Sigma studio for ultrasonic application

Hello ! :)

Im a student in engineering, my project is to develop a directive speaker based on a ultrasonic piezo array. 
The audio signal should be modulated with a sine carrier (AM, DSB). The carrier frequency is around 40khz.
So, I thinking of using sigma studio to do this task. 

My school suggests the use of a PIC18F57Q43 (Which is not a properly DSP, but I can try) 

My questions are: 

  1. Can I use Sigma Studio to code this PIC, (which is not in the list of proposed DSPs), and How? 
    - If not, can I extract the algo from Sigma to implement it into the PiC ? 

  2. If I use a regular DSP like ADAU1701, I saw that the DAC has a limited sampling frequency of 192khz max. Which is a little bit low for my ultrasonic application (40khz output). Is there alternatives DSP références with a higher sampling frequency output ?  (That can be use on Sigma of course)

  3. Last question, is there a way to ‘scope’ the output signal inside Sigma studio software to see the result of my modulation before implement it into DSP ? Or manually scope the signal from a port of my Pc ? 

It’s a lot of question, but your responses could really help me ! 

Thanks you :) 

  • 1) No

    2) I'm not sure why you consider the ADAU1701 sample frequency of 192kHz an issue for 40kHz. Even 80kHz is no problem. Think about it - with 48kHz audio frequencies of 20kHz is no problem, well within Nyquist.

    ps This isn't just theoretical - 40kHz is easily doable at 96kHz sample rate, I've done it. You then get twice as many instructions in as 192kHz. 

    3) Depending on what you're trying to do look at the Simulation Stimuli and Simulation Probe 

  • Thank you for your reply !

    2/ Signal reconstruction remains poor when approaching the Nyquist frequency.
    In practice with a classic signal (20hz-20khz) there are quite a few frequencies close to that Nyquist. The extremely high-pitched sounds of ~20khz are relatively unimportant.
    But in an AM application the signal is only the continuous 40khz sine carrier, rebuilding it is more important I think.
    Reconstructing a 40khz sine with 192khz sample rate means only 4.8 samples points per period, that's not so much.
    However with a good smoothing filter and a tuned LC couple, it can do the trick. To be tested...

    3/ According to my reaserch Simulation Stimuli and Simulation Probe only allow to show the frequency response, not the actual signal (as an oscilloscope can do).
  • 2)You might be right, hopefully someone else will chip in with more practical experience of it than me, however I'd test it before resorting to tuned LC. It works better than you'd think.

    3) You're right. All audio processing is done on the board, not in SigmaStudio - it's not an emulator. You need a board and USBi programmer to test anything with a signal.

    If you want to get an actual signal out of the DSP for testing your best bet is use one or more of the DACs to feed the 'scope from various parts of your virtual 'circuit' mid flow. (I've done this with 40kHz) If the 4 on board isn't enough there's always i2c to add more. 

  • 0
    •  Super User 
    on Apr 7, 2021 9:41 PM in reply to Jon_R

         Hello Jon_R and Maxitechnic,

         SigmaStudio and the ADAU1701 are surprisingly effective for ultrasonic applications.  A college student (majoring in music, not engineering!) designed and built an ultrasonic blind-assist device:

    And there's been various other projects including SSB modulation and demodulation, FM MPX encode and decode, etc.  The limited number of samples per cycle has not prevented these applications.  The DSPs include oversampled brick-wall input filters which resist aliasing, and output reconstruction filters to allow for simple RC filtering at the outputs.  Of course you use a smaller cap than what's shown in the data sheet to support higher output bandwidth.

         Best regards,