Any echo-producing system inevitably exhibits frequency power fluctuations

Evidence

The fluctuations are intrinsic: as long as there are echoes, there will be power fluctuations. This applies to power spectra, which are “point A back to point A” autocorrelations, as well as transfer spectra, which are “point A to point B” cross-correlations. — Eric J. Heller, Why You Hear What You Hear- An…, 1163

Categorization

• DEFINE: Gives a clean conceptual distinction between autocorrelation (power) and cross-correlation (transfer) spectra.
• corroborated: 2 independent passages support this claim — Eric J. Heller, Why You Hear What You Hear- An…, 1163
• XREF: connects to: A returning echo creates power-spectrum peaks spaced by its inverse time — Eric J. Heller, Why You Hear What You Hear- An…, 1096; Echo interference creates sinusoidal power fluctuations that average to zero; Power fluctuations persist even where resonances overlap completely — Eric J. Heller, Why You Hear What You Hear- An…, 1154