Samples in the SAMPLE engine's built-in sets. All CC0 1.0 (public domain).

PIANO  VCSL (Versilian Community Sample Library), Grand Piano (Steinway B), sustain, close mics
       (until 2.1 the piano was VCSL's Upright Piano (Knight), DUSTY; it is no longer in the tree)
VIBES  VCSL, Vibraphone (hard mallets)                    https://github.com/sgossner/VCSL
BASS   VSCO-2 Community Edition, Solo Contrabass pizzicato
HORNS  VSCO-2 Community Edition, Trumpet + Tenor Trombone staccato
STRGS  VSCO-2 Community Edition, Violin + Viola sections spiccato
FLUTE  VSCO-2 Community Edition, Flute (susvib)           https://github.com/sgossner/VSCO-2-CE
SCRCH  Sonic Pi sample set (freesound.org CC0 recordings): vinyl_scratch (hello_flowers),
       vinyl_backspin (il112), vinyl_rewind (TasmanianPower)
       https://github.com/sonic-pi-net/sonic-pi/tree/main/etc/samples
KIT    VCSL: the acoustic drum kit of the GM map (bass drum, snare, side stick, claps, hi-hat, toms,
       suspended cymbal, cowbell) and hand percussion (tambourine, shaker, conga, claves, woodblock)

Thanks to Versilian Studios / Sam Gossner and to the Sonic Pi project.
Retuned, cut and coloured by tools/gen_builtin_hiphop.py (gen_hiphop_pack.py's chain).