Research中采样率，bin,FFT后的理解

读paper：AirLink: Sharing Files Between Multiple Devices Using In-Air Gestures

其中一段中一些数字的理解：

AirLink requires a pilot tone continuously played through the device’s speakers. Most speakers on phones and laptops are able to generate audio up to 22 KHz. In this work we selected the pilot tone at 18.8 KHz because it is usually inaudible for human while detectable by almost all standard microphones. With this ultrasonic tone being emitted, motions near the device cause Doppler-shifted reflections,which can be picked up by the microphones.The system s