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  1. My point was that the ADS1115 is inherently...

    My point was that the ADS1115 is inherently integrating over its long sample period, so will have relatively little issue
    with wideband noise at the input.

    If you want a fast >=16 bit ADC, the...
  2. The recommendation from TI seems to be direct...

    The recommendation from TI seems to be direct grounding at host end, ferrite beads to groundplane at client end. https://www.ti.com/sc/docs/apps/msp/intrface/usb/emitest.pdf
  3. The LTC1867 only claims 89dB SNR, which is about...

    The LTC1867 only claims 89dB SNR, which is about 14.5 bits equivalent.
    The ADS1115 claims full 16 bit noise-free at lower rates and not far off 16 bits at the full 860 SPS.

    Couple this with the...
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    Sorry for the delay in replying. Recently been...

    Sorry for the delay in replying. Recently been tidying up some old branches and spotted this.

    Its a bug in the folder, whenever the folder saw a sample value ending in 0x8000 it was glitching.
    ...
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    Ah, those are my PDM changes, I noticed them...

    Ah, those are my PDM changes, I noticed them eventually - I'll have a look at fixing this.

    [ pull request https://github.com/PaulStoffregen/Audio/pull/390 ]
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    As aside about switches - its been briefly...

    As aside about switches - its been briefly mentioned above I think, but hard switching of audio is going to
    produce potentially loud and annoying clicks, since truncating a waveform is equivalent to...
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    8MB? SDcard? No, that's going to take a while I...

    8MB? SDcard? No, that's going to take a while I think.

    You don't want to let that amount of data go without backup anyway, so why not flush it to backing store
    regularly so there's never that...
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    My other thought was a busy-waiting loop would be...

    My other thought was a busy-waiting loop would be entirely in cache and avoid hitting RAM for instruction fetch or any load/stores.
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    Switch-mode power supplies don't need such large...

    Switch-mode power supplies don't need such large capacitors as they can pull power from the waveform
    when its well below peak voltage, and thus don't have to store as much energy as a...
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    The drop in current suggests the processor is...

    The drop in current suggests the processor is halting and waiting for interrupt. Bulk SPI
    operations are probably being DMA'd.
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    Little tip about PCB prototypes - ensure every...

    Little tip about PCB prototypes - ensure every important signal has at least one via not covered by a component -
    these make convenient points to stick a thin wire in for either 'scope/LA probing...
  12. Fig 37.2 in the processor manual shows that the...

    Fig 37.2 in the processor manual shows that the way I2S data inputs and outputs are multiplexed in SAI1
    is:


    function T4 name T4 pin no
    RX0 IN1 8
    TX3 / RX1 OUT1D 6...
  13. Surely you can have a setup with one ADC or DAC...

    Surely you can have a setup with one ADC or DAC as master, and everything else as slave, including Teensy? The clocks are
    routed from the master to everything, which should mean the Teensy can run...
  14. Its probably doing the bass boost by attenuating...

    Its probably doing the bass boost by attenuating the other frequencies - simply up the overall gain with the volume()
    and/or lineOutLevel() methods?
  15. The way I'd do this is populate a lookup table...

    The way I'd do this is populate a lookup table with RGB values indexed by decibel. Then run through the
    FFT bins converting the value to decibels, lookup the pixel colour and write that to the...
  16. Thread: Bat detector

    by MarkT
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    78,349

    Actually LP2950Z took me to a Micrel datasheet...

    Actually LP2950Z took me to a Micrel datasheet which is a 5V only part.

    There is indeed an LP2950-33 from TI. The '50' in the part number strongly suggests 5V too.
  17. Thread: Bat detector

    by MarkT
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    78,349

    The LP2950 is 5V and is the wrong part number on...

    The LP2950 is 5V and is the wrong part number on the schematic as far as I can see - you need a 3.3V output regulator
    in that position or bad things happen. Its not uncommon to see the wrong part...
  18. Thread: FFT on Teesy 4?

    by MarkT
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    Voice spectra contain both the signature of the...

    Voice spectra contain both the signature of the harmonics, related to the waveform from the vocal chords,
    and the filtering envelope imposed by the throat/mouth cavity, which doesn't change in...
  19. AccelStepper was written for slow...

    AccelStepper was written for slow microcontrollers and doesn't have enough delay for the
    pulse generation.

    Try


    void setup()
    {
    stepper.setMinPulseWidth(15);
    ...
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    Well I've experimented with CIC cascades and...

    Well I've experimented with CIC cascades and multi-state decimation and don't seem to get any speed advantage, though
    some space advantage. CIC cascading can be optimized by table lookup it turns...
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    The integer performance of the T4 is about 300...

    The integer performance of the T4 is about 300 times the Uno, the floating point is probably 4 to 5 orders of magnitude
    faster on the T4... And the T4 has enough RAM for typical DSP tasks, the Uno...
  22. Thread: FFT on Teesy 4?

    by MarkT
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    So long as the signal is in the correct voltage...

    So long as the signal is in the correct voltage range, 0..Vcc (otherwise you'll risk frying the chip - the suggested interface circuit in the
    docs for adc input doesn't seem to feature any...
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    Thought I'd pop my RF spectrum analyzer on a PDM...

    Thought I'd pop my RF spectrum analyzer on a PDM signal from one of these microphones to see what sort of
    noise shaping they have - 3 plots zooming in on the audio band, with full-scales of 5MHz,...
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    You might get a better response with the Remez...

    You might get a better response with the Remez algorithm rather than the window method?
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    Can you edit in code tags for those please?

    Can you edit in code tags for those please?
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    Well the $45 seems fairly plausible - here's a...

    Well the $45 seems fairly plausible - here's a competitor: https://uk.farnell.com/mikroelektronika/mikroe-1767/add-on-board-raspyplay4/dp/2521708

    Not sure whats on the $99 board, but a low volume...
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    Well the stopband is about 1/3rd of Nyquist, not...

    Well the stopband is about 1/3rd of Nyquist, not 1/4th... But its about -60dB which is much better.

    BTW I use Python and numpy / scipy.signal / matplotlib.pyplot packages for all my experimenting...
  28. AudioControlSGTL5000 is the audio lib class. ...

    AudioControlSGTL5000 is the audio lib class. These are all documented in the audio lib tool - just click
    on any object on the left hand side for its docs: https://www.pjrc.com/teensy/gui/
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    The normal way to do this is using a headphone...

    The normal way to do this is using a headphone socket with a built in switch, the switch
    opens when the headphone plug is inserted, disconnecting the speaker. A series resistor
    is typically used...
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    From what I can tell from the docs for the...

    From what I can tell from the docs for the interpolation and decimation functions you are doing things right.

    Have you tried without any of your intermediate processing, just interpolation...
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    And another observation I have - I'm not sure the...

    And another observation I have - I'm not sure the PDM code has to be incompatible with I2S output on the same I2S unit, as the
    clocking is the same. I might have a look at making this work, so that...
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    digitalWriteFast is a better tool for raw timing,...

    digitalWriteFast is a better tool for raw timing, less overhead than digitalWrite.
  33. Thread: Teensy Freeze?

    by MarkT
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    The datasheet says operating range 0 -- 95C,...

    The datasheet says operating range 0 -- 95C, storage -40C -- 150C, so yes its not expected to function below 32F, but
    probably ought to survive them. I'd suspect themal stress has lifted a few...
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    Thats a great question - whatever the Adafruit...

    Thats a great question - whatever the Adafruit PDM module uses - they don't seem to say, although theres a
    good bet its the MP34DT01-M as that's referenced in a few places alongside that module,...
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    Well the MAX9880A has a "voice phase delay" spec:...

    Well the MAX9880A has a "voice phase delay" spec: https://datasheets.maximintegrated.com/en/ds/MAX9880A.pdf
    and the PCM1803A has a "group delay time" spec:...
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    BTW it strikes me that on the T4 you could move...

    BTW it strikes me that on the T4 you could move PDM to the secondary I2S pins to avoid conflicting with the audio shield,
    but I'm not sure how to reconfigure all the registers for this. Paul??
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    I have a pull-request for adding T4 support to...

    I have a pull-request for adding T4 support to AudioInputPDM: https://github.com/PaulStoffregen/Audio/pull/387

    You only need to patch one file for testing, input_pdm.cpp

    In the end the existing...
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    I popped a 'scope on the data in and data out as...

    I popped a 'scope on the data in and data out as well as the analog line in and out and measured, for SGTL5000 at 44100SPS a
    delay of about 280Ás for ADC and 240Ás for the DAC, using square wave...
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    Some IMUs do conversion internally to...

    Some IMUs do conversion internally to DCM/quaternion/etc, which is very handy as all the complexity of combining sensors
    is done for you and calibrated... But if you just have bare sensors on an...
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    You'd need buffer amps for each hold cap I think,...

    You'd need buffer amps for each hold cap I think, perhaps a row of quad JFET input or CMOS input opamps, such as MCP6024's
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    AudioAnalyzePeak would do a similar job without...

    AudioAnalyzePeak would do a similar job without extra hardware
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    The time constant of a circuit with resistors and...

    The time constant of a circuit with resistors and capacitance is simply RC. So 10k resistance and 100pF of stray capacitance
    (a very rough guess) would give a rise time around 1Ás. Mechanical time...
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    Ah, I was looking at the Frank B version......

    Ah, I was looking at the Frank B version... whoops.

    This means the PT8211 output class is incompatible with the I2S input class, which seems rather restrictive.
    Also from what I can tell the...
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    Encoding compressed audio is much slower than...

    Encoding compressed audio is much slower than decoding, though the T4 has serious grunt,
    its worth being aware this might be an issue.

    What do you mean by an FPU library? libm?
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    Just looking back over this thread and had a...

    Just looking back over this thread and had a quick look at the PT8211 ds - no oversampling at all, its a
    straight DAC. The datasheet says you can do 8x over-sampling, which simply means its rated...
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    I've been looking at PDM recently. No the audio...

    I've been looking at PDM recently. No the audio library doesn't support T4 for PDM yet (if you look in the sources
    its clearly ifdef'd out for T4. It would need the low level code for configuring...
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    If you going the route of redundancy why not...

    If you going the route of redundancy why not route ground between signals to control crosstalk? you can still double up
    signals like GND/A/A/GND/B/B/GND/....
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    That amp can only do 3.7W into 3 ohm speakers,...

    That amp can only do 3.7W into 3 ohm speakers, it'll be more like 1.5W into 8 ohm - however you could parallel two
    or three 8 ohm speakers to get more from it. It needs the full 5V supply to get...
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    I'd add a caution here: audio DACs and ADCs...

    I'd add a caution here: audio DACs and ADCs typically don't have accurate voltage levels, for instance the gain error on the PCM5102A
    is worst-case +/- 6% (+/- 0.5dB). This would be a show-stopper...
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    Bear in mind voice recognition is not a simple...

    Bear in mind voice recognition is not a simple problem. For instance have a look at this paper as an example of the techniques
    and an idea of the complexity:...
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