Go to the auto generated code for SAI configuration, search the line I mentioned in my post, change it. If you want to know how it's calculated, study the example of NUCLEO-WB55RG, @Federica Bossi Hope the ST firmware team can fix this.    

This is a bug of CubeMx code generation, I figured it out from the example Federica Bossi provided. The value generated below can't be used. hsai_BlockA1.Init.AudioFrequency= SAI_AUDIO_FREQUENCY_8K;Use the equation in NUCLEO-WB55RG example to change ...