Nasometry Devices: Instrumentation for Objective Voice Analysis

 

Nasometry Devices

Nasometry is an objective technique for analyzing the acoustic characteristics of the voice and its nasal quality. Nasometry devices utilize specialized microphones and sensors to identify and quantify the resonance patterns in speech. By measuring nasal airflow and acoustic resonances, nasometry provides quantitative data about the balance between oral and nasal voice production. This objective data can be useful for diagnosing voice disorders, tracking progress during voice therapy, and evaluating the effectiveness of surgical interventions.

How Nasometry Works

Nasometry systems work by simultaneously recording the acoustic signal from the microphone as well as the nasal airflow signal from a nasal cannula or thermistor. The microphone captures the speaker's full speech waveform, while the nasal sensor detects any airflow through the nose. By comparing these two signals, the nasometer can identify periods of voiced speech and determine the nasalance score - a percentage of how much nasal resonance is present.

The nasometer divides each vowel interval into 10-millisecond frames and calculates nasalance on a frame-by-frame basis. It is able to ignore periods of silence, pauses, and unvoiced consonants. Modern digital nasometers also normalize the nasalance score based on speaking volume and other acoustic factors. This frame-by-frame analysis allows nasometry reports to provide detailed breakdowns of resonance patterns over time within an utterance or connected speech sample.

Clinical Applications of Nasometry

One of the main clinical uses of nasometry is to objectively diagnose and classify voice disorders with a nasal quality or nasal air emission. Conditions like nasal regurgitation of air, nasal polyps, cleft palate, and repaired vocal fold lesions can disrupt the natural balance between oral and nasal resonance. Nasometry provides quantitative confirmation of nasalization and tracks pre- versus post-treatment scores.

Nasometry is also valuable for managing and monitoring the progress of patients undergoing speech therapy or vocal rehabilitation. Baseline nasometry establishes a target for oralization exercises and resonance retraining. Repeat testing charts improvements and helps determine when vocal technique has been properly altered. For those pursuing surgical options, nasometry data before and after surgery reveals the degree of normalization achieved.

Beyond diagnosing and monitoring individual patients, nasometry allows clinicians to compare voice qualities across different populations. Normative data from controlled nasometry studies provides benchmarks for typical nasalance in various accents, age groups, and genders. Objective norms help avoid subjectivity in perceiving resonance and set standards for determining abnormal nasalization.

Technical Considerations in Nasometry

Proper nasometry requires high-quality instrumentation, standardized protocols, and controlled testing environments. Variability between nasometers must be minimized for comparisons over time and between clinicians to be valid. Early nasometry systems suffered from inconsistencies, but modern digital devices have much higher validity and reliability.

Speech samples must follow standardized text passages, like the Nasality Assessment Procedure (NAP), to ensure replicable testing. Speaking rate, volume, posture, and other variables need to be controlled. Ambient noise and acoustic reflections can degrade the nasal airflow and acoustic signals if not addressed. Clinicians must be trained to position the nasal cannula correctly and avoid signal contamination.

Contralateral routing of signal cancellation techniques help eliminate microphone bone conduction biases that could influence nasometry scores. Advances in calibration, digital signal processing, and normalization methods continue to improve the accuracy and usefulness of clinical nasometry for objective voice analysis. With proper equipment and protocols, nasometry delivers valuable quantitative data for diagnosis and management of nasal voice disorders.

New Applications of Nasometry

As nasometry techniques and instrumentation advance, new applications are being explored. Recent research applies nasometry to accent analysis, evaluating speakers of different primary languages or dialects. Some studies even use nasometry to aid voice identification for forensic purposes.

Nasometry may also help optimize pressurized speech valves used for alaryngeal voice rehabilitation after total laryngectomy. Precise pressure and resonance adjustments can be monitored objectively with nasometry. There is also potential to incorporate nasometry into biofeedback therapies that use visual displays of real-time nasalance for patients learning to control resonance.

With growing evidence supporting the clinical utility of nasometry devices, its use will likely increase as an objective standard of care. Continued technical refinements seek to make the instrumentation simpler to use in more clinical settings. As nasometry demonstrates benefits across a wider range of voice disorders and applications, it will further validate its role in comprehensive voice analysis and management.