Voice problems that require voice analysis most commonly originate from the vocal folds or the laryngeal musculature that controls them, since the folds are subject to collision forces with each vibratory cycle and to drying from the air being forced through the small gap between them, and the laryngeal musculature is intensely active during speech or singing and is subject to tiring.
Movements in the vocal cords are rapid, fundamental frequencies are usually between 80 and 300 Hz, thus preventing usage of ordinary video.
Stroboscopic, and high-speed videos provide an option, but to see the vocal folds a fiberoptic probe leading to the camera must be positioned in the throat, which makes speaking difficult.
In addition, placing objects in the pharynx usually triggers a gag reflex that stops voicing and closes the larynx.
indirect methods are currently inverse filtering of either microphone or oral airflow recordings and electroglottography (EGG).
[citation needed] In inverse filtering, the speech sound (the radiated acoustic pressure waveform, as obtained from a microphone) or the oral airflow waveform from a circumferentially vented (CV) mask is recorded outside the mouth and then filtered by a mathematical method to remove the effects of the vocal tract.
This method estimates the glottal input of voice production by recording output and using a computational model to invert the effects of the vocal tract.
Another active research topic in medical voice analysis is vocal loading evaluation.
A professional voice analyzer has a trained ear and can block out excess variants that can be deceptive from the results.
Spectral analysis visualizes the frequency of the audio for an examiner to pick out features of interest.
Experts in forensic voice analyze recordings by examining transmitted and stored speech, enhancing it and decoding it for criminal investigations, court trials, and federal agencies.
Oftentimes, samples have poor sound quality due to environmental factors such as wind or movement.
Different solutions for poor comprehensibility are done using computer programs that allow the user to filter and eliminate noise.
The interpretation process might include piecing together a timeline, transcribing the dialog, and identifying unknown or unintelligible sounds in the audio recording.
This is when the identity of a speaker is unknown, and has to be identify from an array of other voices or suspects when pertaining to a crime investigation or court trial.