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?

[Karl Ylvisaker]

Hello,

Thank you for your extreme patience with this, and for the clarifications.

MontBlanc said:

nrf5340-audio-dk RX(Right) - I2S(Rch audio is Lch packet) - External DAC(I2S MASTER) - Rch audio is output from Lch

Is the only issue here that the R channel audio is output from the L channel? Is the audio quality as expected, and equal to the audio output on the nRF5340-audio-dk RX(left) that is acting as the I2S master?

MontBlanc said:

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

Are you here configuring the headset device to be an I2S slave to the External DAC as the I2S master? In this case, I would assume that the output could be distorted since the nRF5340 is not in control of the I2S interface, and so it can not adjust the frequency of the MCLK to compensate for the drift in the reception timestamp.
Could you share some of your implementation here, so that I can take a look at how you are handling the packet reception and output?

Best regards,
Karl

[MontBlanc]

I made the changes below.

main.c
#include <hal/nrf_gpio.h>

and added
nrf_gpio_cfg_output(21);
nrf_gpio_pin_set(21);
inside
int main(void){}

audio_system.c
"ret = hw_codec_init();"
delete

hw_codec.c
Change all "return ret" in to "retuern 0"

Are there any other changes?

audio_i2s.c

.mode = NRF_I2S_MODE_SLAVE, // MODIFIED
.format = NRF_I2S_FORMAT_ALIGNED, // MODIFIED
.alignment = NRF_I2S_ALIGN_LEFT,
.ratio = NRF_I2S_RATIO_256X, // MODIFIED
.mck_setup = NRF_I2S_MCK_DISABLED, //0x66666000, MODIFIED

[MontBlanc]

Hello,

CONFIG_TRANSPORT_BIS=y was set extra.
When this setting was removed, L/R monaural transmission was possible.
The results are below.

.format = NRF_I2S_FORMAT_I2S
.alignment = NRF_I2S_ALIGN_LEFT

.sample_wodth = NRF_I2S_SWIDTH_16BIT
Lch Silent, Rch OK, No noise

.sample_wodth = NRF_I2S_SWIDTH_16BIT_IN32BIT
Lch Silent, Rch OK, No noise

.sample_wodth = NRF_I2S_SWIDTH_24BIT
Lch OK, Rch Silent, small noise mixed

.sample_wodth = NRF_I2S_SWIDTH_24BIT_IN32BIT
Lch OK, Rch Silent, small noise mixed

.sample_wodth = NRF_I2S_SWIDTH_32BIT
Lch OK, Rch Silent, No noise

I'd like to send and receive in stereo, but it's not working.
What should I fix?

Best Regards.

[MontBlanc]

In addition, the specifications of I2S are
LRCK=48kHz
BCLK=64Fs
16bit I2S (Left alignment)
is input to nrf5340 on the sending side.

[MontBlanc]

Hello,

After reviewing the source code again and rewriting it, the sound now plays correctly.
Referring to the post below, is the bitrate of LC3 default to 96kbps?

devzone.nordicsemi.com/.../range-of-config_lc3_bitrate

I'm making the same changes, but the build doesn't work.
I would like to check the trade-off between delay and sound quality, but what should I do if I want to change the bitrate after changing to external I2S?