Audio codec noise

Audio codec noise

by Loïc Ted Ferrot -
Number of replies: 1


 In our mini project we would like to implement a DSP, meaning audio in - processing - audio out. However we are struggling against a strong audio noise when using the WM8731 audio codec from the DE1 board, something between a loud "crackling" and a white noise.

It seems a bit magical to us, since the noise seems to have different characteristics (and sometimes even disappear) from one quartus build to another, even though the eventual changes are not linked to the audio part, or if the exact same design is compiled again. In our design the avalon streaming sources are directly connected to the avalon streaming sinks from the same Altera audio module, i.e. no processing.

We also know that the DAC is working fine thanks to Alexandre Chau and his mini project from last year that we could run without noise.

One suspect is the ADC of the module, not involved in Alexandre's design. Even when configuring the codec with only the microphone as input, and with the microphone muted in the codec configuration (and/or physically disconnected), the noise could be heard.

The configuration itself of the codec through I2C seems to work fine, using the logic analyzer the signals transmitted correspond to what is expected and the correct behavior can be observed.

Has anyone experienced the same problem? Is it possible that there is some kind of "stochasticity" in the quartus build? Worst case we can just build the same design until we get a noise free version, but it seems like dark magic, and I would be glad to understand what is happening...

In reply to Loïc Ted Ferrot

Re: Audio codec noise

by René Beuchat -


The noise could come from different sources:

  1. the microphone
  2. the connector
  3. the ADC
  4. the ADC reading
  5. in the FPGA if the algorithms are not correct
How do you detect your noise?

Depending on the compilation of quartus means that you have noise induces by the power supply, I think. 

Do you catch the data from the ADC synchronously without latches? Verify if your compilation warning specify some latches somewhere in your design.

Good luck.