Understanding Cepstral Peak Prominence (CPP): ASHA's Recommended Standard for Voice Assessment
🎯 Key Takeaways
- ASHA recommends CPP as the primary acoustic measure for dysphonia assessment
- CPP works where traditional measures fail: severely dysphonic voices, continuous speech, no pitch tracking needed
- Clinical cutoffs (software-specific): For Praat/PhonaLab CPPS: <14.45 dB (vowel) or <9.33 dB (speech) suggests dysphonia
- Clinical advantage: More robust correlation with perceived dysphonia severity
- Calculate CPP instantly with our free analyzer tool
In recent years, Cepstral Peak Prominence (CPP) has emerged as the most robust acoustic measure for assessing voice quality. The 2018 ASHA expert panel specifically recommended CPP as the primary acoustic measure for dysphonia assessment, replacing traditional perturbation measures like jitter and shimmer. Yet many clinicians still reach for those traditional measures—measures that often fail precisely when we need them most: with severely dysphonic voices.
If you were trained on jitter and shimmer, you're not alone. Most speech-language pathology programs still emphasize these traditional measures. But the field has shifted, and understanding CPP is now essential for evidence-based voice assessment.
Let me explain what CPP actually measures, why it's become ASHA's recommended standard, and, most importantly, how to use it effectively in your clinical practice—including which free tools are available and how to interpret software-specific values correctly.
The Problem with Traditional Measures
For decades, jitter (cycle-to-cycle pitch variability) and shimmer(cycle-to-cycle amplitude variability) were the go-to acoustic measures. They made intuitive sense: a smooth, periodic voice signal should have minimal perturbation, while a rough or hoarse voice would show increased variability.
But there's a fundamental problem: both measures require accurate fundamental frequency (F0) tracking.
The Catch-22 of Perturbation Measures
Jitter and shimmer work beautifully for mildly dysphonic voices, but fail catastrophically for severely dysphonic voices—where you need objective measures most. When the voice becomes buried in noise (severe breathiness, roughness, or hoarseness), there isn't enough periodic information for the algorithm to identify individual vocal fold cycles.
This creates a clinical nightmare: your most severe patients—those who most need quantifiable evidence of disorder—are the ones whose voices can't be reliably measured with traditional methods.
Additional limitations of jitter and shimmer:
- Valid only for sustained vowels: Can't assess voice quality during continuous speech, which is how patients actually communicate
- Weak correlation with perception: The numbers don't always match what clinicians hear perceptually
- High variability: Small changes in recording conditions or analysis settings can produce very different results
- Limited clinical utility: Knowing jitter is 2.5% vs. 1.5% doesn't directly guide treatment decisions
Enter Cepstral Peak Prominence (CPP)
CPP emerged from signal processing research as a more robust alternative. The American Speech-Language-Hearing Association (ASHA) 2018 expert panelspecifically recommended CPP as the primary acoustic measure for voice assessment, particularly for dysphonic voices. This recommendation remains current as of 2025.
What is CPP?
Without getting too technical: CPP measures the prominence of harmonic structure in the voice signal relative to background noise. Think of it as quantifying how "clear" the harmonic peaks are in the voice spectrum.
Conceptual Framework
Think of the voice spectrum as a city skyline. In a healthy voice, harmonic peaks (the buildings) stand tall and distinct above the noise floor (the horizon). In dysphonia, increased aperiodic energy (fog) obscures these harmonics. CPP quantifies how prominently the harmonic structure rises above this noise floor.
Why CPP Works Better
| Feature | Jitter/Shimmer | CPP |
|---|---|---|
| Accurate pitch tracking | âś— Required (fails for severe dysphonia) | âś“ Not required |
| Valid for continuous speech | âś— No (sustained vowels only) | âś“ Yes (connected speech is ideal) |
| Correlates with perception | âš Weak to moderate | âś“ Strong (r = 0.60-0.85) |
| Recording sensitivity | âš High | âś“ More robust |
| Works across voice types | âś— Struggles with breathy/rough voices | âś“ Reliable for all dysphonia types |
Clinical Cutoffs (Software-Specific)
CPP vs. CPPS – Critical Distinction
Modern tools like Praat and PhonaLab calculate CPPS (smoothed CPP), which averages measurements across multiple time windows for more stable results. CPPS values are typically 3-4 dB higher than unsmoothed CPP (used by ADSV). Always use software-specific norms!
| Software | Vowel Cutoff | Speech Cutoff |
|---|---|---|
| Praat / PhonaLab (CPPS) | <14.45 dB | <9.33 dB |
| ADSV (CPP) | <11.46 dB | <6.11 dB |
Values below cutoffs suggest dysphonia. Higher values = healthier voice quality.
Common Questions About CPP
Q: Can I calculate CPP with free software?
Yes! Praat is free (though it has a learning curve). Our PhonaLab Voice Analyzer also provides free CPP calculation with AI interpretation and PDF reports—no installation required.
Q: Why are my Praat/PhonaLab values higher than values I see in papers?
This is normal! Praat and PhonaLab calculate CPPS (smoothed CPP), which is typically 3-4 dB higher than CPP from ADSV. Papers using different software report different ranges. Always check which software was used and apply software-matched normative values.
Q: Is CPP valid for telehealth recordings?
Yes, with proper protocols. Recent research shows smartphone recordings achieve correlations >0.90 with clinical equipment for CPP when standardized methods are followed. Key factors: quiet environment, consistent device/distance, high-quality recording settings.
Q: Should I report CPP to referring physicians?
Absolutely. Many ENTs are familiar with CPP from the literature. Include a brief interpretation: "CPP of 8.2 dB indicates moderate dysphonia; values >14 dB are typical for healthy voice." Always specify which software you used.
Bottom Line: Why CPP Matters for Your Practice
- 1CPP is ASHA's recommended primary acoustic measure for dysphonia assessment (2018 guidelines, still current)
- 2SOFTWARE MATTERS: Praat/PhonaLab CPPS values are 3-4 dB higher than ADSV CPP
- 3Track trends over time rather than fixating on single values
- 4Use alongside perceptual assessment and laryngoscopy for comprehensive evaluation
- 5Works where jitter/shimmer fail: moderate-to-severe dysphonia, continuous speech
🎤 Calculate CPP on Your Patient Recordings
Upload any voice recording and get instant CPPS analysis with AI-powered clinical interpretation. Includes software-specific normative comparisons and professional PDF reports.
Try Free Voice Analyzer →Includes CPP/CPPS, F0, jitter, shimmer, HNR, and AVQI multiparametric assessment
⚠️ Clinical Documentation Tool
The information in this article is provided for educational purposes and clinical documentation support. Acoustic measures like CPP are intended to supplement—not replace—comprehensive voice evaluation including perceptual assessment, patient history, and laryngoscopic examination when indicated. All clinical decisions should be made by qualified healthcare professionals based on the complete clinical picture. PhonaLab tools are designed for professional use and do not provide medical diagnoses.
References & Further Reading
- Patel RR, Awan SN, Barkmeier-Kraemer J, et al. (2018). Recommended Protocols for Instrumental Assessment of Voice: American Speech-Language-Hearing Association Expert Panel. American Journal of Speech-Language Pathology, 27(3), 887-905.
- Murton O, Hillman R, Mehta D (2020). Cepstral Peak Prominence Values for Clinical Voice Evaluation. American Journal of Speech-Language Pathology, 29(3), 1596-1607.
- Maryn Y, Corthals P, Van Cauwenberge P, Roy N, De Bodt M. (2010). Toward improved ecological validity in the acoustic measurement of overall voice quality. Journal of Voice, 24(5), 540-555.
- ASHA Practice Portal: Voice Disorders -Assessment and Treatment
Dr. Jorge C. Lucero
Professor of Computer Science, University of BrasĂlia
Dr. Lucero has 30+ years researching voice production and vocal fold dynamics. He created the PhonaLab suite of free voice analysis tools to make professional acoustic assessment accessible to clinicians worldwide. Updated November 2025.