Noise Floor in Digital Domain Spectrum During Sine Wave Playback on ADSP-21568
Dear Team,
We tried to verify the example code located at
C:\Analog Devices\EV-2156x_EZ-KIT-Rel3.0.0\EV-2156x_EZ-KIT\Examples\drivers\adc\ADAU1372_Talkthrough\EV-SOMCRR-EZLITE\21568\ADAU1372_Talkthrough_21568.
During testing, we checked the analog recording we observed that the sine wave noise floor levels were higher than expected.
However, when using ADAU1466 SigmaDSP boards for recording the sine tone, the noise floor was not observed.
Also please find details of our setup and error snapshot attached.
Regards,
Sundaram
Thread Notes
Sundaram37 - Moved from CrossCore Embedded Studio and Add-ins to SigmaDSP Processors & SigmaStudio Dev. Tool. Post date updated from Thursday, November 6, 2025 6:53 AM UTC to Monday, February 2, 2026 6:51 AM UTC to reflect the move.
Sundaram37 - Moved from CrossCore Embedded Studio and Add-ins to SigmaDSP Processors & SigmaStudio Dev. Tool. Post date updated from Monday, February 2, 2026 6:51 AM UTC to Monday, February 2, 2026 6:51 AM UTC to reflect the move.
Audio Signal Processors
software
SigmaDSP Audio Processors
CCES 3.0.3
adsp-21568
Hi Sundaram,
Apologies for the delay in response.
We tested the BSP example using 1kHz sine wave input and measured the DAC output in Tektronix mixed signal scope. The noise floor appears around ~60 dBm which is consistent with the scope's own internal noise level. So we are expecting the actual noise will be much lower than the one observed via scope. The ADAU1372 codec itself has an SNR of around 90 dB. Please also verify the signal at your input side and ensure that the source is clean.
Please refer the probe image here.
Best Regards,
Santhakumari.V
Hi Santhakumari,
We checked the input source file, and it is clean.
We have attached the input streams for your reference.
Play this audio clip
We have interfaced the ADAU1466 board for digital recording(Spdif), but the output is still disturbance. Please share your feedback.
Regards,
Sundaram
Hi Sundaram,
Apologies for the delay in response.
We are unable to open the attached audio clip on our end. Could you please zip the file and share it again?
We also have a few questions to better understand the setup:
1. Which tool are you using to record the output audio?
2. On the SigmaDSP board, are you using the internal oscillator block as the sine tone input, or providing an external analog input?
3. Could you please explain the complete recording setup and the tools used?
This information will help us debug the issue further.
Looking forward to your response.
Best Regards
Santhakumari.V
Hi Santhakumari,
Sorry for the inconvenience
I have attached my input source as a ZIP file.
3060.input_source.zip
1)Which tool are you using to record the output audio?
>> Spectra lab tool is used to record the audio output.
2.On the SigmaDSP board, are you using the internal oscillator block as the sine tone input, or providing an external analog input?
>> Yes, the internal oscillator is used as the sine tone input.
3.Could you please explain the complete recording setup and the tools used?
>>We are using an ADAU1466 board, configured through SigmaStudio v4.5, to provide SPDIF input to the ADSP-21568 board. The ADSP-21568, programmed using CCES 3.0.3, receives this input, processes the data, and then transmits it back to the ADAU1466 board through the recording SPDIF output.
Regards,
Sundaram
Hi Sundaram,
Apologies for the delayed response.
I tested multiple setups on my side and observed the following behavior :
When using the internal oscillator at 0 dB as input → ADSP-21568 → ADAU1372, some harmonics were observed at the output.
When using the internal oscillator at –10 dB as input → ADSP-21568 → ADAU1372, no harmonics were observed.
Could you please try this setup on your side and let me know your observations?
Best Regards,
Santhakumari.V
Please log in to reply.