questions about XMOS MCU and ultrasonic digital microphone

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questions about XMOS MCU and ultrasonic digital microphone

Postby mateusmcampos » Thu Feb 08, 2018 2:00 pm

Hello everyone

I am an engineering student and I am working on a project of a microphone array. The digital microphones are Knowles SPH0641LU4H-1 that work in an ultrasonic range, to up 80 kHz.
I intend to use XMOS MCU to process the information this array: PDM to PCM converter; Filtering; delays; sums; beamforming; etc; but in the ultrasonic range.

Would I like to know if it would be possible to use the microphone array library in frequency ranges to up 80 kHz? Or this library is limited to up audio frequency?
If it does not work
Would it be easy to change this library or to develop a library to work in ultrasonic range?
Does it exist a library that it does it? Alternatively, are there resource in XMOS MCUs to use in my project?
Are XMOS MCUs good options for my project?
What is the best development kit to start?

I’m a beginner in XMOS MCUs and I would like your opinion about.

Thank you in advance.
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Postby andrew » Fri Feb 16, 2018 9:12 am

The library has an intermediate format of 384kHz which is accessible over channels. This format is not normally ideal as it contains a lot of alias noise. Alternatively the library can output at 96kHz but you will not get up to 80kHz. You do have the option of taking the 384kHz signal and decimating it to say 96kHz and you would get the control the filtering in this case to suit your needs.

The Xcore is an ideal chip for working with ultrasonics in my biased opinion as we have already tried it successfully.

Be aware that the modulator noise at 80kHz of an PDM microphones is very high. This: ... _Audio.pdf
contains a good graph of how the noise shaping effects the SNR at ultrasonic frequencies.

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