Thanks bill.yu for the late answer,
I updated my system with the following commands:
</s>sudo apt-get update<e>
</s>sudo apt-get upgrade<e>
After that, I followed your instructions as you described it, with the following results:
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sudo pip install webrtcvad
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sudo apt-get install portaudio19-dev
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sudo apt-get install python-numpy
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sudo pip install pyaudio
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sudo pip install pyusb
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Nice regards,
Chris