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FSK Demodulation with ADAU 1701

Category: Software
Product Number: ADAU 1701


I am firmly new to DSP and just verifying, if my application can be fulfilled by ADAU1701. We use this DSP for audio enhancement and signal leveling. Now I am wondering, if it could also demodulate an FSK signal. In this case, we would not need an additional modem IC.

The requirements are really simple: frequency-shift between 1300 Hz and 2100 Hz; Modulation rate of 1200 baud

However, The FSK signal is transmitted along with default speech audio and I need to detect the FSK signal and mute it on one output channel.

I found approach for incoherent filters here. However, I cannot get it to work.

Thanks in  advance.

  • Hello Lama,

    You found the right post with two different ways to demodulate. So you want to mute the audio output when FSK is detected correct? 

    Well, the first approach in the post you found is showing a way to do it. The output of the two filters are going through a peak envelop generator. That output can be summed and tested with a threshold level stored in a DC cell using an ABCD block like KJBob did. Then with that signal you invert it and use that to control a volume control. Most of the pieces are there. 

    So what are you not able to get working? The FSK or the muting?

    Feel free to attach your project. It usually saves time so we are not guessing. 

    Dave T

  • Hello Dave,

    here is my project:

    I am still working on detection. I guess muting will be easy.

    Made some progress, so now I can measure the GPIO 2 and 3 outputs on a logic analyzer. If I play a pure 1300 Hz sine wave tone, GPIO 2 becomes Low Level. On 2100 Hz it becomes high level. When I lower the Level for threshold to 0.02, I see GPIO 2 level too.

    But I am a little bit disturbed by the fact that when I raise the input volume above 30 %, the audio output on the speaker has more and more gaps.

    When I play a pure sine tone of 1300 Hz, I do only have these hickups - no real tone at all.

    However, with my real FSK signal, I detect nothing at all.

  • The gaps come from insufficient Power supply. Sorry for this inconvenience

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