First, did you read all that thread I linked to, including Brian's concerns about using this method? It could be that using
Zones and
ZoneSwitch would be a better solution for you. There are plenty of examples on the forum for rules to use with ZoneSwitch.
But if you want to use this method...
Configure Auto-Import, either via "Options > Library & Folders > Configure Auto-import" or via the top menu in MC Standard View > Tools > Import > Configure Auto-Import.
Then select the Folder at the top that you have set up for your media files. Let's assume that you have a folder named D:\Music. When you select that folder, and click the Edit button you will see all the parameters for importing media files from that folder. Under "Import these file types" you might only have "Audio" ticked, or possibly "Audio" and "Playlists". You normally don't want to be importing video files found in your Music folder after all.
Below that you have a box titled "Apply these tags (optional)". Click the Add button and you will be able to enter
Expressions to tag files as you wish. Select "Custom", in the drop-down Field list, select "DSP".
You can now enter Fields, Functions, and Variable into the "Value" field to build expressions that control how files are tagged. A very simple expression to set a default value would be;
[DSP]=[Player]
That would select the default Zone of "Player" and its associated DSP settings for all media files imported from that folder.
You might go a bit further and want to use high definition DSP settings for FLAC files, but otherwise use the default Zone, "Player". Try;
ifelse(isequal([File Type], flac), [DSP]=HDPlayer, 1, [DSP]=Player)
Which simply says if the File Type is FLAC, set the Zone to "HDPlayer", otherwise set it to "Player".
A more complex expression might be used to assign different DSP settings to Audio versus Video,
if you were importing both from the same folder. For example;
ifelse(isequal([media type], Audio), [DSP]=HDPlayer, isequal([media type], Video), [DSP]=VPlayer, 1, [DSP]=Player)
Where HDPlayer is an Audio Zone you have set up for playing high definition audio, VPlayer is a Zone you have set up for playing video, and Player is the default Zone in MC, and would be used for any other media types, such as Podcasts. The " 1, [DSP]=Player" is a catch-all if the first two conditions aren't met. I did a couple of simple tests for an audio and a video file, and that expression works.
If you use this method I think you will have to set up a default value for the [DSP] field for all media types, so each Auto-Import folder will need to have a tagging rule added.
Yes, there is a learning curve for using expressions. If you describe exactly what conditions you are using to select a DSP setting, the names of the settings you have created and so forth, someone might help with creating the exact expression or expressions you need.