超声波 iPhone（Shopkick 信号技术）
我认为shopkick正在检测人耳听不到的非常高频信号。但真正的问题是他们如何检测iphone中超过22khz的信号。我检查过iphone麦克风的频率响应，似乎在人类可听范围内的20赫兹到22赫兹。
http://blog.faberacoustical.com/2009/iphone/ iphone-microphone-Frequency-response-comparison/ http://www.businessinsider.com/shopkick-crate-barrel-2010-12?op=1
你可以吗在这方面指导我。如果可以使用 iPhone 麦克风，那么我们可以进行一些信号处理，特别是 FFT 以获得频率。
I think shopkick is detecting very high frequency signal which is not audible to human ear.But the real question is how they can detect signal of more than 22khz in iphone. I have checked frequency response of iphone mic,it seems to be from 20 hz to 22 khz within the human audible range.
http://blog.faberacoustical.com/2009/iphone/iphone-microphone-frequency-response-comparison/ http://www.businessinsider.com/shopkick-crate-barrel-2010-12?op=1
Can you guide me on this. If it is possible with iphone mic,then we can able do some signal processing specifically FFT in order to get frequency.
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嗯，我目前正在开发一个类似的系统，使用这些高频传输数据，这就是我发现的。请记住，我是用 Android 手机（主要是 Galaxy S 系列）进行此操作。
首先，20khz 到 22khz 的频谱似乎很有前途，因为我们测试的所有手机都可以检测到它，甚至其中一些手机可以重现它。这些频率对于任何年龄段的人类来说都是听不到的，甚至狗和猫似乎也没有注意到它们。如果您的目标是（实际上避免）人类检测，您甚至可以低至 18khz，因为大多数人不会听到这个声音。这为您提供了 4000hz 的带宽，您可以将数据频率调制到其中。当然不要指望传输8mp图像，但可以传输一些小数据。你是对的，你可以使用 FFT 转换到频域并分析这些频率，这甚至可以在 Java 中的旧手机上完成（我认为在 Objective C 中这样做会更快）。
此外，如果您的 iPhone 数量很少，您可以安装任何频率分析仪，并在另一台 iPhone 或某些扬声器上播放您想要的频率，以测试它们可以检测到的内容。请记住，标准桌面扬声器可能能够播放给定的频率，但会引入较低频率的噪音。压电高音扬声器可能最适合这些类型的声音，但我必须说我正在使用 iPhone 4 来播放这些频率以有效地测试队列。
我在某处读到，Shopkick 现在甚至可以通过商店 PA-s 播放声音代码，并且由于这些扬声器并未真正针对 20khz 以上的响应进行优化，我也开始怀疑他们使用低于该频率的频率。查看此网站，了解一些人用来欺骗系统的不同商店代码 http://www.ceploitips.com/2011/03/shopkick-walk-in-files.html
请记住，使用这些可能会禁止您的帐户，因为它们改进了滥用检测算法。
另外，我也想了解有关 Shopkick 实施的更多信息，因此如果有人查看此内容，请分享一些链接。
Well I am currently working on a similar system of transmitting data using these high frequencies and this is what I found out. Al-thou keep in mind that I am doing this with Android phones, mostly Galaxy S line.
First of all spectrum of 20khz to 22khz seems quite promising because it can be detected by all phones we tested and even reproduced by some of them. These frequencies are inaudible to humans of any age and even the dogs and cats seem to not notice them. If you are targeting (actually avoiding) detection by humans you could even go to as low as 18khz since most people wouldn't hear that. This gives you a bandwidth of 4000hz which you can Frequency modulate a data into. Of course don't expect to transmit 8mp images but some small data can be transmitted. You are right in the part that you could than use FFT to transit into frequency domain and analyse those frequencies, this can be done even on older phones in Java (I think doing it in objective c would be even faster).
Also if you have few iPhones on your disposal you could install any frequency analyser and play the frequencies you want on another iPhone or some speaker to test what they can detect. Just keep in mind that standard desktop speakers would probably be able to play the given frequencies but will introduce noise of lower frequency. Piezo tweeters are probably best for these type of sounds al-thou I must say I am using iPhone 4 to play these frequencies for testing quete efficiently.
I read somewhere that Shopkick now even plays there sound codes over stores PA-s and since those speakers are not really optimised for above 20khz response I too am starting to suspect they are using frequencies below that. Take a look at this website for different store codes that some people are using to cheat the system http://www.ceploitips.com/2011/03/shopkick-walk-in-files.html
Keep in mind that using these might ban your account since they improved there misuse detection algorithms.
Also I too would like to read more about the Shopkick implementation so if anyone viewing this has some link please share.
首先，人类的听力在 20 KHz 时几乎达到顶峰，即便如此，也需要非常年轻的人类以及沿着这些较高频率的非常低且不稳定的转变。例如，我可以在 iPad 最大音量下以 48 KHz 的采样率发出低至 18 KHz 的音调，甚至我的狗都不会注意到。阅读心理声学，您会发现人类甚至会过滤频率非常低的回声，但我们不会注意到它们。
但就 ShopKick 而言，我认为它们甚至不会超过 21 KHz。我在 iPhone 上创建了几种数字音频调制，21 KHz 似乎是任何距离的上限。
如果您对自己正在做的事情提供更多意见，将会有所帮助。我从问题中假设您想要在两个设备之间调制数字信号。
First, human hearing pretty much tops out at 20 KHz and even that requires a very young human and a very low and erratic shift along those upper frequencies. For example, I can produce a tone as low as 18 KHz at full iPad volume at a sample rate of 48 KHz that even my dog doesn't notice. Read up on PsychoAcoustics and you will see that humans filter echoes at even very low frequencies that are there but we don't notice them.
But in the case of ShopKick, I don't think they are going above even 21 KHz. I have created several digital audio modulations on the iPhone and 21 KHz seems to be the upper limit for any distance at all.
It would help if you gave more input on what you are doing. I assume from the question you want to modulate a digital signal between two devices.
我最好的猜测是他们正在使用最大长度序列。这些几乎就像覆盖了大范围音频频谱的微弱背景嘶嘶声。检测的关键是该模式准确重复，并且手机有一个按键，可以通过将按键与传入的音频相关联来检测声音。
My best guess is that they are using maximal length sequences. These are almost like a weak background hiss that covers a large range of the audio spectrum. The key to detection is that the pattern repeats exactly and the phone has a key that detects the sound by correlating the key and the incoming audio.