Sound Quality Issues on the LPC4357

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by dennislumiad on Tue Jun 09 11:38:39 MST 2015
Hi all,

I am facing problems while using the I2S peripheral of the NXP LPC4357. I am using the CMSIS lib and in principle everything works fine for a 44,1KHz mono wav file with a 16 bit word width. However, when I switch to an 8KHz mono wav file with a 16 bit word width, problems are showing up.

In the specs I found that a 16KHz signal is the lowest the I2S peripheral can go. Therefore, I configured it with a 16KHz config and send every sample of my wav file twice to the output buffer.
My question concerns the sound quality. When I am playing the mentioned 8Khz wav file on a 16KHz I2S configuration, the produced sound has a whistle in itself and is more or less deformed. Has anyone face this problem before? Or does anyone understand where this comes from?

For the 44,1KHz wav file a 12MHz clock is fed to the I2S peripheral.
For the 8KHz wav file a 240KHz clock is fed to the I2S peripheral.

Many thanks in advance for your time and consideration!