Digital noise from line output of Teensy Audio Shield

A

aarontroughton

New member
Hello everyone,

I have uploaded a recording of the line output of the teensy audio shield playing wav audio from the SD card on the Teensy 4.0 board:

Teensy Audio Example (Google Drive)

You can hear it right at the start of a track and throughout playback. Comes through as a distorted high pitched pulsing tone which I'm assuming is crosstalk from the card reader?

Does anyone know why I'm getting digital read noise spilling into the audio output? I have tried all kinds of noise cancellation stages, nothing seems to get rid of it. Im curious why its there in the first place as I don't get this on the 3.5mm headphone output...

Any insight would be great, please let me know whether you need any further info on the circuit.

Many thanks
 
The headphone output has its own separate ground, whereas the line-out shares ground with the micro SD card, so the large current spikes taken by the SD card on writing/erasing inject noise direct to this ground.
 
Please understand several different problems can have similar effect, so diagnosing this sort of noise involves guesswork.

A very common problem in called "ground loop". This can happen in the circuitry of Teensy and the audio shield and other nearby parts. But the very common (and usually much worse sounding) ground loop problem happens over a physically much larger scale, where the loop is formed by the USB cable, your computer's connection to the AC mains ground, and up the power cable to the audio system and through the line-level audio cable ground. Again, please know this is some guessing on my part, but I'd suggest focusing first on the huge ground loop through all your gear.

You have a 3 possible ways to deal with the large ground loop.
Audio problems from large ground loops are such a common problem that many of these isolator products are made.

You might also be experiencing a smaller, more localized ground loop. They do happen, and sometimes the effect is also pretty bad, but usually localize ground loops have relatively small effects that are difficult to hear. That's why I'd suggest focusing on the giant loop through the USB cable, audio line-level cable, and whatever power cords your computer and audio system use.
 
You must log in or register to reply here.
Back
Top