iPhone超声检测（超过22千赫） [英] iPhone ultrasound detection (more than 22 kHz)

问题描述

什么是可以在iPhone 3GS和上述检测出的最大频率？我一直在探索iPhone音频。我需要检测22千赫的声音频率，无需任何外部设备。这可能吗？

What is the maximum frequency that can detected in iphone 3GS and above? I have been exploring the iPhone audio frequency. I need to detect sound frequency of 22 kHz without any external device. Is it possible ?

推荐答案

如果microohone设计不好，就会有一个滚降奈奎斯特频率略低于开头的抗混叠滤波器以保证能量高于奈奎斯特是最小的。锋利的奈奎斯特滤波器使得声音响起。因此，如果采样率是44.1，它很可能是奈奎斯特滤波器开始于大约18千赫，22千赫达到大约40分贝以上的衰减。

if the microohone is designed well, it will have an anti-aliasing filter with a roll off beginning slightly below the Nyquist frequency to ensure that energy above the Nyquist is minimal. A sharp Nyquist filter causes ringing of the sound. Thus, if the sampling rate is 44.1, it is likely that the Nyquist filter starts at around 18 kHz, reaching around 40 dB or more attenuation by 22 kHz.

所以我怀疑22千赫是有点太高，如果采样率44.1千赫。但是，如果采样率为48 kHz，那么你可能是幸运的。

So I suspect 22 kHz is a little too high if the sampling rate is 44.1 kHz. However, if the sampling rate is 48 kHz, then you may be lucky.

要纠正先前的帖子，如果没有抗混叠滤波器，你仍然可以检测到的东西奈奎斯特频率以上，但你测量频率将是错误的。

To correct an earlier post, If there is no anti aliasing filter, you can still detect things above the Nyquist frequency, but the frequency you measure will be wrong.

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