Flex Music LabsLearn
GuitarFlex vs Spitfire Audio guitars
Spitfire Audio's Soft Nylon Guitar and Soft Acoustic Guitar are sampled acoustic guitars for Kontakt Player, on Windows and Mac, at $99 and $149. GuitarFlex is modeled, not sampled: presets for steel-string and nylon-string acoustic and electric clean, crunch and heavy guitars, a download of 18.2 MB, and $79.
What they have in common
- Windows 10, with guitars you play from MIDI.
- Nylon-string and steel-string acoustics. Spitfire has one library for each, and GuitarFlex has presets for both.
- Slides, hammer-ons and pull-offs. Spitfire's libraries play them. GuitarFlex plays them too, when ComposerFlex's parts ask for them.
Where Spitfire's guitars stand out
- Mac as well as Windows, with macOS 11 to 26.
- A chord and strum engine. Soft Acoustic Guitar has one, with a 4-bank, 32-step sequencer and MIDI drag and drop, so held chords become a part. GuitarFlex has no strum patterns of its own.
- Patterns. Soft Nylon Guitar comes with a MIDI pack of 163 patterns.
- A range of articulations, including mutes, harmonics, trills, bends and body hits, with up to 5 round robins and 4 velocity layers in Soft Nylon Guitar.
- Capo placement, and custom tunings in Soft Acoustic Guitar.
- Recorded guitars, where GuitarFlex plays no recordings.
Where GuitarFlex stands out
- Electric guitars too. Presets for clean, crunch and heavy electrics, with an amp, a cabinet, reverb and an eight-band EQ.
- No other program. Spitfire's guitars need Kontakt Player and the Spitfire Audio App. GuitarFlex runs on its own, as a standalone program and a VST3 plugin.
- A stated size. GuitarFlex is an 18.2 MB download that installs at 43.9 MB. Soft Nylon Guitar is 776.6 MB, and Soft Acoustic Guitar is a 2.1 GB download.
- No account and no online activation. A license key and your email address, entered once for each Windows user on each computer, and one license for one person, to use on all of their own computers. It never connects to the internet. Spitfire states that its installation needs the internet.
- $79, against $99 and $149.
- Your own settings. Over 70 sliders and four slots (A to D) to switch between sounds or layer them, with Compare, Vary and Randomize.
- Your song to a file. It renders a MIDI file to FLAC, or to WAV with the included command-line renderer.
- Built to play ComposerFlex's band, our songwriting program, on the same PC with no setup. With ComposerFlex it plays down and up strums, with Strum spread and Strum fall.
Which to pick
- On a Mac: Spitfire.
- For a strum engine and sequencer that turn held chords into a part: Spitfire's Soft Acoustic Guitar.
- For electric and acoustic guitars in one small program, at $79: GuitarFlex.
- If you'd rather have no second program, no account and no online activation: GuitarFlex.
Owning both
Spitfire's libraries are recordings and GuitarFlex is a model, so they can share one PC: Spitfire for its recorded acoustics, GuitarFlex for electrics and for parts from ComposerFlex. GuitarFlex's demo is here; for Spitfire, go by its own pages. This page doesn't compare how they sound. That's for your ears.
The facts side by side
Every fact about Spitfire Audio guitars is from Spitfire Audio's own pages, checked on 7 November 2026. Prices are list prices in US dollars; sales come and go.
| GuitarFlex | Spitfire Audio guitars | |
|---|---|---|
| How it makes its sound | Modeled. It computes every note as you play, from the physics of plucked strings: the acoustic presets sound through the guitar's body, and the electric presets through a pickup, an amp and a cabinet. It plays no recordings. | Sampled: a small-bodied nylon-string guitar and a steel-string acoustic guitar (the maker's words). |
| Price | $79, one-time | Soft Nylon Guitar $99; Soft Acoustic Guitar $149; no sale shown |
| Download and disk space | 18.2 MB download, 43.9 MB installed | Soft Nylon Guitar 776.6 MB; Soft Acoustic Guitar 2.1 GB download |
| Memory the maker asks for | 4 GB, with 4 cores or more and 100 MB of disk (the minimum we state for every Flex program) | Not stated on the maker's pages |
| Runs on | Windows 10 and 11, 64-bit | Windows 10; macOS 11 to 26 (Kontakt 8.8 needs macOS 14); an internet connection is needed during installation |
| Forms | Standalone and VST3 | Through Kontakt Player (the formats are not stated on the product pages) |
| Needs another program | Nothing else | The free Kontakt Player (5.8 or later for the nylon guitar, 6.7.1 or later for the steel-string) and the Spitfire Audio App |
| Copy protection | A license key and your email address, entered once for each Windows user on each computer. No account and no online activation. | Not stated on the maker's pages |
| Computers per license | One license for one person, to use on all of their own computers | Not stated on the maker's pages |
| Demo | A demo to download and try before you buy | Not published |
| Guitars included | Presets in groups: steel-string and nylon-string acoustic, electric clean, crunch and heavy, and a two-guitar band preset; four slots to layer sounds | Soft Nylon Guitar: slurs (hammer-ons and pull-offs), trills and slides, up to 5 round robins and 4 velocity layers, 7 tunings, capo placement, and a free MIDI pack of 163 patterns. Soft Acoustic Guitar: a chord and strum engine, a 4-bank 32-step sequencer, MIDI drag and drop; mutes, harmonics, slides, slurs, vibrato, bends and body hits; standard and custom tunings; 5 effects |
More: virtual guitars compared: modeled and sampled, a table of 25 products, and all about GuitarFlex.
If something here is out of date, write to [email protected] and we'll correct it.