decode_mulaw(data): max_value = 32768.0 return np.sign(data) * (1.0 / 255.0) * ((1.0 + np.power(255.0, np.abs(data)) - 1.0)) # Usage example mulaw_data = ... # Replace with your u-Law encoded PCM data raw_wave = decode_mulaw(mulaw_data)

  10. Python function to convert u-Law encoded PCM audio to raw wave signal? Description: Creating a Python function to convert u-Law encoded PCM audio data to raw wave signal.

    def decode_mulaw(data): max_value = 32768.0 return np.sign(data) * (1.0 / 255.0) * ((1.0 + np.power(255.0, np.abs(data)) - 1.0)) # Usage example mulaw_data = ... # Replace with your u-Law encoded PCM data raw_wave = decode_mulaw(mulaw_data)

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