A frequency generator makes one thing: a tone at exactly the pitch you ask for. That sounds like a tool for nobody. It's actually a tool for a surprising crowd — audio tinkerers, teachers, people with ringing ears, and the occasional person trying to chase a raccoon off a porch (we'll get to why that last one flops).
Hardware versions sit on electronics benches and cost real money. The browser version costs nothing and covers most of the same jobs, because a phone's audio output is honestly pretty good between 40 Hz and 18 kHz. Here's what people do with one.
This is the big one. A speaker's spec sheet says "20 Hz – 20 kHz" the way a dating profile says "loves hiking." The claim is aspirational. Feed the speaker a 40 Hz tone and listen: a real subwoofer produces a chest-pressure note, while a laptop produces a sad clicking noise and, somewhere, a marketing department feels a twinge of guilt.
With a generator you can walk the whole range — bass extension at the bottom, treble rolloff at the top, and rattles in between. Sweep mode does it hands-free. There's a full step-by-step guide in this notebook.
People with ringing ears often want to know which frequency the ring lives at. Audiologists do this properly; a tone generator gets you a decent first estimate at home. Slide until the tone seems to melt into the ringing — most people land somewhere between 4 and 8 kHz. That number is useful to bring to an appointment, and some sound-therapy approaches are built around it.
Not medical advice, obviously. A tone generator can describe your tinnitus. It can't treat it, whatever a YouTube title implied.
Start at 8 kHz and climb. Wherever the tone vanishes for you is your ceiling — around 15–17 kHz for most adults, higher for teenagers, lower after every loud concert you ever attended. It's a fun and mildly humbling party trick.
One catch. If the tone "disappears" at 18 kHz, was that your ears or your speaker giving up? You genuinely can't tell by listening — which is why the generator has a built-in speaker check that uses your mic to verify the tone physically exists in the room. Run it before drawing conclusions about your ears.
Physics teachers use tone pairs to demonstrate beats and interference — two tones a few hertz apart make a wobble everyone in the room can hear. Musicians pull up 440 Hz to check tuning against a known reference. Audio engineers use 1 kHz as the standard alignment tone. And 60 Hz is handy for a strange little diagnostic: if a hum in your recording matches a 60 Hz tone (50 Hz in Europe), you've found mains interference, not a bad microphone.
People also use low frequencies to hunt rattles in cars and room resonances behind bookshelves. Play a slow bass sweep and listen for what buzzes along. Something always buzzes along.
The internet loves the idea that a 20 kHz tone repels mice, mosquitoes, raccoons, or teenagers' younger siblings. The controlled studies are consistently unimpressed — pests habituate within days, if the sound bothers them at all. And a phone speaker barely produces those frequencies to begin with, at any useful volume. If ultrasonic repellents worked, pest control companies would be selling tones, not traps.
The "mosquito tone" for humans is the one exception, sort of: a 17.5 kHz tone genuinely is audible to most teenagers and genuinely isn't to most people over 30. Whether that counts as a use or a prank depends on which side of 30 you're on.