Audio spectrum analyzer
The spectrum analyzer splits what the microphone hears into frequency bands, so you can see which pitches are present rather than only how loud the whole signal is.
| Sensor used | Built-in microphone |
|---|---|
| Unit | Amplitude per frequency band (Hz) |
| Useful range | Bounded by the sample rate; about 20 Hz to 20 kHz at best |
| Cannot do | Calibrated acoustic analysis, or capture ultrasound above the sample-rate limit |
The mechanism, not the marketing.
Audio arrives as a stream of amplitude samples over time. A Fourier transform converts a short window of those samples into the set of frequencies that would combine to produce it, and the display plots the strength of each band.
This makes things visible that a single loudness number hides — a hum at a specific frequency, the harmonics of a musical note, which part of the spectrum a rattle occupies.
What a phone cannot do here.
- The highest frequency that can be represented is half the sample rate. At the common 44.1 kHz that is about 22 kHz, and content above it cannot be captured at all — so ultrasound is out of reach.
- Phone microphones are voice-tuned, so low bass is attenuated and the top end rolls off. The shape of the spectrum reflects the microphone as much as the sound.
- Amplitudes are relative. As with the sound level meter, there is no calibration reference behind the numbers.
Can it detect ultrasound or dog whistles?
Generally no. The sample rate caps the highest measurable frequency near 22 kHz, and phone microphones roll off well before that.
Why do bass frequencies always look weak?
Phone microphones are tuned for speech and physically tiny, so they are much less sensitive at low frequencies than to the mid-range.
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