Reading an oscilloscope waveform

The X-axis (horizontal) represents time - signals move from left to right. The Y-axis (vertical) represents amplitude - how far the waveform deviates from the centre zero line. Positive values go up (compression), negative values go down (rarefaction). The centre line at zero means silence.

Common waveform shapes

Shape	How it looks	Sound / source
Sine	Smooth S-curve repeating evenly	Pure tone, tuning fork
Square	Abrupt jumps between high and low	Digital signals, buzzer
Sawtooth	Gradual rise then instant drop	String synths, rich harmonics
Triangle	Straight-sided peaks and valleys	Mellow synth sounds
Noise	Completely irregular, no pattern	White/pink noise, hiss
Complex	Jagged, non-repeating	Speech, music, real-world audio

Frequency and period

The period is the time for one complete cycle (one full wave). Frequency in Hz equals 1 ÷ period. A 440 Hz (A4) sine wave completes one cycle in about 2.27 milliseconds. Higher-pitched sounds have shorter periods and denser waveforms on screen.

Privacy

All audio processing happens locally in your browser using the Web Audio API. No audio data is transmitted to any server.

Time/division and volt/division

A real oscilloscope (and this browser simulation) has two fundamental scale settings:

Time/division (horizontal): how many milliseconds or microseconds each grid square represents. A setting of 1 ms/div with 10 horizontal divisions shows 10 ms of signal. To read the period, count how many divisions one complete cycle spans, then multiply by time/div.
Volt/division (vertical): how many volts each grid square represents. With 2 V/div, a waveform spanning 3 divisions peak-to-peak has an amplitude of 6 V_pp. To read amplitude, count divisions from peak to trough and multiply by volt/div.

These two settings are the most confusing aspects for beginners. Adjusting them is how you "zoom in" on either the time or amplitude axis.

Lissajous figures

When an oscilloscope is switched to X/Y mode (one signal on each axis instead of time on the horizontal axis), the resulting figure reveals the frequency ratio and phase relationship between the two signals. These are called Lissajous figures.

Same frequency, 0° phase: a straight diagonal line.
Same frequency, 90° phase: a perfect circle.
Same frequency, other phases: an ellipse whose tilt angle indicates the phase difference.
2:1 frequency ratio: a figure-8 or parabola shape.

Lissajous figures were historically used to tune oscillators to exact frequency ratios before digital frequency counters existed.

Triggering

Without triggering, a continuous waveform would scroll across the screen and appear to move rather than hold still. The trigger circuit waits for the signal to cross a threshold voltage in a specific direction (rising or falling edge) before starting each screen sweep. This ensures the display always starts at the same point in the waveform cycle, making the pattern appear stable.

In this browser implementation, the Web Audio API's AnalyserNode provides FFT and time-domain data. A software trigger scans the audio buffer for a rising zero-crossing (or threshold crossing) to align successive frames, replicating the behavior of a real oscilloscope's edge trigger.