How to Convert Raw G.711 μ-law and A-law Audio to WAV in Your Browser

If you work with PBX phone systems, VoIP servers (such as Asterisk, FreePBX, or 3CX), call center compliance archives, or legacy IVR voice prompts, you have almost certainly encountered .ulaw, .alaw, or .pcm audio files.

When you double-click these files on a modern Windows, Mac, iOS, or Android device, the operating system usually throws an error: "Unsupported file format". Standard media players cannot open them because raw G.711 files lack container headers (such as RIFF chunks or sample rate declarations).

This guide covers the engineering behind ITU-T G.711 companding, why telephony systems store headerless audio, and how to convert raw G.711 bitstreams to playable 16-bit linear PCM WAV files in your browser using convrtr's G.711 to WAV converter.

What is ITU-T G.711?

Standardized in 1972 by the International Telecommunication Union, G.711 is the foundational codec of the digital telephone network (PSTN) and Integrated Services Digital Network (ISDN).

G.711 samples human speech at 8,000 Hz (8 kHz). However, rather than encoding linear 16-bit amplitude values (which would demand 128 kbps of bandwidth per channel), G.711 employs companding (compressing and expanding) to quantize speech into 8-bit bytes, cutting bandwidth to exactly 64 kbps.

μ-law vs A-law Companding

There are two primary variants of G.711:

1. μ-law (PCMU / Mu-Law): Primarily used in North America (USA, Canada) and Japan. It uses a logarithmic curve defined by parameter μ = 255, offering slightly better dynamic range for quiet speech.
2. A-law (PCMA): Used throughout Europe and the rest of the world. It employs a piece-wise linear approximation of logarithmic companding (A = 87.6).

Both algorithms achieve approximately 12 to 14 bits of perceptual dynamic range within an 8-bit byte by allocating finer quantization steps to quiet sounds (where the human ear is sensitive to distortion) and coarser steps to loud sounds.

The Headerless Challenge

When audio is packaged in a WAV container, it includes a 44-byte RIFF header detailing:

• Number of channels (mono/stereo)
• Sampling rate (e.g., 8,000 Hz, 44,100 Hz)
• Bits per sample (e.g., 8-bit, 16-bit)
• Byte rate and block alignment

In contrast, raw .ulaw and .alaw files contain zero header bytes—only continuous streams of 8-bit sample bytes. Without an explicit header, standard media players have no way of knowing whether the file represents 8 kHz voice telephony, 44.1 kHz music, stereo, or mono.

Converting G.711 to Standard WAV

To make these recordings audible on consumer devices, each 8-bit companded byte must be mathematically decompanded into a 16-bit signed integer (-32,768 to 32,767) and wrapped in a valid RIFF/WAVE header.

convrtr's G.711 to WAV converter performs this process seamlessly in your browser:

1. Direct Byte Decompanding: Uses lookup tables and bit-shift expansion for instant, zero-latency sample decoding.
2. Custom Sample Rate Support: Defaults to the standard 8,000 Hz telephony rate while offering options for 16,000 Hz, 11,025 Hz, or custom rates.
3. Codec Selection: Effortlessly switches between μ-law and A-law decoding tables.
4. Header Construction: Assembles a byte-perfect 16-bit mono RIFF WAV header with exact block alignments.

Because the conversion runs 100% locally in WebAssembly and JavaScript, confidential customer calls, legal depositions, and private voicemail archives remain strictly confidential on your machine.