Signs

Detects: Acoustic indicators of stress and nervousness — elevated laryngeal tension, altered respiratory patterns, and shifts in vocal tract dynamics associated with sympathetic arousal.

Detection rationale: Stress and nervousness activate the sympathetic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis, producing physiological changes that increase laryngeal muscle tension, alter respiratory support for speech, and shift vocal tract resonance characteristics — all producing measurable acoustic changes. Stress is one of the most extensively studied states in speech biomarker research, with studies establishing both direct (HPA-axis) and indirect (autonomic) pathways to vocal change.

Acoustic indicators: Elevated pitch_variability from heightened laryngeal muscle tension; increased speech_rate driven by sympathetic arousal; reduced voice_clarity_hnr (tighter, less clear vocal quality); changes in loudness_mean reflecting altered respiratory drive; formant frequency shifts from vocal tract tension.

Evidence: Three or more peer-reviewed voice-based studies; meta-analyses with cortisol biomarker validation; findings replicated across two or more independent research groups.

Detects: Acoustic indicators of generalized and social anxiety — vocal fold irregularity under autonomic tension, altered breath support, and characteristic prosodic patterning.

Detection rationale: Anxiety activates the sympathetic branch of the autonomic nervous system, producing shallow breathing, increased laryngeal muscle tension, and reduced respiratory support for phonation. These changes are observable even in neutral speech content, making voice a useful index of anxious arousal independent of what is being said. The indirect autonomic pathway between anxiety and vocal change is well characterized in psychophysiology literature.

Acoustic indicators: Increased voice_jitter and voice_shimmer reflecting vocal fold irregularity under tension; altered pitch_variability from heightened laryngeal tension; changes in pause_duration_mean driven by respiratory disruption; loudness_mean shifts from altered breath support; spectral features reflecting vocal tract changes.

Evidence: Three or more peer-reviewed studies; JMIR validation; replicated across independent groups. Indirect autonomic pathway validated.

Detects: Acoustic and linguistic indicators of cognitive impairment — word-finding difficulty, disrupted speech planning, reduced verbal fluency, and altered speech timing.

Detection rationale: Cognitive impairment affects the neural pathways responsible for speech production, verbal fluency, memory retrieval, and semantic processing. Degradation in these systems produces measurable changes in the temporal structure of speech: more frequent and longer pauses reflecting word-finding difficulty, reduced speech rate from slower cognitive processing, and changes in lexical diversity and semantic coherence that are detectable from short speech samples.

Acoustic indicators: Increased pause_duration_mean and pause frequency reflecting word-finding difficulty; reduced speech_rate from slower cognitive processing; changes in articulation_rate from disrupted planning; linguistic features (lexical diversity, semantic coherence) contribute significantly alongside acoustic indicators.

Evidence: Five or more peer-reviewed publications; ADReSS challenge benchmark; replicated across multiple independent research groups; prospective validation studies including large-cohort MCI detection from speech.

Detects: Acoustic indicators of chronic obstructive pulmonary disease — impaired respiratory function and its downstream effects on breath support, phonation duration, and voice quality.

Detection rationale: COPD reduces lung function and respiratory capacity, directly limiting the breath support available for speech. Reduced airflow produces shorter phrase lengths before breath replenishment, more frequent breath-driven pauses, and breathier vocal quality from incomplete glottal closure under low subglottal pressure. Air trapping and altered respiratory mechanics further affect the consistency of phonation across a breath group.

Acoustic indicators: Reduced voice_clarity_hnr from breathier, less complete phonation; altered loudness_mean from reduced respiratory drive; changes in articulation_rate from shorter breath groups; increased pause_duration_mean for breath replenishment.

Evidence: 15–20 dedicated voice-based COPD studies; JMIR validation; large-scale respiratory biomarker validation (1.5M voice data points, mean AUC 0.899); replicated across independent research groups.

Detects: Acoustic indicators of major depressive disorder — psychomotor slowing, reduced vocal energy, flattened prosody, and altered speech timing observable even in neutral speech.

Detection rationale: Depression affects the limbic system and psychomotor pathways, producing psychomotor retardation that directly slows speech rate, lowers vocal energy output, flattens pitch variability, and increases pause frequency. Emotional blunting reduces prosodic expressiveness, producing a characteristic monotone quality. These changes are detectable from neutral speech content and do not require discussion of emotional topics, making voice analysis well suited for low-barrier screening.

Acoustic indicators: Reduced loudness_mean from psychomotor slowing; decreased speech_rate from cognitive and motor retardation; lowered pitch_variability from emotional blunting; increased pause_duration_mean; reduced articulation_rate. MFCCs and formant structure further differentiate depressed from healthy speech.

Evidence: A primary Amplifier research domain; multiple Amplifier peer-reviewed publications; JMIR validation with 14,898 subjects; systematic reviews confirming acoustic correlates; replicated across independent research groups.

Detects: Acoustic indicators of undiagnosed elevated blood pressure — reflecting autonomic dysregulation and vascular state changes that influence laryngeal function and vocal tract tension.

Detection rationale: Elevated blood pressure alters autonomic balance, affecting laryngeal blood flow, vocal tract tissue perfusion, and sympathetic regulation of phonation. The pathway is indirect: sustained autonomic dysregulation associated with elevated blood pressure produces measurable vocal changes that correlate with BP state. Validated BP-vocal studies, including the Klick Labs study reporting 77–84% accuracy, establish the indirect ANS pathway as reproducible. This model surfaces undiagnosed or subclinical blood pressure elevation as a supplementary signal, not as a replacement for clinical measurement.

Acoustic indicators: Subtle changes in loudness_mean, pitch_variability, and voice_jitter reflecting altered autonomic state; spectral features from vocal tract tension related to vascular and autonomic changes.

Evidence: Multiple voice-based blood pressure studies including large-cohort validation; indirect autonomic and vascular pathway confirmed across independent groups.

Detects: Acoustic indicators of physical fatigue, mental exhaustion, and malaise — reduced respiratory support, lower laryngeal muscle tone, and impaired cognitive resources for speech production.

Detection rationale: Fatigue reduces respiratory support for phonation, decreases laryngeal muscle tone, and impairs the cognitive resources required for fluent language production. The result is measurably lower vocal energy, slower articulation, more frequent pauses, and reduced voice quality. The link between fatigue and vocal change is well established across high-stakes domains: aviation and air traffic control research validated fatigue-related vocal change as a safety-critical signal, and COVID-19 prospective research further confirmed the acoustic signature.

Acoustic indicators: Reduced loudness_mean from lower respiratory drive; decreased speech_rate from reduced motor and cognitive capacity; reduced voice_clarity_hnr reflecting reduced phonation quality; increased pause_duration_mean from impaired sustained speech production.

Evidence: Amplifier peer-reviewed publication plus four or more independent peer-reviewed studies; prospective COVID-19 validation; aviation and ATC validation studies; replicated across independent research groups.

Detects: Acoustic indicators of TBI — dysarthria, slowed neural processing, and impaired respiratory-phonatory-articulatory coordination.

Detection rationale: TBI affects motor cortex function, neural signal timing, and the coordination of the respiratory, phonatory, and articulatory systems. Dysarthria — imprecise articulation from motor control damage — is a common sequela. Slowed cognitive processing produces longer response latencies and altered speech timing. Because these changes are present in the acute and post-acute phases, voice provides a non-invasive signal for clinical assessment of TBI-related speech and cognitive indicators.

Acoustic indicators: Increased voice_jitter and voice_shimmer from impaired laryngeal motor control; reduced speech_rate from slowed neural processing; increased pause_duration_mean; changes in articulation precision. Multi-session analysis enables recovery tracking. Structured verbal prompts (verbal fluency tasks, picture description) improve signal quality for this model.

Evidence: 8–12 studies with AUC 0.65–0.82; Amplifier peer-reviewed publications; validated in athletic and occupational populations.

Detects: Acoustic indicators of ADHD — speech rate variability, articulation instability, and intensity dysregulation reflecting executive dysfunction and impaired speech motor planning.

Detection rationale: ADHD affects executive function and dopaminergic circuits in the basal ganglia responsible for timing and motor control. These deficits manifest in speech as increased variability in speech rate, less consistent articulation, and irregular prosodic intensity.

Acoustic indicators: speech_rate variability from impaired motor timing; articulation consistency changes; loudness_mean irregularity from intensity dysregulation; prosodic rhythm disruptions from executive control deficits.

Evidence: 8–15 studies with AUC 0.60–0.75; Scientific Reports 2025 external validation (AUC 0.76); ADHD subtype heterogeneity and pediatric/adult differences noted. Active research pipeline.

Detects: Acoustic indicators of alcohol use disorder — effects of alcohol on the fine motor coordination of the vocal system, including impaired articulation, reduced vocal clarity, and altered speech timing.

Detection rationale: Alcohol depresses CNS function and reduces fine motor coordination, including the precise laryngeal and articulatory control required for clear speech. Sustained alcohol use produces measurable changes in articulation precision, vocal clarity, and speech timing that are detectable from voice recordings. Voice provides an objective, non-invasive signal complementary to self-report in recovery monitoring and clinical assessment contexts.

Acoustic indicators: Increased voice_jitter and voice_shimmer from impaired laryngeal motor control; reduced voice_clarity_hnr reflecting reduced phonation clarity; altered speech_rate; changes in articulation precision and timing consistency.

Evidence: Multiple voice-based studies on alcohol and vocal change; laboratory intoxication studies reporting high classification accuracy; active research pipeline for chronic use disorder detection.

Detects: Acoustic indicators associated with allergic rhinitis — nasal coupling to the vocal tract and upper airway inflammation altering resonance and vocal quality.

Detection rationale: Nasal congestion and upper airway inflammation alter the nasal coupling to the vocal tract, affecting nasality and resonance characteristics. Inflammatory changes in the upper airway may also influence laryngeal function. Voice quality changes in allergic rhinitis are documented in the clinical voice literature, and treatment of allergic rhinitis has been shown to improve acoustic voice parameters.

Acoustic indicators: Altered nasal resonance and upper airway inflammation may affect spectral balance and vocal quality, reflected in voice_clarity_hnr and pitch_variability; nasal obstruction can change intensity distribution and resonance in ways that overlap with these features.

Evidence: Voice quality changes in allergic rhinitis documented in clinical voice literature, including studies showing acoustic improvements following treatment; dedicated voice-based detection studies are limited.

Detects: Acoustic indicators of hyperandrogenism and elevated androgen levels — direct hormonal effects on vocal fold tissue that alter fundamental frequency and vocal fold dynamics.

Detection rationale: Androgens directly affect vocal fold tissue through the same mechanism responsible for voice deepening during male puberty: androgen exposure increases vocal fold mass and alters tissue composition. Elevated androgens in women with PCOS produce measurable vocal fold thickening and lowering of fundamental frequency. This is among the most direct hormonal-to-acoustic pathways in voice biomarker research, reducing reliance on indirect autonomic or behavioral mediators.

Acoustic indicators: Reduced fundamental frequency (lower pitch) from increased vocal fold mass; changes in pitch_variability from altered vocal fold tension characteristics; voice_jitter and voice_shimmer changes reflecting modified vocal fold mass and tissue properties; possible shifts in formant frequencies from vocal tract changes.

Evidence: Direct hormonal pathway; four studies in meta-analysis; 85% classification accuracy reported. Prospective clinical replication threshold for Established not yet met.

Detects: Acoustic indicators associated with overweight and obesity — vocal tract resonance changes, respiratory dynamics, and autonomic function patterns related to elevated BMI.

Detection rationale: Elevated BMI affects upper airway anatomy and respiratory mechanics. Increased soft tissue mass in the pharyngeal region alters resonance characteristics of the vocal tract. Reduced respiratory capacity from elevated BMI affects breath support and the consistency of subglottal pressure during phonation. The BMI–acoustic relationship is documented in published research.

Acoustic indicators: Changes in resonance characteristics (formant frequencies) from altered upper airway anatomy; modified voice_clarity_hnr from respiratory and phonatory changes; changes in loudness_mean; breathing pattern indicators.

Evidence: Published research on voice-based BMI prediction including a 2024 JMIR AI study; BMI–acoustic association documented across multiple studies. Prospective clinical-scale validation ongoing.

Detects: Acoustic indicators of PTSD — pitch flatness, breathy vocal quality, reduced spectral energy, and prosodic disruption reflecting HPA axis dysregulation and dorsal vagal inhibition.

Detection rationale: Chronic PTSD is associated with HPA axis flattening that reduces vocal effort and laryngeal tone. The dorsal vagal response characteristic of PTSD produces laryngeal inhibition and dampened prosodic expressiveness. Dissociation further reduces vocal dynamism. These effects produce a characteristic pattern of reduced pitch variability, breathier phonation, and flattened prosody that is detectable in neutral speech.

Acoustic indicators: Reduced pitch_variability from HPA flattening; increased breathiness reflected in voice_clarity_hnr; reduced loudness_mean from laryngeal inhibition; altered prosodic rhythm. eGeMAPS features (F0, HNR, breathiness markers) are well-matched to this mechanism.

Evidence: 10–15 studies; replicated across independent groups including prospective clinical cohorts. Anchor studies include Marmar 2019 and subsequent replications.

Detects: Acoustic indicators of psychoactive substance use — CNS effects on vocal motor control, cognitive function, and emotional state that vary in character by substance class.

Detection rationale: Psychoactive substances alter CNS function, affecting motor coordination, cognitive processing speed, and emotional regulation in ways that produce measurable changes in the voice.

Acoustic indicators: Substance use effects on the CNS produce changes in vocal motor control and prosodic patterns, reflected in voice_jitter, voice_shimmer, voice_clarity_hnr, speech_rate, and loudness_mean. Multi-session analysis improves detection of use patterns over time.

Evidence: Multiple peer-reviewed studies on voice as an index of drug effects across substance classes. Not yet validated at clinical prospective scale for Established.

Detects: Potential acoustic changes associated with anemia — reduced aerobic capacity and fatigue effects on vocal energy and effort.

Plausible mechanism: Anemia reduces oxygen-carrying capacity, which can produce fatigue and reduced aerobic endurance. These secondary effects may influence vocal energy and phonatory effort in ways that overlap with the fatigue/malaise acoustic signature. The physiological pathway from oxygen deficit to vocal change is indirect; no voice-specific anemia detection study has been published, and the pathway to a distinct clinical detection model remains to be established through prospective research.

Potential Acoustic Indicators: Fatigue and reduced aerobic capacity may lower vocal effort and sustained phonation, potentially reflected in reduced loudness_mean, increased pause_duration_mean, and changes in speech_rate or voice_clarity_hnr consistent with the fatigue acoustic signature.

Emerging Evidence: Voice and speech as biomarkers for physiological state and fatigue are documented in the literature; acoustic features have been studied in relation to exercise intensity, frailty, and cardiovascular treatment response. The anemia–voice pathway is indirect and would be supported by prospective voice-specific studies in anemic populations.

Detects: Potential acoustic changes associated with dehydration and metabolic volume depletion — vocal fold hydration and mucosal wave properties.

Plausible mechanism: Dehydration affects vocal fold hydration and the properties of the mucosal wave that governs phonation. Reduced systemic hydration decreases the viscosity-reducing properties of the mucus layer on the vocal folds, potentially increasing phonatory effort and altering voice quality in measurable ways. The relationship between oral dryness and voice change is documented in the clinical voice literature; standardized detection models based on voice alone have not yet been published.

Potential Acoustic Indicators: Reduced vocal fold hydration and mucosal wave changes may increase perturbation and phonatory effort, potentially reflected in elevated voice_jitter and voice_shimmer, reduced voice_clarity_hnr, and changes in loudness_mean when sustaining phonation.

Emerging Evidence: Vocal fold hydration and its effect on voice quality are well documented; systematic reviews report that hydration status affects jitter, shimmer, and noise-to-harmonics ratio, and that rehydration can improve these measures. Prospective voice-specific detection models for dehydration or volume depletion have not yet been established.