How to connect external 3.3V I/F I2S signal to nrf5340-audio-dk

[MontBlanc]

Hello,
devzone.nordicsemi.com/.../set-nrf5340-audio-dk-as-i2s-slave-over-external-bus
Based on this post, I changed I2S to SLAVE setting.
The external I2S I/F level is 3.3V.
When OB/EXT is green, it is noisy when I2S of 3.3V I/F is connected to P5, but we have confirmed that the audio signal is sent to the RX side and the sound is heard.

devzone.nordicsemi.com/.../access-to-i2s-interface-on-nrf5340-audio-dk

Based on this post, I tried changing the I2S port.
If OB/EXT lights up orange, does that mean the port has been changed to P10 instead of P5?

But when OB/EXT is orange, there is no sound even if you forcefully connect the 3.3V I/F to P10.

Also, in order to change the 3.3V I/F to 1.8V I/F, I changed the I2S signal level using TI's TXS0108E.
When I connect the nrF5340 to the enabled I2S port (P5 or P10), I checked with an oscilloscope and found that there is quite a lot of noise on the I2S signal.
Since it is a bidirectional buffer, it seems that the noise component is flowing backwards, or the GND level is not stable and crosstalk noise is being buffered.

Is there a way to run nrF5340-audio-DK with 3.3V I/F?
Or is there a good way to make I2S a 1.8V I/F?

[MontBlanc]

Hello,
The latest version when I started working on it was v2.4.2. Since the current latest version is v2.5.0, I will make the same modifications here and try external I2S connection. Please check the modifications to the stereo conversion source code in v2.5.0.

Best Regards.

[Karl Ylvisaker]

Hello again,

Thank you for your patience with this.
Please have a look at this sample based on v2.4.0 as a reference to see the necessary changes to make it a stereo demo.

Best regards,
Karl

[MontBlanc]

Hello, Karl.

Thank you for answering.

Confirmed that the sound is played correctly in external I2S SLAVE mode with v2.4.0,
After that, I implemented all the changes you suggested.

The result is an interrupted mechanical sound that is linked to the played sound.
When there is no sound, there is no sound.
It seems that I2S transmission and reception are not being performed correctly.

If only prj.conf is restored to the original external I2S settings, the audio will be played in monaural with the correct sound.

Therefore, we assume that there is a problem somewhere in the processing branched at HEADSET.
Don't you know what the reason is?

Best Regards.

[Karl Ylvisaker]

Hello,

MontBlanc said:

Thank you for answering.

No problem at all, I am happy to help! :)

MontBlanc said:

Confirmed that the sound is played correctly in external I2S SLAVE mode with v2.4.0,
After that, I implemented all the changes you suggested.

Does this mean that you verified the audio going into the nRF5340 (i.e verified that your external codec provided the correct audio to the nRF), or does it mean that you were able to hear the stereo audio correctly through the LE Audio link when you used the referenced branch as provided, prior to any changes?

MontBlanc said:

The result is an interrupted mechanical sound that is linked to the played sound.

If there are glitches on top of the received audio then there is a chance that something has gone wrong in the handling of the received audio frames.
Could you elaborate further on the question above, so that I better can understand the issue you're seeing?

Best regards,
Karl

[MontBlanc]

Hello,
The environment I tried is as follows.

Environment of external CODEC without using nrf5340
External HOST(I2S SLAVE) - I2S(L/R) - External DAC(I2S MASTER) - L/R ch audio is output from L/R ch

Customized nrf5340 software for external CODEC
External HOST(I2S SLAVE) - I2S(L/R) - nrf5340-audio-dk TX - nrf5340-audio-dk RX(Left) - I2S(Lch) - External DAC(I2S MASTER) - Lch audio is output from Lch
|
- nrf5340-audio-dk RX(Right) - I2S(Rch audio is Lch packet) - External DAC(I2S MASTER) - Rch audio is output from Lch

Environment where I tried to send/receive L/Rch this time
External HOST(I2S SLAVE) - I2S(L/R) - nrf5340-audio-dk TX - nrf5340-audio-dk RX - I2S(L/R ch packet is incorrect) - External DAC(I2S MASTER) - L/R ch audio is output from L/R ch, However, the sound is mechanical

Best Regards.