Audio Noise on I2S

Using Arduino Audio
1

I'm using a MKRZero to play audio files via I2S using an UDA1334 I2S DAC as an amp.

I've been having a few issues with the quality of the audio playback - initially I was getting stuttering on the playback which I think was caused by a buffer underrun or something. I've solved this by using a different SD card (though I'm still a bit unclear why this worked as the better card is technically the slower one!)

My remaining issue is that when an audio file isn't being played I'm getting a lot of low level white noise on the output. This immediately disappears when a file is played.

I assume it's due to floating levels or something, but I'm not sure how to stop it.

I am using the Arduinosound library and I've noticed it starts by playing a short 'burst' of silence which seems to force the levels low (I assume) and stops the noise.

So I assume I need to decouple something (not sure how to do this) or ground something perhaps? Or is there a simple way to 'hold the output low' to create the silence as per the Audiosound library?

Any suggestions would be gratefully received!

2

Perhaps the library doesn't start driving I2S till first played sample.

Normally the I2S clocks must be driven all the time for a DAC to function properly. If you
stop driving the clocks the DAC will shutdown to standby and the outputs may float - this happens
with phones and mp3 players in my experience.

The output of the UDA1334 is opamp driven, so if those opamps are powered you can't eliminate
the noise - however if they are powered down (no idea, you'd need to experiment), then adding some
extra load to ground on the outputs might help (after the DC-coupling capacitor). Perhaps a few k.

This will reduce the output level somewhat, note.

3

To solve the problem:

Either rewrite the code, so it delivers data continuously

Or add a 1k R from each I2S line to GND. This is a pulldown of the digital signal lines, to keep them from floating when inactive

HTH
Andreas Gaunitz
Electric Gaunitz