Matrix Voice DAC FPGA Code

Hi,

I have a question about the BIT_FRAME_N value in wb_dac.v FPGA code. How does these values are calculated?

/* DAC Sampling Frequency Table
Based in OUT_DATA_FREQ = 4_000_000
FS (KHz) ---- BIT_FRAME_N
8 ---- 975
16 ---- 487
32 ---- 243
44.1 ---- 176
48 ---- 162
88.2 ---- 88
96 ---- 81
*/

Are these values hand tuned for the best quality?
Thanks.