PCM2903C: 1kHz Noise during recording

Michael Liesenberg85

Mastermind 7560 points

Part Number: PCM2903C

Hi,

i am using the PCM2903C to record audio data and i am playing it back in a different soundcard connected to PC.

I notice that i have a 1kHz noise in the signal. Is there a way to reduce it?

This thread didnt helped me

since i have a good GND connection with a 6 layer PCB.

Any idea?

Maybe i have to play the recorded sound back to PCM2903C and on the same time to the other sound card to the computer and mabe this noise will go away.

The Line Out from PCM2903C are not connected to anything, i use only to record sound.

over 7 years ago

0 Diego Melendez over 7 years ago

TI__Guru 57800 points

Hi, Michael,

This issue was actually fixed on the B and C versions of the codec, so you should not be seeing the noise. Have you verified the same behavior on the EVM?. Can you see the tone even if the input is disconnected?

Regards,

-Diego Meléndez López
Audio Applications Engineer

0 Michael Liesenberg85 over 7 years ago in reply to Diego Melendez

Mastermind 7560 points

Hi Diego,

the 1kHz goes away if i leave the input pins open.

Maybe a need a better supply power?

0 Michael Liesenberg85 over 7 years ago in reply to Michael Liesenberg85

Mastermind 7560 points

Hi Diego,
so i added a Low ESR 330uF Elec Capacitor directly to 5V and the 1kHz noise was quieter.
I added one more in parallel and the 1kHz noise got even more quieter but still on the background.

The Elec Capacitor will take too much space, is there a better solution?

0 Michael Liesenberg85 over 7 years ago in reply to Michael Liesenberg85

Mastermind 7560 points

So here is my schematic, maybe it can be improved.

Soundcard:

USB Type C Input Connector:

Voltage Regulator:

0 Michael Liesenberg85 over 7 years ago in reply to Michael Liesenberg85

Mastermind 7560 points

The 1kHz noise has gone now. What i did was to connect all VCC together and take 5V from an other source and include an extra LDO for 5V to 3V3.
There is a backgroud noise still but below 200Hz i think.

So using a different 5V Source from the audio signal with its own 3V3 LDO makes the 1Khz USB noise goes away.

0 Diego Melendez over 7 years ago in reply to Michael Liesenberg85

TI__Guru 57800 points

Hi, Michael,

Thanks for sharing the details of your solution. The problem seem related to the power supply used, so using a specific supply for the PCM device is a good idea. I noticed in your schematic that SEL0 is tied to GND, however, it should be tied to logic high level (VDD).

Best Regards,

-Diego Meléndez López
Audio Applications Engineer

0 Michael Liesenberg85 over 7 years ago in reply to Diego Melendez

Mastermind 7560 points

Hi Diego,
SEL0 is tied to 3V3

Audio

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PCM2903C: 1kHz Noise during recording