In the world of voice analysis and clinical voice assessment, precision and consistency are paramount. Two commonly used acoustic measures — CPP (Cepstral Peak Prominence) and CPPS (Cepstral Peak Prominence Smoothed) — have emerged as leading tools for evaluating vocal quality. These measurements are critical for diagnosing voice disorders, tracking treatment progress, and providing objective data in both research and clinical practice.
However, a common question remains: Should you use CPP or CPPS? The answer depends on several factors including the type of vocal task, the need for reliability across different speech contexts, and the goal of your evaluation.
Phonalyze calculates both CPP and CPPS automatically — for every vocal task.
Whether it’s a sustained vowel or spontaneous speech, you get accurate, side-by-side data to track your patient’s voice health with confidence.
Quick Answer
- Use CPP when you’re analyzing controlled, sustained vowel phonation (like a prolonged “ah” sound). It’s effective for specific, structured vocal tasks where consistency is maintained.
- Use CPPS for evaluating more natural, connected speech or when comparing results across different speech contexts. It’s especially favored in clinical settings due to its reliability, robustness, and lower sensitivity to variations in task type.
Introduction to CPP and CPPS
What Are They?
CPP (Cepstral Peak Prominence) and CPPS (Cepstral Peak Prominence Smoothed) are quantitative acoustic measures used to assess the quality of a voice signal. They are both derived from the cepstrum, a mathematical representation of sound that captures information about the periodic structure (or harmonicity) of a voice.
These measurements are particularly valuable because they allow clinicians and researchers to evaluate vocal health objectively, moving beyond subjective perceptual judgments (like simply saying a voice sounds “rough” or “breathy”).
CPP (Cepstral Peak Prominence): A Closer Look
Definition
CPP quantifies the strength or prominence of the peak in the cepstral domain, which corresponds to the harmonic structure of the voice. In layman’s terms, it tells you how strong and periodic a voice signal is, relative to the noise around it.
How It Works
During voice analysis, the cepstral domain is used to detect periodic features in the signal (such as pitch or vocal fold vibration patterns). A prominent peak in this domain indicates clear periodicity, which is a sign of a healthy, regular vocal fold vibration.
CPP is calculated as the difference in decibels (dB) between the cepstral peak and the regression line fitted across the spectrum. A higher CPP reflects a cleaner, more periodic voice signal, while a lower CPP points to vocal irregularities such as breathiness or hoarseness.
Clinical Interpretation
- High CPP = Good vocal quality, strong periodicity, healthy vocal fold behavior.
- Low CPP = Disordered voice, dysphonia, roughness, vocal fatigue, or vocal fold pathology.
When to Use CPP
CPP is especially useful when:
- You’re analyzing sustained vowels (like a long-held “ah”).
- The speech sample is highly controlled with minimal variability.
- You’re conducting lab-based voice evaluations with consistent vocal tasks.
CPPS (Cepstral Peak Prominence Smoothed): A Closer Look
Definition
CPPS is an enhanced version of CPP that incorporates smoothing in its calculation. This smoothing is applied to reduce fluctuations and irregularities in the voice signal, especially those caused by variations in connected speech or spontaneous vocal tasks.
Why Smoothing Matters
In real-world speech, variability is the norm. From subtle pitch shifts to breathiness and articulation changes, natural speech introduces inconsistencies that can distort voice analysis. CPPS addresses this by stabilizing the measurement, making it more consistent and reliable.
How It Works
Just like CPP, CPPS is derived from the cepstrum. However, before calculating the peak prominence, CPPS applies a moving average smoothing algorithm across both time and quefrency domains (quefrency is the x-axis in a cepstrum plot). This results in less sensitivity to noise and variability, especially in non-sustained, natural speech tasks.
Clinical Interpretation
- High CPPS = Healthy, periodic, stable voice.
- Low CPPS = Irregular vocal fold vibration, disordered voice, reduced vocal efficiency.
When to Use CPPS
CPPS is ideal when:
- You are analyzing connected speech (like reading a sentence or spontaneous speech).
- You need robust and repeatable results across different vocal tasks.
- You’re conducting clinical evaluations with diverse patient populations.
CPP vs CPPS: Key Differences at a Glance
| Feature | CPP | CPPS |
|---|---|---|
| Calculation | Direct cepstral peak measurement | Cepstral peak with smoothing |
| Best suited for | Sustained vowel phonation | Continuous, connected speech |
| Sensitivity | More sensitive to variability and noise | Less sensitive due to smoothing |
| Clinical use | More common in research/lab settings | Preferred in clinical evaluations |
| Stability across tasks | Lower | Higher |
| Reporting tool (Phonalyze) | Reported | Reported |
CPP (Raw Analysis)
CPPS (Smoothed Analysis)
CPP (Raw Analysis)
CPPS (Smoothed Analysis)
Why CPPS Is Preferred in Clinical Practice
In recent years, CPPS has become the preferred acoustic measure in many clinical environments, and for good reason. Its smoothing process leads to greater inter-rater and intra-rater reliability, making it more robust across different clinicians and patient tasks.
Benefits of CPPS in Clinical Use:
- Works well for both sustained vowels and continuous speech.
- Shows greater consistency in repeated measurements.
- Better correlates with perceptual assessments of voice quality.
- Less affected by external noise, recording quality, or minor inconsistencies in speech.
This is why platforms like Phonalyze report both CPP and CPPS but often encourage the use of CPPS when tracking patient outcomes or making clinical judgments.
Reporting in Phonalyze: CPP and CPPS Together
Modern acoustic analysis tools like Phonalyze calculate both CPP and CPPS in their reports. This dual-reporting approach provides clinicians and researchers with flexibility:
- Use CPP for structured tasks like sustained phonation or pre/post-therapy comparison on vowels.
- Use CPPS when evaluating patient speech in naturalistic settings or conducting comprehensive voice assessments.
This enables you to tailor your analysis based on the nature of the speech task and the clinical question at hand.
Real-World Example
Let’s say you are evaluating a patient recovering from vocal fold surgery. In the early sessions, you ask them to produce a long “ah” sound. CPP might be appropriate here because the task is sustained and controlled.
Later, as the patient progresses, you ask them to read a passage aloud or engage in conversational speech. These tasks are more natural and variable. In this case, CPPS offers greater reliability and consistency, helping you track the patient’s progress in more realistic vocal scenarios.
Research Insights
Recent studies have highlighted the efficacy of CPPS in clinical voice assessments. For instance, a study published in the Journal of Voice established normative CPPS values and demonstrated its high sensitivity and specificity in detecting dysphonia. The research concluded that CPPS is a reliable measure for distinguishing between normal and disordered voices, particularly in running speech samples.
Moreover, the American Journal of Speech-Language Pathology emphasized the importance of considering factors such as vowel quality, loudness, and speaker demographics when interpreting CPP values. These variables can significantly influence the measurements, underscoring the need for standardized assessment protocols.
Practical Considerations
When choosing between CPP and CPPS, consider the following:
- Assessment Context: Use CPP for controlled, sustained vowel tasks and CPPS for natural, connected speech.
- Measurement Consistency: CPPS offers greater stability across different tasks and speaking conditions.
- Clinical Objectives: For comprehensive voice evaluations and monitoring treatment outcomes, CPPS provides more reliable data.
Conclusion: Which One Should You Use?
Both CPP and CPPS are valuable tools in the field of voice assessment. The decision to use one over the other should be informed by:
- The type of vocal task being analyzed.
- The clinical or research context.
- The need for reliability and stability across speech types.