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Thanks Paul! :D

Best of wishes for 2021 to everybody.

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I thought there was another reply... but it seems to be gone :D

Is you hiss as loud as speech at 1 meter? That would equal about 60 to 70 dB. If so, then something is not right. The hiss should be atleast 20dB lower. Or 1/10th of a speech signal at 1 meter.

Next. See what the analog output is of the electret module at your intended SPL. See if you have high enough sensitivity.

IIRC that electret module has a sensitivity adjustment pot.

It might...

Find out if your ADC reads zero-ish with a low values potenter. And find out what the high values at 3.3v too. Might be better to use an lower ADC reference value to ensure that the electret...

The ADC has an effective dynamic range of 13 to 14 bits. That depends on how low you can get the source impedance driving the ADC. So expect at least 4 to 5 bits of random fluctuations rms That’s...

ADAfruit isn't selling garbage. The MAX4466 will get you to 30dBA if used correctly. Long wires dont cause hiss. An opamp with enourmoud bias current like the costly AD797 is a bad choise for a...

The MAX4466 should be able to getdown to 30dBA.. that pretty silent and very suitable to pickup voices from 1 mtr distance, prolly not good enough for distant bird sounds. If you cannt get descent...

These number really depend on you microphone. It normal for a electret mic element to have a building impedance converter that has around 50 to 100 nv/sqrtHz noise. BJT input opamps such as the AD797...

Maybe the microphone isn't able to drive to ADC to its full range?
Or maybe the ADC input isn't biased halfway its range (3.3V / 2 - 1.65 volt)?
Use the 16 bit ADC bit depth to ensure you dont...

Looks like a cool project, but with only 2 channels ADC, not interesting for me personally.

Then you shouldn’t call it noise.

It is important to keep the impedance to the ADC input as low as possible, so removing that 10k//1n might help. Does it happen when you short the input jack to...

A single coil has about 6nV/sqrtHz noise, a hum bucket about 10nV. That op amp has 18nV noise and that 10k resistor 13nV. And than the ADC... assuming about 10 LSB rms over 20kHz BW and 3.3volt...

For this I have been working on Ethernet. A UDP connection via the Ethernet breakout board.

THD of audio equipment is measured by rejecting the fundamental. That way a scope is fine too.

That would be great.

Somehow I missed this topic, but this looks great!

Are these PCBs for sale, or even the ready made populated PCB. I would like to buy a handful.

High quality audio codecs are benificial for non-music project too! Like ultrasoon, active noise cancelation and hydrophone projects.

This would be great. LabVIEW is a great way to program DAQ programs. It looks a bit like the sound toolbox for teensy. These days there is a free version of LabVIEW availed and I can’t wait to use...

Yeh, thanks for updating this lib��

Very cool��

No. The adc shouldn’t increase current consumption but only draw a few uA.

Any progress on this?

Please let me know if you succeed!

True, better use 3.3V supply to stay save.

Or 6V via 180R to the sensor, to gnd. The ADC connected to the sensor will give readings between 0.3 and 3.0 Volt.

I would asume you would. need a constant current source to feed the sensor. The voltage across the senaor will then be lineairy depended on the sensors resistance.. being 20R to 180R. A constant...

I would model it as a series of impulses, being the explosions in the the cylinders. Then a whole lot of high Q filter to model the transfer function of the cylinder + exhaust. Then increase the...

I see no problem with averaging 4000 samples, allthough 256 should be enough to get the StDev down to 2^-15 FS . I regulairy average traces of 40e3 samples, sampled at 200MHz with a 14bit ADC,...

When I mean 16bit performance, I mean performance equivalent to a typical 16bit ADC IC. Once you get standard deviation of about 2^-15 FullScale, by averaging multiple sample, (e.g. 256 or so) you...

I am sure you can get St.Dev down to 1 with a larger oversampling number, like 128 or so. Then you would have 16bit performace.

Great work, but I am very curious how the ADC performs with a low impedance source, likr 10R or so. A real low noise stable, low impedance source..... cannt you repeat this with a much larger...

Thanks Jnor!

For a measure of DC value, I would definitely choose Median.

You might get a more realistic value by averaging the centre 3, 4, 5, bins or so.

But excluding those single count...

Thanks for sharing, that is good work! And I agree, there isnot enough noise at the ADC input. Too bad there is no 16bit mode.

Do you have a teensy 3.2, 3.6 with which you could repeat this...

A histogram of the raw ADC values, with that 1000uF in place would tell alot about the ADC performance.

You could put large capacitor from ADC input to gnd, e. g. 1000uF. That would provide a low impedance to the ADC input for audio frequencies.

How 'better' exactly?

PS, did you bandwidth limit the adc input?

THx, will look at this!

'To get from 12 bits to 16, I multiply by 16 and add dither.'


Adding noise after an ADC does no good, but increasing noise.

This:

'Median and mode are better measures of central tendency in those cases---although neither increases the resolution of the data. Instead, they act to reduce the noise level in relation to...

Median is a non-linear operation and therefore cannt be used in system-analysis. But it is a excelent method to ignore large sudden signal deviations originating form an intefering process.

So for...

This has nothing to do with teensy. It is very basic signal. processing material. I am not going to do your homework and I am certainly not to put any efforts in teaching you.

Where did you get that from? Not only are you contradicting your self (HF noise is by definition not white). But it is nonsense too.

I do it every day.

you sum all 256 measurement values, and divide by 256.
conviniently, dividing by 256 is the same as bitshifting by 8 which is mucj faster then actual division.

if you average 256 times, you gain 4 bits. 16 bits dynamic range from a 12bit ADC really is no problem at all at low sample rates.

Then it is correlated to the signal. of interest.

inteference will average out, unless it is correlated to the signal. of interest.

You can easely average out a couple of thousand onbaord teensy ADC readings to get the resolution and noise kevel you require.

Following!