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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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migrated from Jan 24 '14 at 12:01

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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? – Saaru Lindestøkke 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. – Saaru Lindestøkke Dec 16 '13 at 17:44
Note that even if you fix the problem with your source audio file, your TV may not be able to reproduce such high frequencies, and even if it can, your detector may not be capable/configured-for such high frequencies. Because human hearing is generally considered to end at 20kHz (and what most adults really hear cutting off around 16kHz), most consumer audio gear isn't designed to gracefully handle things above that. – Linuxios Apr 11 at 16:25

As @bart-arondson has mentioned in his comment, you should use PCM wav files to store your audio signal. Be aware that :

  • pure tones close to half the sampling frequency might produce artefacts depending on the technology used by the TV set DAC.
  • TV loudspeakers are not linear at frequencies above 16 kHz (approximately), and your signal might be noticeably attenuated when reproduced in the acoustic domain.
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