.WV File Format – Decorrelation

Terms and deltas (ID_DECORR_TERMS)

One byte per pass, at most 16:

Any other term value is invalid, as is a negative term in a mono block.

Weights (ID_DECORR_WEIGHTS)

A signed byte for each pass, or two in a stereo block, for channels A and B. Weights are stored from the last pass backwards, and any pass left over has a weight of 0.

weight = byte × 8
if weight > 0:  weight += (weight + 64) >> 7

This gives the range ±1024. The prediction is applied and the weight adapted as follows:

apply(w, s)    = (w × s + 512) >> 10

update(w, delta, source, result):
    if source and result are both nonzero:
        sign = (source ^ result) >> 31   (all 1s when they differ in sign, else 0)
        w = (delta ^ sign) + (w − sign)

In other words, the weight moves up by delta when the signs agree, and down when they differ. The cross-channel terms clip the weight to ±1024.

Sample histories (ID_DECORR_SAMPLES)

Each value is 16 bits, little-endian and signed, in the compact logarithmic form the wp_exp2s function expands. Passes run from the last backwards, while bytes remain.

In stream version 0x402 with the hybrid flag, the payload starts with one or two error values. The sub-block must use all of its bytes exactly.

Stereo

With the JOINT_STEREO flag, the samples are reversed from mid and side after all passes:

R = R − (L >> 1)
L = L + R

With the FALSE_STEREO flag, a single channel is decoded and copied to both.

The sample CRC

The header’s crc is a running calculation over the final samples, with 32-bit wrap-around:

The extra-bits form belongs to the extended stream’s own CRC, which is stored at the start of the WVX data.