IIS data conversion problem: 16bit to 24bit

I have a very strange problem today

The request is a 16bit The data is sent to a 24bit Of DAC Play in , As a result, the noise becomes larger ? I don't know why

According to conventional theory ,16bit turn 24bit Just move left 8 Just a little bit

Let's review IIS Drive the logic inside

① Align left :

WCLK For high voltage , It's the left channel , Right channel data at low level

The data starts on the left , low 8 Position as 0

② Right alignment :

WCLK For high voltage , It's the left channel , Right channel data at low level

For example, you collect a negative number 0xc00000, Collected int Type reception may become 0x00c00000, You need to turn it into 0xffc00000

③IIS Pattern

The difference between left and right alignment is WCLK Low power level , It's the left channel , Right channel data at high level , And delay 1 Pulse ( For this standard I2S Format signal, no matter how many bits of valid data , The highest bit of data always appears in WCLK/LRCK change （ That is, the beginning of a frame ） Later 2 individual BCLK/SCLK Pulse place )