Pure tone/Complex tone
Sound is classified to pure tone or complex tone. Pure tone is theoretically existing, but naturally sound contains infinite pure tones, so called complex tone.
But in the sound science world we assume pure tone as a fundamental of sound and construct theories on it.
Pure tone :
The shape of pure tone is described as "sine wave", having only 1 particular frequency. Therefore it is called "pure tone".
Complex tone :
There are no pure tones in the natural world. More than 1 (to infinite) frequency is mixed in a natural sound, which is called "complex tones".
Tool : iPhone 11
App : Sonic Tools SVM
Sonic Tool SVM has a Sound-Spectrum-Monitor and a Oscillator which can be set any number from 20(min) to 22,050(max). The range is almost the same as Hz which can be audible for humans in theory.
Therefore in thr experiment I set some numbers of Hz on Oscillator, and heard if they were audible or not then watched the change of highest power spectrums, which were shown center-top of the Sound-Spectrum-Monitor.
Oscillator of "Sonic Tools SVM"
In cases of oscillator setting less than 100Hz, spectrum-monitor could not show the same Hz as the highest power spectrum. It is because low tones generated by the oscillator were erased by other natural tones, such as the sound of the air conditioner which was moving in my room.
Result :audible but the the number of Hz shown on monitor was not stable to show the number around 100Hz. It was changeable among the range of 50-115.
(Screen shot of Sound-Spectrum-Monitor)
Result :audible, but weak.
Result :audible, prominent power spectrums around 500Hz were seen.
Set :1,000Hz (1K)
Result :audible, prominent power spectrums around 1,000Hz were seen.
Set :2,000Hz (2K)
Result : audible, prominent power spectrums around 2,000Hz were seen.
Set :5,000Hz (5K)
Result :audible, prominent power spectrums around 5,000Hz were seen.
Set :10,000Hz (10K)
Result :audible, prominent power spectrums around 10,000Hz were seen.
Set :20,000Hz (20K)
Result :NOT audible. The tone generated by the oscillator was not audible for me. And other tones are much larger than 20K's power spectrum. So, the monitor showed 24Hz as the highest tone. If in an anechoic room shutting up any noises, it can be audible.
But on the other hand Spectrum-Monitor was obviously picked up 20K pure tone by the microphone of the iPhone.
As a result of experiment using the iPhone App, we could visualize power spectrums in nature. Theoretically pure tone exists, but in reality complex tone is dominant.
Compact Disk (CD) operates 44.1kHz. And humans' upper audible range is around 20kHz. I am not sure high resolution sound is necessary for us... I would like to study sound science furthermore and enhance the joy of sound.