Tone Generator

Four waveforms, and why they sound different

All four are at the same frequency, so all four are the same pitch. What differs is the harmonic content, and that is what you hear as tone colour.

• Sine — the fundamental alone, with no harmonics at all. The purest tone there is, and the one to use for testing, because anything else you hear is being added by your equipment.
• Square — the fundamental plus every odd harmonic. Hollow and buzzy; the sound of early video game music.
• Triangle — odd harmonics again, but falling away much faster. Softer than a square, closer to a flute.
• Sawtooth — every harmonic, odd and even. The brightest and richest of the four, and the classic starting point for synthesised string and brass sounds.

Frequencies worth knowing

• 20–60 Hz — deep bass, felt as much as heard. Laptop and phone speakers reproduce essentially none of it, so silence here is the speaker, not you.
• 440 Hz — the A that orchestras tune to.
• 1 kHz — the standard reference tone for audio measurement, and near the peak of human sensitivity.
• 2–5 kHz — where the ear is most sensitive, and where speech intelligibility lives. A small boost here sounds much louder than the same boost elsewhere.
• Above 15 kHz — audible to the young, and often not reproduced by small speakers anyway.

Equal loudness is not equal level

Play 1 kHz and then 50 Hz at the same volume setting and the bass will sound much quieter, even though the signal level is identical. Human hearing is far less sensitive at the extremes, and the effect is stronger at low listening volumes.

This is why music sounds thin at low volume and full when turned up, and why hi-fi amplifiers used to have a "loudness" button that boosted the bass at quiet settings.

Common uses

• Testing speakers and headphones — sweep the frequency and listen for buzzes, rattles or a channel dropping out.
• Checking stereo wiring with the channel slider.
• Tuning by ear against a known pitch.
• Testing a room — low tones reveal standing waves where the level changes dramatically as you walk around.
• Hearing what a waveform sounds like, which is worth more than reading about harmonics.

Start quiet. A continuous tone is more fatiguing than music at the same level, and sustained loud tones can damage hearing permanently.

Questions people ask

What is the difference between the waveforms?

The harmonics. Sine has none, square and triangle have odd harmonics, sawtooth has all of them. Same pitch, different tone colour.

Why can I not hear the low frequencies?

Small speakers reproduce almost nothing below about 200 Hz. That is the speaker, not your hearing.

Why does bass sound quieter at the same volume?

Human hearing is much less sensitive at the frequency extremes, and more so at low listening levels. It is why music sounds thin when played quietly.

What is 1 kHz used for?

It is the standard reference tone for audio measurement, and sits near the peak of human sensitivity.