Converting Westwood Studios AUD Audio (.AUD) to Linear PCM WAV

In the golden age of real-time strategy (RTS) gaming, few sound effects and voice lines are as indelible as "Unit ready," "Affirmative," and "Construction complete" from Westwood Studios' legendary titles: Command & Conquer (1995), Command & Conquer: Red Alert (1996), and Dune 2000 (1998).

To compress hundreds of distinct unit responses, explosion sounds, and Frank Klepacki's driving industrial rock soundtracks onto 650 MB CD-ROMs, Westwood audio engineers designed their own compact audio container: the .aud file.

Because modern media players, DAWs, and game engines cannot decode Westwood's ADPCM chunk streams natively, game modders, audio archivists, and retro enthusiasts need a reliable way to convert .aud files to standard 16-bit linear PCM WAV.

This guide explores the structure of the 12-byte Westwood AUD header, the mechanics of WS-ADPCM and IMA-ADPCM, and how to convert .aud files directly in your browser with convrtr's Westwood AUD to WAV converter.

Anatomy of the 12-Byte Westwood AUD Header

Every Westwood .aud audio file begins with a compact 12-byte binary header:

Offset  Length  Type     Description
-------------------------------------------------------------
0x00    2       uint16   Sample Rate (e.g. 22050, 11025, 44100 Hz)
0x02    4       uint32   Compressed Data Size (bytes)
0x06    4       uint32   Uncompressed PCM Data Size (bytes)
0x0A    1       uint8    Flags (bit 0: stereo, bit 1: 16-bit)
0x0B    1       uint8    Compression Type (0 = PCM, 1 = WS-ADPCM, 2 = IMA)

Key fields include:

• Sample Rate: The playback frequency, most commonly 22,050 Hz for unit speech and sound effects in C&C and Red Alert.
• Flags:
  • (flags & 0x01) != 0: Indicates stereo (2 channels) vs mono (1 channel).
  • (flags & 0x02) != 0: Indicates 16-bit audio vs 8-bit audio.
• Compression Type:
  • 0: Uncompressed raw PCM samples.
  • 1: Westwood's custom ADPCM (WS-ADPCM / ws-snd1).
  • 2: Standard IMA-ADPCM (DVI ADPCM).

Chunk-Based Stream Architecture

Following the 12-byte header, Westwood AUD files are structured as a series of contiguous chunk blocks:

• Chunk Compressed Size (2 bytes): Number of bytes in this compressed audio block.
• Chunk Decompressed Size (2 bytes): Expected uncompressed byte length of this block.
• Audio Payload: The compressed or raw bytes for this block.

This chunked design allowed 1990s game engines to stream audio from slow CD-ROM drives directly into small sound card ring buffers with minimal RAM overhead.

Decoding WS-ADPCM and IMA-ADPCM

Both Westwood WS-ADPCM and IMA-ADPCM compress audio to 4 bits per sample (a 4:1 compression ratio compared to 16-bit linear PCM):

• Each byte in the compressed chunk contains two 4-bit nibbles:
  • Low nibble: byte & 0x0F
  • High nibble: (byte >> 4) & 0x0F
• For each nibble, the decoder references step size and index adjustment tables to predict the delta change:
  • If the sign bit (bit 3) is set, the delta is subtracted from the current sample accumulator.
  • Otherwise, the delta is added to the accumulator.
  • The accumulator is clamped to the 16-bit range ($-32768 \dots 32767$).
  • The step index is updated for the next sample based on the magnitude of the current nibble.

Wrapping the decoded samples into a standard 44-byte RIFF WAVE header yields clean, universally playable 16-bit linear PCM audio.

100% In-Browser Audio Extraction

Extracting audio from nostalgic games shouldn't require installing legacy DOS utilities or suspicious executable binaries.

convrtr's Westwood AUD to WAV tool decodes everything client-side:

• Supports 8-bit and 16-bit WS-ADPCM, IMA-ADPCM, and raw uncompressed AUD streams.
• Handles both chunked and flat Westwood stream variants.
• Preserves native sample rate or resamples cleanly to 44.1 kHz CD audio.
• Operates 100% locally with zero server uploads, keeping your retro gaming assets private.