How to generate UBM file?

Hi,
Thank for your project.
In the example, the UBM file **("../ubm/ubm")** is needed and you created by yourself.
```go
vprEngine, err := NewEngine(16000, 50, "../ubm/ubm", "model/test.dat")
```
Can you please tell me how to generate the UBM file by myself?
Thank you