Neo-trellis sound hissing

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luckenbach
 
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Neo-trellis sound hissing

Post by luckenbach »

While playing audio back from the NeoTrellis I get an odd 'hissing' sound along with whatever is being played. The welcome wav along with all the drums and any other wav i add to the board for that matter get this "effect" applied to them. Anything I should be looking for specifically to address this?

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adafruit_support_mike
 
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Re: Neo-trellis sound hissing

Post by adafruit_support_mike »

That sounds like low-level random noise.

Do you hear the same hiss when the output should be silent, or only when one of the sounds is playing?

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luckenbach
 
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Re: Neo-trellis sound hissing

Post by luckenbach »

If the audio subsystem is "engaged" it will make noise. If I take control over the board with the REPL and make it not run code.py the output is silent. I can record a video of it on the demo code tonight. Watching others videos they def behave differently audio wise compared to mine.

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luckenbach
 
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Re: Neo-trellis sound hissing

Post by luckenbach »

Fair warning the noise is rather heinous

https://drive.google.com/file/d/1vGpZ21 ... sp=sharing

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adafruit_support_mike
 
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Re: Neo-trellis sound hissing

Post by adafruit_support_mike »

That's definitely wrong. The noise sounds like high-speed data though, so there's a faint chance that it could be a software issue.

Let me check with the folks who wrote the firmware for the NeoTrellis and see if they have any guesses.

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luckenbach
 
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Re: Neo-trellis sound hissing

Post by luckenbach »

In efforts to address this I did flash the latest firmware. No difference.

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johnpark
 
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Re: Neo-trellis sound hissing

Post by johnpark »

That's not something I've heard before -- could you try headphones instead of powered speakers, as well as a USB phone charger battery to power the Trellis M4? Just to decouple things a bit.

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luckenbach
 
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Re: Neo-trellis sound hissing

Post by luckenbach »

so moving to a wall-wart plug has made the level the hissing radically lower; with my IEMs on its still pretty noticeable, I have to turn up my powered speakers a bit to hear it but it is very metronomic with some occasional dubstep thrown in.

https://drive.google.com/file/d/1xZbvPK ... sp=sharing

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adafruit2
 
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Re: Neo-trellis sound hissing

Post by adafruit2 »

yep thats serial data being transfered probably, the USB port is noisy. this is the trade off of going with plain DAC output as opposed to I2S. its' meant to be a simple audio playback toy, not audiophile quality :)

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luckenbach
 
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Re: Neo-trellis sound hissing

Post by luckenbach »

So the noise in the initial video is "expected"?

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theshaggyfreak
 
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Re: Neo-trellis sound hissing

Post by theshaggyfreak »

Yep. I believe this is the USB data that we're hearing. I have the same problem as well but it disappears when I run it from a battery.

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adafruit_support_mike
 
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Re: Neo-trellis sound hissing

Post by adafruit_support_mike »

The source of the issue will be a ground loop through the power supplies.

Ideally, the only connection between an audio source and the power amplifier is a two-line 'balanced' audio signal. The amp's input can measure the voltage between the signals without needing any other information. In most cases the input signals also pass through series capacitors so no DC current can flow through the input wires.

If the audio source and amplifier share any other DC connection, like to a common power source, you get new paths for signals to travel. If there's noise on the shared power lines, some of that noise will also travel through the audio signal lines.

There's no way to build an audio signal loop that's immune to ground-loop noise. If the noise is present, the rest is basic physics.

There are only two ways to deal with ground-loop noise: avoid having a ground loop altogether, or make sure any shared ground loop you have remains quiet.

Moving your powered speakers to a different power supply, and possibly a different wall outlet, will help reduce the noise that can pass through the ground loop. Running one leg of the power through an inductor with strong high-frequency attenuation can also help.

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