Noise in headphone output

aditya · ‎2017-09-14

Posted on September 14, 2017 at 13:50

I'm using STM32f4-Discovery board for an audio application.

I'm using the onboard codec CS43L22, in analog passthrough mode. But I'm getting high frequency noise on the output over headphones.

Can anyone tell what could be the possible reason for this noise and what might be the solution?

#cs43l22 #audio-codec #stm32f4 #stm32f4discovery-audio-codec #discovery #adc-noise

Vangelis Fortounas · ‎2017-09-15

Posted on September 15, 2017 at 11:06

Hi.

You mean you have noise without some input signal ?

Is the correct AnalogIN input selected?

If for example you have selected the input from PDM_OUT, you hear the digital ''noise'' of microphone.

If you have selected the input from DAC_OUT...Make a test , configure the DAC_OUT PA4 as GPIO PP output in low state. Observe for noise. If noise exists the CS43L22 is not correctly intialized or has some HW malfunction.

aditya · ‎2017-09-15

Posted on September 15, 2017 at 11:25

Hi Vangelis,

Thank you for your reply.

I'm taking input from an external analog mic. The flow is Mic -> ADC -> DAC -> Codec

You mean you have noise without some input signal ?

-In the above flow, even if I don't give any input to ADC, there is some noise. (Some frequency components-4kHz, 4.5kHz, 16kHz).

Is the correct AnalogIN input selected?

-Yes. I'm using AIN1A, AIN1B.

Selected input is DAC_OUT.

If noise exists the CS43L22 is not correctly initialized

- Can you help with initialization?

Thank You

Vangelis Fortounas · ‎2017-09-15

Posted on September 15, 2017 at 12:36

Hello again.

I can't help you by giving you the correct sequence of register values must put in CS43L22( i don't have time to study the registers)

But in general (with some study also)

Initialize I2C port to communicate with cs43l22 (PB9, PB6)

initialize PD4 pin as reset pin to cs43l22 (GPIO PP output)

Apply the reset sequence (by the datasheet) after power on.

and ... begin to send via I2C, the commands to initialize the cs43l22.

aditya · ‎2017-09-19

Posted on September 19, 2017 at 13:11

I configured the codec as per the instructions stated in the datasheet.

Still the noise persists. Without any input to the ADC, there is noise.

Also without any input to the ADC, while debugging...DR shows some values like 40, 80, 7E etc.