Instruments (also known as MIDI program changes) are represented as in the MIDI specification using integers from 0 to 127. That’s a total of 128 timbre settings. The music library defines the following instrument constants for convenience:

ACOUSTIC_GRAND, PIANO = 0
BRIGHT_ACOUSTIC = 1
ELECTRIC_GRAND = 2
HONKYTONK_PIANO, HONKYTONK = 3
EPIANO1, RHODES_PIANO, RHODES = 4
EPIANO2, DX_PIANO, DX = 5
HARPSICHORD = 6
CLAVINET = 7
CELESTA = 8
GLOCKENSPIEL = 9
MUSIC_BOX = 10
VIBRAPHONE, VIBES = 11
MARIMBA = 12
XYLOPHONE = 13
TUBULAR_BELLS = 14
DULCIMER = 15
DRAWBAR_ORGAN, ORGAN = 16
PERCUSSIVE_ORGAN, JAZZ_ORGAN = 17
ROCK_ORGAN = 18
CHURCH_ORGAN = 19
REED_ORGAN = 20
ACCORDION = 21
HARMONICA = 22
TANGO_ACCORDION, BANDONEON = 23
NYLON_GUITAR, GUITAR = 24
STEEL_GUITAR = 25
JAZZ_GUITAR = 26
CLEAN_GUITAR, ELECTRIC_GUITAR = 27
MUTED_GUITAR = 28
OVERDRIVEN_GUITAR = 29
DISTORTION_GUITAR = 30
GUITAR_HARMONICS = 31
ACOUSTIC_BASS = 32
BASS, ELECTRIC_BASS, FINGERED_BASS = 33
PICKED_BASS = 34
FRETLESS_BASS = 35
SLAP_BASS1 = 36
SLAP_BASS2 = 37
SYNTH_BASS1 = 38
SYNTH_BASS2 = 39
VIOLIN = 40
VIOLA = 41
CELLO = 42
CONTRABASS = 43
TREMOLO_STRINGS = 44
PIZZICATO_STRINGS = 45
ORCHESTRAL_HARP, HARP = 46
TIMPANI = 47
STRING_ENSEMBLE1, STRINGS = 48
STRING_ENSEMBLE2 = 49
SYNTH_STRINGS1, SYNTH = 50
SYNTH_STRINGS2 = 51
CHOIR_AHHS, CHOIR = 52
VOICE_OOHS, VOICE = 53
SYNTH_VOICE, VOX = 54
ORCHESTRA_HIT = 55
TRUMPET = 56
TROMBONE = 57
TUBA = 58
MUTED_TRUMPET = 59
FRENCH_HORN, HORN = 60
BRASS_SECTION, BRASS = 61
SYNTH_BRASS1 = 62
SYNTH_BRASS2 = 63
SOPRANO_SAX, SOPRANO_SAXOPHONE = 64
ALTO_SAX, ALTO_SAXOPHONE = 65
TENOR_SAX, TENOR_SAXOPHONE, SAX, SAXOPHONE = 66
BARITONE_SAX, BARITONE_SAXOPHONE = 67
OBOE = 68
ENGLISH_HORN = 69
BASSOON = 70
CLARINET = 71
PICCOLO = 72
FLUTE = 73
RECORDER = 74
PAN_FLUTE = 75
BLOWN_BOTTLE, BOTTLE = 76
SHAKUHACHI = 77
WHISTLE = 78
OCARINA = 79
LEAD_1_SQUARE, SQUARE = 80
LEAD_2_SAWTOOTH, SAWTOOTH = 81
LEAD_3_CALLIOPE, CALLIOPE = 82
LEAD_4_CHIFF, CHIFF = 83
LEAD_5_CHARANG, CHARANG = 84
LEAD_6_VOICE, SOLO_VOX = 85
LEAD_7_FIFTHS, FIFTHS = 86
LEAD_8_BASS_LEAD, BASS_LEAD = 87
PAD_1_NEW_AGE, NEW_AGE = 88
PAD_2_WARM, WARM_PAD = 89
PAD_3_POLYSYNTH, POLYSYNTH = 90
PAD_4_CHOIR, SPACE_VOICE = 91
PAD_5_GLASS, BOWED_GLASS = 92
PAD_6_METTALIC, METALLIC = 93
PAD_7_HALO, HALO = 94
PAD_8_SWEEP, SWEEP = 95
FX_1_RAIN, ICE_RAIN = 96
FX_2_SOUNDTRACK, SOUNDTRACK = 97
FX_3_CRYSTAL, CRYSTAL = 98
FX_4_ATMOSPHERE, ATMOSPHERE = 99
FX_5_BRIGHTNESS, BRIGHTNESS = 100
FX_6_GOBLINS, GOBLINS = 101
FX_7_ECHOES, ECHO_DROPS = 102
FX_8_SCI_FI, SCI_FI = 103
SITAR = 104
BANJO = 105
SHAMISEN = 106
KOTO = 107
KALIMBA = 108
BAGPIPE = 109
FIDDLE = 110
SHANNAI = 111
TINKLE_BELL, BELL = 112
AGOGO = 113
STEEL_DRUMS = 114
WOODBLOCK = 115
TAIKO_DRUM, TAIKO = 116
MELODIC_TOM, TOM_TOM = 117
SYNTH_DRUM = 118
REVERSE_CYMBAL = 119
GUITAR_FRET_NOISE, FRET_NOISE = 120
BREATH_NOISE, BREATH = 121
SEASHORE, SEA = 122
BIRD_TWEET, BIRD = 123
TELEPHONE_RING, TELEPHONE = 124
HELICOPTER = 125
APPLAUSE = 126
GUNSHOT = 127