Coherence Measurement per ANSI S1.4

Coherence for System Validation

ANSI S1.4 specifies the linear operating range and noise floor of measurement instruments. Coherence provides a real-time check that your system operates within these bounds during actual measurements.

Linearity Verification

• A linear system produces coherence near 1.0 across the measurement bandwidth
• Coherence drops at frequencies where the system introduces distortion
• If coherence drops when you increase the source level, the system is clipping
• If coherence drops when you decrease the source level, you are approaching the noise floor

Noise Floor Detection

1. Coherence drops at frequencies where the signal approaches the measurement noise floor
2. This reveals the practical frequency-dependent dynamic range of your system
3. ANSI S1.4 specifies minimum dynamic range, and coherence tells you where you actually are
4. Low-frequency coherence is typically the first to degrade due to higher environmental noise

Practical Application

Before any critical measurement session, run a coherence check with a known signal. This verifies that your complete measurement chain, from microphone through preamp through ADC through processing, is operating within its ANSI S1.4 specified performance envelope.

Common Mistakes

• Not checking coherence before beginning a measurement session
• Ignoring coherence drops that indicate system overload
• Assuming the measurement system is linear without verification

SonaVyx Approach

Check coherence in the SonaVyx transfer function view. Verify levels with the SPL meter. Use the RTA for spectral monitoring. Check for issues with the problem detector. Run AI diagnostics. See our learning modules for measurement system validation.