For the AD1939 CODEC, data sheet specifies sample rates of 128/176.4/192 kHz if you set control register to '10'. We did that and are at 192 kHz. How do we get 128 kHz instead ? That's the ADC/DAC sample rate we really want. Thanks.
Notice that for each setting there are three sample rates shown.
Note that this register setting only adjusts a divider to divide the master clock.
So here is the list again but with the divider added that divides down from the master clock.
32/44.1/48kHz, MCLK divided by 256
64/88.2/96kHz, MCLK divided by 128
128/176.4/192kHz, MCLK divided by 64
So which of the three sampling rates you get depends on the master clock rate.
If you use a 12.288MHz master clock then the three register settings will give you 48, 96, or 192kHz fs.
So you will need to change the master clock to be 128 x 64 = 8.192MHz.
This is still within the range of the PLL so all you need to do is change the crystal to an 8.192MHz crystal ( or change the master clock source ) and you will be running at 32, 64 or 128kHz sampling rates.