<< What is the best method to create a cover song from existing sheet music? In my case I just want to change demo bass track to another bass line from books I purchased OR start with a blank sheet, enter the notes, save it and the replace existing demo bass track. >>

What you're describing is something Band-in-a-Box is optimized to do. It is a particularly good and useful program to learn and become proficient with a musical instrument.

As a company PG Music has prepared a wide variety of song sets performed by some of their professional session musicians that create RealTracks for the company. These songs are grouped by artist and are called Artist Performance Sets. (See screen shots 1 and 2)

As you see in the screen shot text of screenshot 1, these sets use recorded audio and underlying midi for a transcription in notation and tab for the professional players performances that is typically melodies or solos and played over a BIAB SGU song. These are designed and intended as learning tools.

Why this is relevant to your question, is PG Music has provided the tools and features so users can create their own Artist Performance Sets from any performance and they will be the same as the PG Music Artist Performance Sets including notation of the performance.

Users can create their own Artist Performance File as described by PG Music documentation posted in December 2013. (Screen Shot 3)

If there's interest, I can make a second post detailing the tools and steps to create your own custom performance tracks for monolithic instrument performances for melodies and solos performed using bass or guitar solos. Most RealTrack instruments now have Real Charts which is underlying midi that displays accurate notation of the instrument performance and is automatically updated to any changes made to the Chord Sheet such as replacing chords. This allows users to capture great performances from any SGU song and turn it into an Artist Performance Set for practice and learning.

From the BIAB Help File: "Transcribe - This will transcribe the audio as MIDI data and write it into the same track. Note that the audio in the source track should be monophonic (e.g., vocal, saxophone)."

Users with BIAB 2025 have the capability to isolate a bass track from any audio and have it sync with the BIAB program giving users the ability to capture exact performances of their favorite songs and learn the part note for note using the Artist Performance File feature.

Attached Files (Click to download or enlarge) (Only available when you are logged in)
Artist Performance Sets.jpg (153.83 KB, 71 downloads)
Artist Performance set 4 Details.jpg (226.99 KB, 71 downloads)
BIAB's Artist Performance File Feature.jpg (52.58 KB, 70 downloads)
BIAB 2025:RB 2025, Latest builds: Dell Optiplex 7040 Desktop; Windows-10-64 bit, Intel Core i7-6700 3.4GHz CPU and 16 GB Ram Memory.