White noise has autocorrelation only at zero time shift.

Evidence

Strictly periodic signals last forever and are perfectly correlated with themselves: they repeat at multiples of the period. At the other extreme, a signal might have no correlation with itself from moment to moment: knowing the signal at one instant says nothing about it the next; such a signal is said to correspond to white noise (noise that has power in all regions of the audio spectrum). The autocorrelation for white noise has a peak only at τ = 0 and falls immediately to 0 for τ ≠ 0. — Eric J. Heller, Why You Hear What You Hear- An…, 411

Categorization

• DEFINE: Defines the autocorrelation extremes: perfect periodic signals versus white noise.
• XREF: Connects to physical accounts of hiss and noise floors in audio.
• CANDY: ‘White noise is so uncorrelated with itself that knowing one instant tells you nothing about the next.’