Audio broken after changing Audio bitwidth from 16 to 24 in LPCXpresso55S69 EVK.

[delphin]

I have tried to change the Bit width of USB dev_audio_speaker_bm code in SDK version 2.15. I have changed the bitwidth from 16 bit to 24 bit and changed the related macros. But the audio output is not ok, its outputting noises and breaking sounds only. Are there any support document or sites about which changes are required to change the bit width. I have referred application note AN13447.

[Pablo_Ramos]

Hi @delphin,

You can find the code of the Application Note AN13447 in NXP Application Code Hub, you just need to select the device family and search for audio

Link: Application Code Hub (nxp.com)

In there you will find a GitHub link where you can find the code with all the changes that AN13447 mention.

I tested the code, and it works fine, just make sure to delete the file "startup_LPC55S69_cm33_core0.S" that will be added in the startup folder, I don't know why but this file generates some errors in my project.

In order to change how many bits you are using you just need to modify the format of the speaker directly on windows.

This code was made to have 2 modes 16 bits and 32 bits, if you want to use 24 bits you will need to make the pertinent changes in order to do so since there is no other Application Note with that specific requirement.

Also, when I test it with the USB port of my computer, I was only able to use the 16 bits format, I needed to use a USB type C with an adapter in order to be able to use the 32 bits format, this may not be your case but is important make sure that the USBs are not a limitation as it was in my case.

Hope it helps you!

[Jayaprasad_1]

@Pablo_Ramos 

Thanks for pointing to the application note. With the suggested changes I was able to play 32 bit audio, but 24 bit audio is NOT playing continuously through the speaker. The output stream plays through headphone intermittently with breakage.

Could you please check and let me know what additional modifications are required.

The changes I made are

.format = {.sampleRate = kWM8904_SampleRate48kHz, .bitWidth = kWM8904_BitWidth24
audioTxConfig.bitWidth = (uint8_t)kHAL_AudioWordWidth24bits;

#define AUDIO_FORMAT_BITS (24)
#define AUDIO_FORMAT_SIZE (0x03)

And change to USB Audio 1.0 by defining
#define USB_DEVICE_CONFIG_AUDIO_CLASS_2_0 (0U)

[Pablo_Ramos]

Hi @Jayaprasad_1,

In order to narrow down what could be the issue. I recommend you check first on the frame; this means reading with a logic analyzer the encoded audio signal and the I2c signal send to the decoder and do a comparation between the frames of the bitWidth that works and the one that don't.