Optical SPDIF Rx Recording has "Alias" frequency of "Fs/2-f"

[James Chan]

Hi,

My HW use XU216, I'd like to enable Optical SPDIF input and output. My software is based on "sw_usb_audio-[sw]_6.15.2" reference code.

The SPDIF Tx works well, I can record stream by another sound card.

But when I try to record Optical SPDIF Rx to a wave file, it seems there is always a "Alias" frequency of Fs/2-f.
For example, if the Optical SPDIF signal sent from another sound card is 8kHz, sampling rate is 48kHz, then the recorded wave has two frequency: 8kHz and 16kHz (=48kHz/2-8kHz).
I tested same issue in both 44.1kHz and 48kHz sampling rate.




Did anyone met this issue before? Any suggestion what is the potential issue?

Thanks
James

[James Chan]

According to spectrum, it looking like every other sample was set to 0. but can't figure out where did it happened?

zero_samples.png

The recorded wave form shows every other samples are zeros:

Recorded_Waveform.png

Hi,

My HW use XU216, I'd like to enable Optical SPDIF input and output. My software is based on "sw_usb_audio-[sw]_6.15.2" reference code.

The SPDIF Tx works well, I can record stream by another sound card.

But when I try to record Optical SPDIF Rx to a wave file, it seems there is always a "Alias" frequency of Fs/2-f.
For example, if the Optical SPDIF signal sent from another sound card is 8kHz, sampling rate is 48kHz, then the recorded wave has two frequency: 8kHz and 16kHz (=48kHz/2-8kHz).
I tested same issue in both 44.1kHz and 48kHz sampling rate.




Did anyone met this issue before? Any suggestion what is the potential issue?

Thanks
James

[James Chan]

Issue solved. The SPDIF Rx channel overlapped with ADC channel.