I noticed the settings regarding Bit Depth in the iMac sound/MIDI unit is set to 24 bit integer for both input and output. Preferred settings in Audacity is 32 bit float for recording.
Should the iMac sound/MIDI settings correspond to Audacity settings 32 bit float or doesn’t it matter?
Audacity works internally with 32-bit float format, and it is best that Audacity is set to use 32-bit float format tracks. It does not matter that the sample format of the capture device does not match, and there aren’t any sound cards that capture as 32-bit.
It is preferable that the sample rate matches. By default this is 44100 Hz in Audacity, which is the rate used for audio CDs.
In the iMac sound/MIDI unit it is possible to set the format to 32-bit floating. It is possible to set 8, 16, 32, 44,1, 48, 88,2, and 96 kHz each with 16, 20, 24 and 32-bit format but maybe the sound card don’t capture higher than 24-bit format. anyhow the sample rate is matching!