7.10.13. STRUDEL-13 — SF2 SoundFont Playback

Sample banks are great for drums but painful for pitched instruments — a single kick sample works fine at any note, but a piano needs dozens of samples across the keyboard. The General MIDI SoundFont format (.sf2) packs a whole orchestra of multi-sampled instruments into one file, with a standard preset numbering that makes playback portable.

daStrudel loads GM SoundFonts directly and dispatches notes to SF2 presets through the usual pattern chain.

7.10.13.1. Part A: Loading a SoundFont

strudel_load_sf2 reads a .sf2 file and activates it for the next patterns. It returns true on success:

require strudel/strudel_player

if (!strudel_load_sf2("FluidR3_GM.sf2")) {
    print("failed to load SoundFont\n")
}

One SoundFont is active at a time; reloading replaces the previous one. Any General MIDI SoundFont works — FluidR3_GM, GeneralUser GS, Musyng Kite, Stolen Soundfont. Larger fonts have more samples and sound better.

7.10.13.2. Part B: Instruments by Name or Number

Two ways to pick an instrument:

// By GM program name — looked up in the SoundFont's preset table
let piano <- note("c3 d3 e3 f3 g3 a3 b3 c4") |> sf2("piano") |> gain(0.6)

// By program number (0..127) — the raw GM program code
let flute <- note("c4 e4 g4") |> sf2(73) |> gain(0.5)

Common GM program numbers:

Program	Instrument
0	acoustic grand piano
24	nylon guitar
40	violin
56	trumpet
73	flute
81	lead square

Use the program number when the name lookup does not match the preset names in your SoundFont, or when you want a specific patch.

7.10.13.3. Part C: GM Drums on Bank 128

The GM percussion kit lives on bank 128 — every MIDI note number is a different drum. Switch to it with sf2(0) |> sf2_bank(128) and play the drum map directly:

let drums <- note("c2 ~ d2 ~, [fs2 fs2] [fs2 fs2] [fs2 fs2] [fs2 fs2]") |> sf2(0) |> sf2_bank(128) |> gain(0.7)

Key drum mappings (octave 2):

Note	Drum
c2 (36)	bass drum
d2 (38)	snare
eb2 (39)	hand clap
cs2 (37)	side stick
fs2 (42)	closed hi-hat
as2 (46)	open hi-hat

7.10.13.4. Part D: Expression and Velocity

Pitched SF2 presets respond to two kinds of per-note dynamics:

velocity(v) — attack intensity (0..1) — changes timbre as well as level
sf2_expression(e) — continuous volume (0..1) — pure level control

Together they drive realistic phrasing. This example stacks two string layers at different expression levels to thicken the pad:

let pat <- stack([
    note("<[c3,e3,g3] [f3,a3,c4]>") |> sf2("string_ensemble") |> sf2_expression(0.3) |> gain(0.5),
    note("<[g3,b3,d4] [a3,c4,e4]>") |> sf2("string_ensemble") |> sf2_expression(1.0) |> gain(0.5)
])

SF2 playback in daStrudel is a daslang-only extension — there is no equivalent in strudel.cc. See daslang strudel vs strudel.cc — Feature Comparison for the full list of daslang-only features.