Acoustic Science & Signal Processing Guide

A Technical Overview of Web Audio API Synthesis, Auditory Neuroscience, and Psychophysiology Stimulus Generation.

1. High-Precision Digital Signal Processing (DSP)

Rumbling utilizes the standard W3C Web Audio API to generate high-fidelity audio frequencies directly inside your web browser. Rather than playing recorded sample buffers, audio waveforms are synthesized continuously in real-time using mathematical oscillator functions operating at high floating-point sample rates (44.1 kHz / 48 kHz).

Sine Wave Synthesis: Produces a pure fundamental frequency without upper harmonic overtones \(y(t) = A \sin(2\pi f t + \phi)\). Essential for audiometry testing and baseline psychoacoustic experiments.
Square & Sawtooth Waves: Contain rich odd and even harmonic spectrums useful for filter testing and synthesizer patch design.
Calibrated Noise Profiles: Generates uniform White Noise (equal energy per Hz), Pink Noise (-3dB/octave slope for human hearing calibration), and Brown Noise (-6dB/octave slope for acoustic masking).

2. Psychophysiology & Auditory EEG Stimulus Paradigms

In cognitive neuroscience and electrophysiology, auditory stimuli are employed to evoke measurable electroencephalographic (EEG) responses in the auditory cortex:

Auditory Steady-State Response (ASSR)

ASSR utilizes 40 Hz amplitude-modulated continuous tones to measure gamma-band neural phase locking in the primary auditory cortex. It is widely used in clinical audiometry, cognitive aging studies, and schizophrenia biomarkers research.

Event-Related Potential (ERP) Oddballs

The Oddball paradigm presents repetitive standard tones (e.g. 1000 Hz at 80% probability) interspersed with pseudo-random target deviant tones (e.g. 1200 Hz at 20% probability) to evoke P300 waves and Mismatch Negativity (MMN) cognitive potentials.

3. Binaural Beats & Brainwave Entrainment

Binaural beats occur when two pure sine tones of slightly differing frequencies are presented separately to each ear via stereo headphones. The superior olivary complex in the brainstem integrates the signals, creating a central beat perception equal to the frequency difference \(\Delta f = |f_{left} - f_{right}|\).

Delta (0.5 – 4 Hz): Deep restorative sleep, unconscious states.
Theta (4 – 8 Hz): Deep relaxation, REM sleep, creative flow states.
Alpha (8 – 13 Hz): Calm alertness, stress reduction, anxiety relief.
Beta (13 – 30 Hz): Active concentration, cognitive focus, alertness.
Gamma (30 – 100 Hz): Peak mental performance, associative memory integration.

4. Uncompressed 16-Bit PCM WAV Export Architecture

Rumbling incorporates an OfflineAudioContext pipeline to render audio signals faster than real-time without hardware DAC distortion. Audio buffers are formatted into standard 16-bit uncompressed PCM stereo WAV files compliant with RIFF specification standards. These high-precision files can be imported directly into acoustic analysis software (e.g., Praat, MATLAB, LabVIEW, PsychoPy) or DAW workstations.