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TOPIC: ADC Noise Software Solution.

ADC NOISE SOFTWARE SOLUTION! 2 years 11 months ago #657

  • BowDown
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The noise consists of high frequencies?
Do we know exactly the frequencies we need to cut off?
I think about designing a hardware filter prior to the output jack
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ADC NOISE SOFTWARE SOLUTION! 2 years 11 months ago #658

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There are at least 2 sources of noise:
- The power supply: The pedalsHIELD board has a nice power supply but the Arduino board could introduce noise. Changing the power supply makes a big difference so maybe looking into the Arduino board itself could help.
- High freq noise, maybe a better reconstruction filter after the dac may help. You can start filtering freqs over 5KHz, it is a reasonable cut off freq for a digital guitar pedal.
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ADC NOISE SOFTWARE SOLUTION! 2 years 9 months ago #684

  • AndrewHPavei
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Hi Ray, i guess that isnt a good idea cut all frequencies over 5khz, Most musical instruments produces high frequencies. the reasonable idea is cut over 20-22Khz due our ear limitation.
(Ofcourse , depends on the limitation of the amplificator or record sound system, most of than records in 44.1 hz)
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ADC NOISE SOFTWARE SOLUTION! 2 years 9 months ago #685

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It would be ideal to cut over 20KHz and keep all freqs below, but using the Arduino hardware and ADCs/DACs you need to find a balance point.
If you filter at 20KHz instead of 5KHz you will end up with a lot of aliasing noise because the ADCs/DACs cannot sample fast enough. Anyway if you want to give a try is quite simple just replace the 270pF caps for something between 68 and 82pF but I do remember using a bigger audio band during the pedalSHIELD due development and getting too much noise.

In a nutshell the cut frequency of the filters is a balance between noise and wider audio frequencies.
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ADC NOISE SOFTWARE SOLUTION! 2 years 9 months ago #689

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Hello. I want to experiment with placing a filter before the output. Since my board is already soldered, i was considering soldering some pins or piece of metal to the GROUND and SIGNAL pins of the output jack of my board.. Then i would have my filter and then another output jack on a breadboard for experimentation. The thing is... I don't know what the pins of the output jack do...

I checked the datasheet of the output jack but i found no luck in it. Then i checked the schematic of the pedalshield... This shows that the output jack has two pins connected to ground and one which is the signal... Then what the other three pins do?

I guess finding the signal pin is easy, just use the sinewave generator effect and plug some multimeter until you find the pin that actually has a voltage.

But do i have to ground these other two specific pins? Which pins do i need to ground? Can you help my identify which pin is which?

Thanks a lot!
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ADC NOISE SOFTWARE SOLUTION! 2 years 9 months ago #692

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Hi,
The tip of the jacks are signal and the two other pins (ring and sleeve) are ground.
So looking at the jacks (input or output) the most inner pin is signal and the two others in the middle and outer are ground.
r321_9_image_jack-2.png


You have to take care also because when you insert a jack only on row of the pins are connected to the jack itself. Inserting a guitar jack you can see how the pins are separated on the top of the connector.

22.png


You just need to connect any of the 2 gnd pins.
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ADC NOISE SOFTWARE SOLUTION! 2 years 9 months ago #693

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Thanks a lot!

Then i guess the other 3 pins from below, are just symmetrical to the 3 pins on the top... They are the same pins, in other words..
1. Do i have to ground both of the ground pins? The ground should be the same that the pedalshield board has, right?
2. Can i use smd components for my filter? Actually can you use smd components at all when dealing with audio electronics? Pedalshield, as well as all the pedals you have analyzed on the electrosmash website, have through hole components. Why is that? Can you use smd components instead?

Thanks!
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ADC NOISE SOFTWARE SOLUTION! 2 years 9 months ago #694

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Then i guess the other 3 pins from below, are just symmetrical to the 3 pins on the top... They are the same pins, in other words..
Nope, If you have a close look, when you introduce the jack the other 3 pins are separated, and with a multimeter you can see that they are floating, so they are not connected to anything when the jack is in. Do not use them.
1. Do i have to ground both of the ground pins? The ground should be the same that the pedalshield board has, right?
One is enough but if you want to ground both there is no harm. The ground of the pins and the ground of pedalshield is the same.
2. Can i use smd components for my filter? Actually can you use smd components at all when dealing with audio electronics? Pedalshield, as well as all the pedals you have analyzed on the electrosmash website, have through hole components. Why is that? Can you use smd components instead?
If you have easy access to smd components you can use them, pedalshield is designed with through hole because from the hobbyist point of view they are easier to work with.
There is another debate about smd VS through hole for sound quality, but that is another story, for this particular circuit you wont find any sound differences.
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ADC NOISE SOFTWARE SOLUTION! 2 years 9 months ago #702

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Thanks a lot!
As a question that arose from what you said...

There are two capacitor categories in the pedalshield. Ceramic and electrolytic.
What are the differences between them? Can you swap from one to another?
And how does that translate to the smd world... As far as i know there is only one smd capacitor category.. there are all the same

Thanks!
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ADC NOISE SOFTWARE SOLUTION! 2 years 9 months ago #704

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There is a fantastic article about capacitors for guitar pedals effects by Dano from BeavisAudio.
Unfortunately his website is not longer available but I have a PDF backup of his work:

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File Name: beavis-audio-research-capacitors-article.pdf
File Size: 1,182 KB


Have a look at it, I am sure it would help you, it is a piece of art.
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