Noisy DAC output! Help?

dac output noise level

I tried to build my own audio codec using couple of ADC and DACs manufactured by Crystal.
For this purpose I choose ACD CS5341 and the DAC CS4341. I developed prothotype PCB compliance all described Crystal recomendations.
After my first tests, I am very confused form the results. The noise of the DAC output is very high even it is assigned in RESET mode /state/
I just can not believe that the 'noisy' result on the output is normal.
Maybe I am doing something wrong, or maybe I am missing something....

I will be glad if anybody can help me.

Regards,
stroma

dac output noise

How strong is the noise compared to full-scale?
What type of noise is it? Broadband hissing, whistles, buzzing, ...?
Maybe an FFT would reveal some clues.

noisy dac

Hi echo47
The noise sounds like white noise. You can see attached picture taken from my scope /sorry about bad quality/. Noise level is about 40-50 mV p-p. The FFT of the noise looks like repeated peaks with period of about 800 kHz between them. Sampling frequency is 15.625 kHz and design is 5V powered. I thing I have PCB layout/decoupling problem. Could you have a look on my design /2 pdf attached in my first post/ and make some suggestions about PCB design.
Thank in advance.
stroma

Your scope snapshot (and probably your FFT) shows only ultrasonic switching noise. It's way too high frequency to be audible. Maybe it's just a false signal picked up by an oscilloscope probe and ground clip. Have you eliminated that possibility?

How are you monitoring the audio output quality? If you are feeding it into an amplifier, maybe it's the noisy device. Or maybe the amplifier is reacting badly to the ultrasonic switching noise.

Try to find some way to measure the amplitude and hopefully spectrum of only the audio noise below 20 kHz. Also try to determine if the noise is coming from the ADC section or the DAC section.

I'm not familiar with those codec chips, however PCB layout problems usually don't cause white noise.