It uses your existing samples (RealTracks Holds) that you paid PG music for so I can't really upload them to give away for free.
If you just put the free sfz's from Band-in-a-Box-Sounds.bank-RealBass-2.zip in the Hold folders it will work as long as you have the uncompressed wav in there.
Just drag
Acoustic String Bass (33) Hold 73.sfz,
Finger Electric Bass (34) Hold 125.sfz
or Finger Electric Bass (34) Hold 125 (Direct Input).sfz
from their folder straight into Sforzando, you can also make an alias for them on your desktop.
The other bit is if you want to add them to the PG Sforzand Library for quick access.
It does work really well and is well worth trying for adding custom bass riffs to a RealTrack Bass or for a whole midi track. You can easily create a break in the RealBass for a bass solo simply using F5 to mute the RealBass playing and bring in the midi track playing Acoustic String Bass (33) Hold 73.sfz then F5 back to normal and allow the RealBass to come back in.
PG could include these quite easily for users and maybe get around to sampling the non bass instruments to sfz giving uses a lot more control.

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Holds_73.png (14.48 KB, 170 downloads)