Static Background Noise (Interference) on the Output Pin When Using RP Pico

[Михаил Шакаев]

Hello everyone! I have encountered significant static background noise on the audio output when using the default output mode (I assume this is MOZZI_OUTPUT_PDM_VIA_SERIAL). I am using a Waveshare RP2040-Plus board, but I have also faced this issue with the original RP Pico. The noise is also present when using the examples, so I think the problem is not in the code.

I tried building a filter as shown in this video, but it did not solve the problem: https://www.youtube.com/watch?v=rwPTpMuvSXg

Solutions I want to try:

1. Using a notch filter
2. Using an external DAC
3. Using the Waveshare pico-audio

I'm writing in the hope that someone has already encountered a similar problem. If you have experience with any of the solutions described above, or if you know another way to solve the problem, or if you simply have comments and suggestions about anything mentioned - please let me know, I would be very grateful.

Thank you all, have a great day!

[tomco...@live.fr]

Hi!

I also encountered great noise levels with the RP2040, at least on the default output mode (which is PWM I think). Especially, there seems to be quite a lot of crossfeed with the ADC (you can hear where you turn a potentiometer).

I think this is due to the fact that the RP2040 is more conceived like a small computer, with not that much focus on analog.

There are a few things you can do though:

 - check this: https://github.com/sensorium/Mozzi/issues/247

 - run from battery usually helps (USB is terribly noisy), or filter heavilly your alimentation

 - using an external DAC (what I am usually doing) is a huge game changer, especially if you are a bit careful on how you provide power to this DAC. This is especially adapted to the RP2040 as it does support I2S natively (and using DMA, hence very little impact on performances).

Hope it helps, do not hesitate to report what you find!

[Михаил Шакаев]

 Hello, thanks for response! 

I just tried the method described in the link, and it made the noise acceptable for testing but still not acceptable for production. Also, I can't avoid using USB because, according to the project concept, USB is used for both powering and charging the built-in battery (the board from Waveshare has a Lithium battery recharge/discharge header, suitable for mobile devices, which allows you to include a battery in the circuit and charge it during use, which I find very cool). I think I should go with the option of using an external DAC. Can you tell me more about this? Which DAC is best to choose as reliable and showing good results with the RP2040 Board?

Additionally, what exactly does "to be a bit careful on how you provide power to this DAC" mean? What measures should I take? Unfortunately, I'm not very strong in electrical engineering, and I may not know some necessary things.

I would appreciate a response, and thanks again for the information provided!

четверг, 20 июня 2024 г. в 13:44:51 UTC+3, tomco...@live.fr:

[Alexander Lee]

Hi, I’ve only tried using the PT8211 DAC with the Pi Pico, but I find the noise and overall sound quality to be even worse than PWM. I don't really know why.

[tomco...@live.fr]

Hi,

Contrary to Alexander I have fairly good results with the PT8211 (do not forget to set the I2S to LSBJ: with Mozzi 2.0: #define MOZZI_I2S_FORMAT MOZZI_I2S_FORMAT_LSBJ). The DAC is not completely monotonic on the LSB but that's a good improvement.

> Additionally, what exactly does "to be a bit careful on how you provide power to this DAC" mean?

That means trying as much as possible to separate digital power line and analog. For most cases, applying the "Application circuit" of the datasheet of the DAC is a very good start. This is true for instance for the PT8211 as it is not regulated: the datasheet is advising for a low-pass filter on the power line and another on the output, that can greatly improve the sound quality (if you have kicad, you can have a look at how I connected it here: https://github.com/tomcombriat/G_TES_touch-synth/tree/main/hardware/v1_1).

More fancy DAC, have also been reported to work fine (the sound quality should be better, but I haven't tested myself): PCM5102 and Max98357A for instance. You can have a look here: https://github.com/sensorium/Mozzi/pull/249

[Михаил Шакаев]

Hello mates!

Alexander, did you try another copies of PT8211 or another copies of rp pico? There is always risk of receiving defective details, may be it was your case?

Tom, thanks for recommendations! Unfortunately, I dont find an opportunity to purchase a PT821, but I easyly can buy PCM5102 and Max98357A, and I think I will try both of it. Thanks!

Have a good day!

воскресенье, 23 июня 2024 г. в 14:03:42 UTC+3, tomco...@live.fr:

[Михаил Шакаев]

Hello friends! I've just got my PCM 5102A module configured according to this description:
https://github.com/dwhinham/mt32-pi/wiki/GY-PCM5102-DAC-module
 

I've tried to run this example: 

https://github.com/sensorium/Mozzi/pull/249/commits/70eb84943b337505aaa9c4fa94b211821cd06e5a

and i'm glad to say that it's work wery well! Tom, thank you for information you provided to me. 

понедельник, 24 июня 2024 г. в 20:49:27 UTC+3, Михаил Шакаев: