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I am developing an application that will detect a high frequency sound played by TV. My TV is capable of playing mp3, wma and wav files. When I generate a high frequency audio sound file (18 kHz to 21 kHz) whit Audacity. Than convert it to mp3, wma or wav the sound on this frequencies is cut of, so I can't detect it any more.

Can audio files in these formats carry sounds on this high frequencies? If yes, how can i generate them?

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There's a good question in here, but you will need to supply more information to allow people to answer your question. At what sampling rate do you export the audio? How do you check if the frequencies are cut-off? Do you use an oscilloscope? –  Bart Arondson Dec 13 '13 at 11:51
    
Sampling rate is 44100 Hz. I use an iPhone app to get a frequency domain representation of the played signal. No oscilloscope in use. When generating a tone with freq. 20 000 Hz using a live tone generator I can perfectly recognize the frequency of the live tone generator. But with the method explained in the question no signal on that frequency can be detected. So i suspect it is cut-off.. –  Ivo Patrick Tudor Weiss Dec 16 '13 at 13:59
    
I just used SoX to generate a tone of 210000Hz at a sampling rate of 48kHz and could see in the spectral view of Adobe Audition that the .wav file did contain a tone at 21kHz. Doing the same, but outputting to .mp3 showed that the mp3 file did not have a 21kHz tone, but did have some "noise" at lower frequencies. I would suggest you give SoX a try to generate the tone and export it as wav. –  Bart Arondson Dec 16 '13 at 17:44
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