PCM1808: High output noise level

Khoi Le

Part Number: PCM1808

Tool/software:

Hi team,

On behalf of my customer, I would like to post a question to seek your guidance:

The wav file is captured using tinycap (bitrate 16, sample rate 48khz), as you can see in the screenshot between 5.0 and 6.0 sec in the white marked area, the white noise is high and permanent.

Our clock configuration:

- use in slave mode

- SCKI: 12.288Mhz

- LRCK: 48 kz

- BCK: 3.072 Mhz

Please let me know if you need any additional information. Thank you.

11 months ago

0 Daveon Douglas 11 months ago

TI__Mastermind 27510 points

Hi Khoi,

From a hardware perspective the customer can try to implement a RC filter at the input stage or a bandpass filter that is targeted to customer input signal.

On the ASI clocks, you can try to reduce BCLK to (2ch * 16bit * 48khz) = 1.536MHz

I would also check schematic for proper decoupling of the power supply as this can be a common source for noise and transients in the system.

0 Khoi Le 11 months ago in reply to Daveon Douglas

TI__Intellectual 1196 points

Hi Daveon,

Thanks for the recommendation. I have sent the schematic via email to you.

0 Daveon Douglas 11 months ago in reply to Khoi Le

TI__Mastermind 27510 points

Hi Khoie,

Thanks for sharing offline. There are no concerns that I see.

Can you share an oscilloscope view of your ASI clocks?

0 Tuan Lam 11 months ago

Prodigy 40 points

Hi Daveon Douglas

Thanks for the analysis, here is the screenshots of clock LRCK and SCKI as requested:

SCKI clock LRCK clock

Thank you

0 Jeff McPherson 11 months ago in reply to Tuan Lam

TI__Mastermind 47195 points

Hi Tuan,

Daveon is out of office and will return to answer your question on Monday. Please wait for a response for him.

Thank you,
Jeff McPherson

0 Tuan Lam 10 months ago in reply to Jeff McPherson

Prodigy 40 points

Dear Jeff and Daveon

Any update on this issue? Can you explain the root cause of the white noise as I described?

Thanks

Tuan

0 Tuan Lam 10 months ago in reply to Tuan Lam

Prodigy 40 points

Dear Daveon

According to your recommendation, BCK can be changed to 1.536MHz, how to change LRCK and SCKI accordingly?

Thanks

Tuan

0 Daveon Douglas 10 months ago in reply to Tuan Lam

TI__Mastermind 27510 points

Hi Tuan,

Since the device is in i2s mode the BCLK should be greater than or equal to 2 Ch * 16bit word length * 48kHz FS = 1.536MHz.

Fsync should remain 48kHz. SCKI can remain 256*Fs at 12.228MHz. In the oscilloscope view you want to check that the clocks are the correct frequencies and synchronized so that audio is processed clear without any distortion.

It is important that these are synchronized in this device due to its fade-in architecture. Otherwise, you will see distortion, this is explained in section 7.3.3 of the d/s.

Try recording a 1kHz sine wave and note the response for a better analyzation of the issue.

0 Daveon Douglas 10 months ago in reply to Tuan Lam

TI__Mastermind 27510 points

[deleted]

0 Tuan Lam 10 months ago in reply to Daveon Douglas

Prodigy 40 points

Hi Daveon

Thanks for advise, we will try to change the clock and hope it will help

Tuan

Audio

Audio forum

PCM1808: High output noise level