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  1. Memory allocators are allowed to break the rules...

    Memory allocators are allowed to break the rules as the objects are not "live" when they are in freelists (one hopes!)
    In a full-blown garbage collector you normally have to completely subvert any...
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    The analog pins for the T4.1 are 14--27 and 38-41...

    The analog pins for the T4.1 are 14--27 and 38-41 according to the info card with the pinouts. You are using
    pin 11 which is digital only.
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    You're results from peak1.read() are spurious...

    You're results from peak1.read() are spurious unless you first check peak1.available().

    I've had a play with the example and I see only zeroes coming out - this is likely EMI on the rails...
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    That tool is only a convenience and is not...

    That tool is only a convenience and is not required at all to build Audio lib programs. Find one of the example programs for the
    Audio library such as...
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    You never release the other blocks, so that upto...

    You never release the other blocks, so that upto 15 old blocks may be stuck in the inputQueue, so that when the inSource
    changes an ancient block will be picked up from one of the stuck channel. ...
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    No need to plug anything in, just configure the...

    No need to plug anything in, just configure the i2s1 output object (it will flap the I2S pins (MCLK1/BCLK1/LRCLK1/OUT1A) so you can't use them for anything else)
    You just need something that's...
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    AudioAnalyzePeak can do this I think.

    AudioAnalyzePeak can do this I think.
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    You've seen and absorbed these resources? ...

    You've seen and absorbed these resources?

    https://www.pjrc.com/teensy/td_libs_Audio.html
    https://www.pjrc.com/teensy/gui/
    https://www.pjrc.com/store/teensy3_audio.html
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    Yes, pull request #390 is already in the system...

    Yes, pull request #390 is already in the system to fix this in the next release. The latest Audio lib repo already has this - the
    warnings are benign.
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    If the digital stream is not stuttering and is...

    If the digital stream is not stuttering and is all zeros, what remains can only be noise on the supply rail getting into
    the analog output. This noise will be pattern sensitive and could...
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    If all the output mixer gains are set to zero...

    If all the output mixer gains are set to zero there should be silence. If not perhaps there is a shortage of Audio buffers or CPU time?
    The ladder filter is expensive in CPU time as it has to do...
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    The datasheet for the WM8731 says nothing at all...

    The datasheet for the WM8731 says nothing at all about any limit on the audio outputs, nor about short-circuit
    protection, about the only clue is that the internal output drivers are portrayed as...
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    T4 support for ADC input was unfinished I...

    T4 support for ADC input was unfinished I believe, I'm pretty sure this has been addressed for uncoming release
    though, but can't find the thread about it. You can probably fix this by adding an...
  14. This immediately suggests rail bounce (inductance...

    This immediately suggests rail bounce (inductance of the wiring causing a spike or ringing on sudden current changes)

    There should be decoupling at both ends of a power cable to quell this...
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    It will depend when the PWM is enabled w.r.t. the...

    It will depend when the PWM is enabled w.r.t. the clock driving the PWM unit I think - the way PWM units work is that the output
    change is triggered by exact matches of the counter register to the...
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    It means add. I've heard this terminology...

    It means add. I've heard this terminology especially when discussing oscillograms
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    Adding DC to the headphone out isn't advised,...

    Adding DC to the headphone out isn't advised, it'll risk pushing the transducer cone to the end-stops.

    Why do you need to detect the difference? Is it to set different levels or some such? Or to...
  18. There's a fix pending to the dynamic update stuff...

    There's a fix pending to the dynamic update stuff I believe, I suggest follow this thread for updates, or to
    try the patch directly:...
  19. And resampling is not trivial processing either -...

    And resampling is not trivial processing either - resample offline if possible.
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    Or even replace the while loop: while (p)...

    Or even replace the while loop:


    while (p) {
    if (p == this) {
    if (p->next_dest) {
    p = next_dest;
    break;
    } else {
    p = NULL;
  21. No pointers in that code, just an array of...

    No pointers in that code, just an array of objects. If pointers were involved you'd replace '.' by '->'
    (or is that what you've done?)
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    The MCP23017 datasheet says it supports 100kHz,...

    The MCP23017 datasheet says it supports 100kHz, 400kHz and 1.7MHz I2C, and has a section on timing requirements for each mode - that
    probably explains why 1MHz is problematic.
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    The Teensy 4 chip isn't rated for more than a few...

    The Teensy 4 chip isn't rated for more than a few mA per pin, I think you are just overloading it.

    However I've had a look at the Vishay datasheet for the 6N137 - you should be feeding it between...
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    24 bit filter coefficients, or 24 bit bit audio...

    24 bit filter coefficients, or 24 bit bit audio or both?
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    Its called MIDI because you just named it as...

    Its called MIDI because you just named it as such. MIDI_CREATE_INSTANCE is a macro that defines an instance
    with the name you give it (last argument to the macro).
  26. pdm input and i2s output ? Have you seen the...

    pdm input and i2s output ? Have you seen the audio lib design tool: https://www.pjrc.com/teensy/gui/
  27. If you are lucky the current was limited enough...

    If you are lucky the current was limited enough not to damage the protection diodes on the chip. 10k is
    a fairly large value and limits the current to 1.7/10k = 170uA.
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    Definitely rather noisy, dynamic mics are low...

    Definitely rather noisy, dynamic mics are low impedance and a good mic preamp is needed to get a good
    noise figure - otherwise there's little point moving to a professional microphone in the first...
  29. 34 and 35 are on the unpopulated microSD pads...

    34 and 35 are on the unpopulated microSD pads (light blue section - they are silk-screened with the light blue names).
    MISO1 is not brought out AFAICT - not every pin can be brought out on the T4.0
  30. There should be a definite noise reduction if...

    There should be a definite noise reduction if using a separate, linearly regulated, analog supply on any ADC or DAC for audio -
    digital supplies for a high speed CPU are typically attrociously noisy...
  31. Just have the pinout cards to hand, like I have! ...

    Just have the pinout cards to hand, like I have! Glad its flying now..
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    You will be seeing the battery voltage droop...

    You will be seeing the battery voltage droop under load - SDcards are very spiky loads as the internal erase cycles are
    heavy current users (there's a whole boost converter being run on the silicon...
  33. [ BTW I think what you have isn't technically a...

    [ BTW I think what you have isn't technically a network analyzer, as you are not measuring reflected power(?) - what you have is
    equivalent to a spectrum analyzer with tracking generator, only...
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    Set pin SS as an output - the Teensy SPI lib...

    Set pin SS as an output - the Teensy SPI lib doesn't do this for you. Look under "Basic Usage" here:
    https://www.pjrc.com/teensy/td_libs_SPI.html
  35. Pins 7 & 8 on the T4 are RX2/TX2, and are also...

    Pins 7 & 8 on the T4 are RX2/TX2, and are also I2S pins. Are you using either of these? On the T3.2
    RX2/TX2 are on different pins...
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    The way "thru" works in such devices is using...

    The way "thru" works in such devices is using software I think, since the use of the output port has to be shared
    between local output packets and "thru" packets without mangling either. I think...
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    BJTs are typically slower than MOSFETs if the...

    BJTs are typically slower than MOSFETs if the MOSFET is driven with enough current - however a
    large MOSFET can have a lot of capacitance and need quite high currents to switch fast - so it
    very...
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    If you do some testing you'll find they are...

    If you do some testing you'll find they are simply not reliable enough, fortunately, as a ceiling fire in a public space is about the
    worst-case scenario there is - you do not want to go there,...
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    Then you have no headroom for a regulator. I'd...

    Then you have no headroom for a regulator. I'd suggest separate supplies for Teensy and amp in that case.
    Digital and analog audio don't mix well as even a few mV of digital hash can be highly...
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    A low drop out linear regulator capable of the...

    A low drop out linear regulator capable of the current and with a suitable voltage. There are 1000's - I am not a search engine!
    Digikey/Mouser/Farnel - they have search facilities.... What battery...
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    As I said use a separate linear regulator for a...

    As I said use a separate linear regulator for a quiet supply - this means you need enough voltage headroom in the first place.

    You may still have the issue that the source isn't clean - do you...
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    Ah, the TDA2822 has only 24--30dB of PSRR, so it...

    Ah, the TDA2822 has only 24--30dB of PSRR, so it definitely needs a linear voltage regulator all to itself to be "quiet"...
    Even the PAM8403 class D chip does a lot better than that (59dB PSRR)
  43. The FFT utilizes a factorization of the DFT...

    The FFT utilizes a factorization of the DFT matrix and divide-and-conquer to calculate the DFT more efficiently,
    its just algebraic simplification at heart.
    Its common, but not necessary, to...
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    I can't see a reference design - the datasheet...

    I can't see a reference design - the datasheet does explain about noise-reducing components on the digital signals,
    but you seem to have used 100nF for a noise-reducing capacitor value which is far...
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    Can't find a datasheet for the TDA1822 - is that...

    Can't find a datasheet for the TDA1822 - is that the correct part number? what sort of amp is it?
  46. In the arm_cfft_radix4_q16 call, part of the...

    In the arm_cfft_radix4_q16 call, part of the CMSIS library provided by ARM:


    arm_cfft_radix4_q15(&fft_inst, buffer);

    You can look up the docs for these arm routines by googling the function...
  47. Or is shorted, or lacks proper pull-up resistor -...

    Or is shorted, or lacks proper pull-up resistor - I suggest using a multimeter and turning the encoder very slowly to check the
    voltages are changing as expected on either signal.
  48. That's odd as processor usage should be...

    That's odd as processor usage should be independent of memory use really?!
  49. Thread: ADXL mm/s

    by MarkT
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    First an accelerometer gives acceleration...

    First an accelerometer gives acceleration readings, m/s^2, not m/s

    Secondly magnitude _is_ amplitude (without the phase).

    To calculate totals you have to add magnitude-squared, which is...
  50. Ditto AudioProcessorUsage and...

    Ditto AudioProcessorUsage and AudioProcessorUsageMax() then. If the processing is taking 100% of the CPU, same
    problem...
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