There is no such thing as a "project bit depth"
There is a global setting called "Record Bit Depth" in
Preferences > File > Audio Data. "Record Bit Depth" is not stored in the project.
The "Record Bit Depth" may be changed at any time and affects all future audio recordings.
In fact, sample rate is not stored in the project either. Here is how the sample rate and bit depth shown in the Transport Module are determined:
- If there is audio already recorded in the project, the sample rate is set by reading the header of the first audio clip.
- If there are no audio clips in the project, the sample rate is read from "Sample Rate" in Preferences > Audio > Driver Settings.
- The bit depth is always read from "Record Bit Depth" in Preferences > File > Audio Data.
As a rule, "Record Bit Depth" should be set the same as the "Audio Driver Bit Depth" in
Preferences > Audio > Driver Settings. Not sure what the motivation is for "Change Audio Format..." is or why one would change all clips in a project to 16bit.