Transfer Function Measurement per IEC 61672-1

Transfer Function for Meter Verification

IEC 61672-1 specifies the ideal frequency response for A, C, and Z weighting networks with tolerance limits at each 1/3-octave frequency. Transfer function measurement provides a direct way to verify compliance.

Measurement Procedure

1. Generate a flat pink noise reference signal
2. Route it through the device under test (the SPL meter or weighting network)
3. Capture both the reference (input) and the weighted (output) signals
4. Calculate the transfer function H(f) = Output/Input
5. Compare the magnitude response against IEC 61672-1 tolerance curves

A-Weighting Verification Points

Key frequencies where IEC 61672-1 specifies tight tolerances:

• 1 kHz: 0.0 dB (reference, Class 2 tolerance plus or minus 1.4 dB)
• 500 Hz: -3.2 dB nominal
• 2 kHz: +1.2 dB nominal
• 125 Hz: -16.1 dB nominal
• 63 Hz: -26.2 dB nominal (Class 2 tolerance plus or minus 5.0 dB)

Coherence as Quality Indicator

The coherence function from the transfer function measurement indicates measurement quality. For meter verification, coherence should exceed 0.95 across the entire measurement bandwidth. Low coherence indicates noise contamination or nonlinear behavior.

Common Mistakes

• Using too short an averaging time, resulting in low coherence
• Not accounting for the microphone frequency response in the measurement chain
• Comparing against the wrong tolerance class
• Measuring at too low a level where noise floor affects results

SonaVyx Workflow

Use the SonaVyx transfer function analyzer for high-resolution frequency response measurement. Verify levels with the SPL meter. Check the RTA for real-time spectral monitoring. The problem detector can identify anomalies in the response. Review AI diagnostics for automated analysis. See our learning modules for measurement fundamentals.