Spectrum Analyzer Measurement per IEC 60268-16

Spectrum Analysis for STI

While STI is a modulation-domain metric, the frequency spectrum of the reproduced signal determines the energy available in each octave band for modulation transfer. Spectrum analysis reveals imbalances that degrade specific STI bands.

STIPA Signal Verification

• The STIPA test signal has approximately equal energy per octave band (pink-noise-like spectrum)
• Verify that the PA system reproduces this spectrum faithfully
• Large deviations (more than 6 dB) indicate EQ problems or speaker bandwidth limitations
• The 2-4 kHz region is critical for consonant intelligibility

Noise Spectrum Identification

1. Capture the ambient noise spectrum at listener positions
2. Compare against the STIPA signal spectrum to find bands where SNR is inadequate
3. Bands with SNR below 10 dB will have significantly reduced MTF
4. Low-frequency noise (HVAC) typically affects the 125-500 Hz bands

PA System Equalization for STI

Use spectrum analysis to guide EQ adjustments that improve STI. Focus on boosting bands where the speech spectrum is weak relative to noise, and attenuating bands where the system excites room resonances that reduce modulation depth.

Common Mistakes

• Optimizing the spectrum for music flatness instead of speech intelligibility
• Boosting bass frequencies that excite room modes and increase reverberation
• Not measuring the noise spectrum separately from the signal spectrum

SonaVyx Workflow

Analyze the system spectrum with the SonaVyx spectrum analyzer. Measure STI with the STI tool. Check system transfer function with the TF analyzer. Verify levels with the SPL meter. Run AI diagnostics for optimization suggestions. See our learning modules for PA optimization tutorials.