Spectrogram Analysis and Vowel Formants in Praat Tutorial

Acoustic phonetics is one of three interconnected branches of phonetics, alongside articulatory phonetics (production) and auditory phonetics (perception). A complete description of speech sounds requires understanding all three aspects together. Sound waves have three fundamental properties: time (x-axis), amplitude (maximum deviation from rest position, y-axis), and frequency (number of cycles per second). One complete cycle represents the wavelength. Sound production requires two essential preconditions: a source of energy/disturbance and a medium for transmission. In speech, the larynx serves as the primary source through vocal cord vibration, creating phonated airstream that travels through the oropharyngeal chamber. Sound waves are classified as periodic (regular, repeating patterns at consistent intervals) or aperiodic (irregular, changing unpredictably). When multiple periodic sine waves combine, the resulting wave remains periodic with a frequency equal to the highest common denominator of its constituents. From an auditory perspective, periodic waves are perceived as musical and pleasant, while aperiodic waves are considered non-musical or noise.

Acoustic phonetics is the study of the physical properties of speech sounds, focusing on wave characteristics including frequency (measured in hertz, representing cycles per second) and amplitude (maximum displacement from the starting point). Speech waves travel through a propagation medium, typically air, and can be classified as periodic (regular waves produced by vowels and sonorants) or aperiodic (irregular waves produced by obstruents like stops, plosives, fricatives, and affricates). The normal audible frequency range for humans spans 20 to 20,000 vibrations per second, with higher frequencies corresponding to higher pitch.

Periodic sounds (vowels and voiced consonants) have repeating wave patterns allowing frequency measurement, while aperiodic sounds (voiceless consonants and fricatives) have irregular, non-repeating waveforms. This distinction is visible in oscillograms - periodic sounds show regular repeating waveforms, aperiodic sounds show irregular, chaotic waveforms. Vowels produce periodic waves with varying amplitude - 'a' typically has the largest amplitude, 'i' has smaller amplitude, and nasal vowels have even smaller amplitude due to sound energy escaping through the nose. Consonants have different waveform characteristics: stops (p, t, k) show silence followed by sudden energy bursts (explosions), fricatives (s, f) show irregular aperiodic waveforms from turbulent airflow, and nasal consonants show reduced amplitude. Glottal stops produce aperiodic sounds because vocal cords close completely, blocking airflow and creating turbulence without regular periodicity. These acoustic characteristics allow phonetic analysis of speech sounds through waveform examination.

This section explains the fundamental nature of sound waves. Sound is defined as any perturbation of air capable of stimulating the human auditory apparatus. The instructor distinguishes between periodic waves (regular, repetitive waves with consistent format like tuning fork sounds) and aperiodic waves (irregular waves without consistent repetition). Simple periodic waves have a single wave pattern that increases and decreases proportionally, while complex periodic waves consist of multiple overlapping periodic waves that combine to form a single complex wave. Consonants are characterized by aperiodic waves where patterns do not repeat regularly, often involving a mixture of periodic and aperiodic patterns.

Acoustic phonetics studies the physical properties of speech sounds, including time (period for one complete wave cycle), frequency (cycles per second, inversely related to time), amplitude (maximum displacement from equilibrium), velocity of sound (330 m/s in air, varies by medium), wavelength (distance between successive compressions or rarefactions, inversely related to frequency), and pitch (perceived highness/lowness determined by frequency). Sound waves are classified as mechanical (requiring a medium) or electromagnetic (not requiring a medium), and further as transverse (perpendicular particle motion) or longitudinal (parallel particle motion). Waveforms can be simple (single frequency) or complex (multiple frequencies), periodic (repeating patterns) or aperiodic (no pattern, perceived as noise), and continuous or transient (sudden fluctuations). These properties are analyzed using software like Praat, which generates waveforms (amplitude vs. time) and spectrograms (frequency, time, and acoustic energy concentration).

Formants are standing waves within the vocal tract that interact with harmonics, amplifying or reducing their intensity. Five primary formants (F1-F5) are essential for speech: F1 and F2 control vowel production through mandibular opening and tongue position; F3 and F4 form a cluster controlled by pharyngeal and laryngeal movements affecting voice projection; F5 appears above 5000 Hz when the epiglottis contracts. These formants are not absolute values but vary within frequency ranges, enabling the production of different vowels and speech characteristics through vocal tract shape modification.

Formants are the resonant frequencies of vocal tract cavities. As articulatory organs move, cavity shapes and volumes change, altering their natural frequencies. Each cavity has its own resonant frequency at which it amplifies incoming signals. These changing resonances create the formant patterns that distinguish different vowels. Formants appear on spectrograms as thick black bands superimposed on overtones, representing the frequencies amplified by the vocal tract.

Formants are resonant frequencies of the vocal tract that shape voice timbre. They are determined by the physical dimensions of the vocal tract, including the pharynx, mouth, and nasal passages. Different vowel sounds are produced by changing the vocal tract shape, which changes formant frequencies. The human voice produces sounds across a wide frequency range (80 Hz to over 1000 Hz), with the vocal tract acting as a resonator that amplifies certain frequencies while attenuating others.

Vocal formants are the resonance frequencies of the vocal tract that can be adjusted by changing the position and shape of articulators like the tongue, jaw, and lips, while harmonics are the frequencies produced by vocal fold vibration; when formants align with harmonics through resonance tuning, singers achieve greater vocal power, improved intelligibility, and richer resonance.

Formants are resonant frequencies that color sound produced by vocal cords, filtering fundamental frequency to create characteristic timbre. The vocal tract (larynx, oral cavity, nasal cavity) acts as a resonator emphasizing certain frequencies while attenuating others. Different vocal tract lengths and shapes produce different formant patterns, making each voice unique. Famous singers like Pavarotti had distinctive formant patterns enabling effective projection. Formants are measured as F1, F2, and F3, representing first, second, and third resonant frequencies. The brain analyzes these formants to recognize characteristic sounds of instruments or voices.

Praat is a widely-used software for speech and sound acoustics analysis across Linguistics, Phonetics, Hearing Sciences, Music Science, Psychology, and Computer Science. Students must download it from pr.org, selecting their operating system. Audio files for exercises are available in the course Canvas portal under the 'Pro' folder, and should be downloaded simultaneously using Shift-click selection. Sound files open through drag-and-drop or Control+O navigation. The Object List displays opened sounds as temporary copies. The View and Edit button reveals the waveform (raw pressure deviations over time) and spectrogram (frequency content over time). Time information appears with three decimal places for millisecond precision. Clicking and dragging creates selection boxes displaying start time, end time, and duration. Periodic signals like vowels show equally spaced vertical stripes in the waveform, representing repeated glottal cycles. The fundamental frequency equals the reciprocal of the period duration—for a 7.5ms period, this is approximately 133 Hz. Pitch represents the rate of repetition in periodic signals, displayed as a contour showing fundamental frequency over time. Pitch range settings should match the speaker's actual range (typically 70-200 Hz for adult males) for optimal visualization.

Praat is a free speech analysis software downloadable from Google, available for Windows and Mac. After installation, users access two main windows: a display window (which can be closed) and a 'Praat objects' window for file management. Files are opened via 'Open' > 'Read from file'. Spectrograms are viewed by selecting sounds and choosing 'View & Edit', displaying time horizontally and frequency vertically with intensity shown through color gradients. Zooming is achieved by selecting regions and pressing Ctrl+N. Plosive releases appear as vertical bars in spectrograms, with white spaces indicating complete closures before release.

To open audio files in Praat for acoustic analysis, click the 'Read' menu and select 'Read from file' (or use Command+O/Ctrl+O), navigate to your desired file, and select it; the file will appear in the Objects window where you can highlight it to play or analyze it, and you can select multiple files by holding the Shift key while clicking.

Praat is a software tool for acoustic measurements that requires understanding its basic interface operations. Files can be opened by clicking them directly (opening in default audio player) or forcing them to open in Praat through right-click menu options. Once opened, files appear as numbered entries in the Objects list with their type and filename. To view sounds, select the object and click View & Edit. The interface provides essential playback controls: three bars at the bottom allow playing up to a selected point, after a selected point, or the entire sound. This foundation enables users to navigate Praat's core functionality for acoustic analysis.