Field Story

Echo Canyon: When Delay Towers Fight Each Other

A 15,000-seat sports arena installed delay towers at three distances from the stage. Audience members near the second tower heard a distinct echo because the delay was set 28 ms too short. Transfer function coherence dropped to 0.3 in the overlap zone. After measuring propagation delay with the delay finder tool and correcting each tower to within 1 ms, coherence improved to 0.85 and the echo disappeared.

Sports Arena

Coherence Measurement per AES-2id

TL;DR

Coherence is the single most important quality indicator in AES-2id system alignment. The magnitude-squared coherence function tells you at which frequencies your transfer function measurement is reliable and where noise, reverberation, or nonlinearity corrupts the data. AES-2id practitioners never make EQ decisions at frequencies where coherence is below 0.85. SonaVyx displays coherence alongside the magnitude and phase response in the transfer function view, providing the quality-gating information needed for confident alignment decisions. High coherence means your measurement reflects the system response; low coherence means the room or noise dominates.

Coherence in System Alignment

Coherence quantifies the linear relationship between the reference signal and the measured response. In AES-2id alignment, it tells you which frequencies you can trust and which you should ignore when making EQ decisions.

Interpreting Coherence Values

  • Above 0.9: excellent, measurement is highly reliable
  • 0.7 to 0.9: good, minor uncertainty but usable for EQ decisions
  • 0.5 to 0.7: marginal, proceed with caution
  • Below 0.5: unreliable, do not make EQ decisions based on this data

Causes of Low Coherence

  1. Excessive reverberation (reverberant energy uncorrelated with source)
  2. High ambient noise (noise uncorrelated with reference signal)
  3. Nonlinearity in the system (clipping, limiting, speaker distortion)
  4. Time variance (moving sources, changing temperature, audience movement)
  5. Insufficient averaging (more averages improve coherence)

Improving Coherence

If coherence is low, try: increasing the source level, moving the microphone closer to the speaker, increasing the number of averages, or measuring during quieter conditions. You cannot fix low coherence with EQ.

Coherence and EQ Decisions

Only apply EQ corrections at frequencies where coherence exceeds your confidence threshold. At frequencies with low coherence, the transfer function magnitude may show dips or peaks that are measurement artifacts, not system problems.

Common Mistakes

  • Applying EQ at frequencies with low coherence, chasing measurement noise
  • Not displaying coherence alongside the magnitude response
  • Confusing coherence with signal-to-noise ratio (they are related but not identical)

SonaVyx Tools

The SonaVyx transfer function displays coherence alongside magnitude and phase. Monitor levels with the SPL meter. Check with the RTA for spectral overview. Identify issues using the problem detector. Get AI recommendations from the diagnostic engine. Follow the PA tuning workflow.

Standard Reference

AES-2id:

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Last updated: March 19, 2026