@hiroshiy, I've played around with this quite a while this morning. Here's what I found:
- Just for clarity, let's first remember, Tesla's MP doesn't use ALBUMARTIST as it should. It uses ARTIST instead. So, it's "my" dBpoweramp conversion settings that are really copying your source ALBUMARTIST tag data into ARTIST for use with MP.
- NOTE: While my settings strip out any tags that MP does not currently use (to perhaps save memory or just a bit of CID processing time), I do purposely leave ALBUMARTIST in the converted tracks on the hope that one day Tesla will fix their design flaw, and anyone that has used "my" conversion settings will have a USB device with tracks that will work properly on the first day that new firmware becomes available.
- I made a number of test VBS tracks with "Unknown" in varying combinations as ARTIST, ALBUMARTIST, TITLE, and ALBUM. I tried both the original hand-tagged test files, as well as ran them through "my" dBpoweramp conversion process. My MS (2018.6.1) accepted and played them all without any problem, duplication or unexpected breaking-up of albums.
- Looking back at my dBpoweramp DSP settings logic, I have always had it place the word "Unknown" into the converted version of either ARTIST or ALBUMARTIST if the tag is non-existent or blank in the source track. I revalidated this morning (dBpoweramp for Mac V16.2) that if that change is made by my processing logic, physical file naming will also show "Unknown" as it should.
- I did find a couple obscure scenarios where my conversion logic could fail and end-up producing a bad physical filename or where ALBUMARTIST or ARTIST get out-of-sync with one another -- which could cause album splitting or other anomalies as you found. I won't bore you with detail, but non-existent tags or blanks in the source ALBUM, TITLE, TRACK (number), ALBUMARTIST, or ARTIST could be the culprit.
So, I can't explain why your MS isn't liking "Unknown" in the ARTIST tag, as mine seems to be OK with it. Regardless, I'm providing an updated "1a" version of my dBpoweramp settings that will hopefully resolve this for you in the future, and I've hopefully made the conversion logic more robust for everyone if critical tag data is missing in the source track. How to use the attached settings file is the same as I described upthread last November.
V1A CHANGE LOG:
- CHANGE: If ARTIST or ALBUMARTIST is non-existent or blank in the source version of any track, "Various Artists" (in lieu of "Unknown") is now inserted in the converted track tag and used for any file naming purposes.
- ADDED: If ALBUM or TITLE is non-existent or blank in the source version of any track, "Not Specified" will be inserted in the converted track tag and used for any file naming purposes.
- ADDED: If TRACK (number) is non-existent or blank in the source version of any track, "1" will be inserted in the converted track tag and used for any file naming purposes.
- CHANGE: I restructured some of the DSP processing logic to ensure ALBUMARTIST & ARTIST are kept in-sync even better than before when exceptions are encountered in the source library
- NOTE: Coding remains in place to handle if DISC (number) is non-existent or blank in the source version of any track, where a "1" is inserted in the converted track tag and used for any file naming purposes.
I know you've manually made changes to fix the problem you had, but hopefully this updated set of dBpoweramp DSP settings are a little more robust to fend-off future issues for us all. Let me know if you have problems with this new update. I've done testing with a few dozen test tracks that include a lot of exceptions, but not my full 7K set of tracks I run with in my MS, as that takes nearly 3 days on my quad core 4gHz iMac to complete, and I'm confident I have clean data in all the critical tags of my source library.
My best.