Crystal Synth XT vs GSDSP Quantum Filter
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
Crystal Synth XT
Create lush, evolving soundscapes with a powerful semi-modular synthesizer for mobile devices. Explore subtractive and FM synthesis, extensive modulation, and built-in effects. Share sounds with the desktop version and connect MIDI keyboards for a full hardware synth experience.
- Semi-modular synthesis engine
- Subtractive and FM synthesis
- Extensive modulation control (>90 parameters)
- Multi-stage envelopes with graphical editors
- Tempo-synced envelopes, LFOs, and delays
- Built-in effects (chorus, flanger, echo)
- MIDI keyboard input and virtual MIDI support
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Crystal Synth XT is a full featured semi-modular synthesizer, ideally suited to creating lush evolving soundscapes. Crystal VST has long been a popular synthesizer on the desktop. Crystal Synth XT brings that same powerful synthesis engine to the iPad and iPhone. Crystal Synth XT features MIDI keyboard input via Apple's camera adapter and sharing of sounds with the desktop version of Crystal. == Features == Browse through the included sounds and use the 2 octave keypad or keyboard to trigger notes to produce evolving, rhythmic, or melodic sounds. Create your own sounds with a single button press using the breed feature. When using an iPad, you can delve into a tweaker's dream by using the extensive editing features to sculpt sounds to your heart's content (editing features are only available when used on an iPad). Crystal features both subtractive synthesis and frequency modulation (FM) synthesis. It offers abundant modulation control with over 90 parameters which may be modulated, multi-stage envelopes with graphical editors, extensive tempo sync of envelopes/lfo rates/delay times, built-in effects for chorus/flanging/comb filtering/echoes, and a band splitter for effects processing by frequency band. Not only that, Crystal has wave sequencing and granular synthesis. The musical applications for Crystal are literally boundless. == MIDI == With MIDI keyboard input, you can connect a MIDI keyboard to your iPad or iPhone and play Crystal Synth XT like a hardware synth. == Virtual MIDI == Use virtual midi to play Crystal Synth XT from a midi controller app. Use the Settings app to turn on the Background Audio mode to enable Crystal to play audio when in the background. You can then play Crystal from a midi controller app which supports virtual midi. == Sharing == With patch sharing you can create sounds on your iPad or iPhone while away from the studio, then transfer them to the desktop Crystal when you get back to the studio to use in recording projects. Or, create banks of sounds on the desktop Crystal, then transfer them to the iPad/iPhone Crystal to use in a live performance for a truly portable rig. Use Audio copy/paste to record your performance on Crystal and transfer that performance to another app. Or copy your recorded performance to your computer. == Inter App Audio and Audiobus == To use IAA or Audiobus to record into other apps, turn on Background Audio for Crystal Synth XT in the Settings app. See demonstration videos on the greenoak.com website. == Different Versions == If you don't need all the features of Crystal Synth XT, try the basic version of Crystal, also available in the app store from Green Oak Software. With the basic version you can browse sounds, play notes, and create new sounds, taking advantage of its powerful semimodular synthesis engine. The XT version adds features like MIDI keyboard input via the iPad's camera adapter, IAA/Audiobus, and patch sharing with the desktop version. Choose the app that is best for you! == Notes == Important note for iPhone users: Crystal Synth XT runs on both the iPad and the iPhone. Because of the limited screen space on the iPhone however, the editing pages, which contain the edit controls, are not available when running on that device. However, on the iPhone you can still browse sounds, play notes from the keypad, create new sounds with the Breed feature, modify patches with the Design feature, and share sounds with desktop Crystal VST. For videos and information about Crystal Synth XT, visit: http://www.greenoak.com
GSDSP Quantum Filter
This audio effect plugin offers analog-modeled filters with flexible routing and dynamic modulation for creative sound design. It provides extensive control over tone shaping and complex filtering with various filter types and configurations.
- Analog-modelled filters
- 11 filter modes
- Series and parallel routing
- Dynamic modulation support
- Stereo and dual mono modes
- MIDI control integration
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Analog warmth meets flexible routing and dynamic modulation in a filter workstation built for creative sound design. Analog-Modelled Filters Quantum Filter uses resonant, analog-modelled filter designs that behave smoothly and musically across the entire spectrum. With no cramping, stepping, or digital artefacts, the filters remain stable even under rapid modulation. At high resonance settings they can reach self-oscillation, similar to classic hardware circuits. Filter Types & Routing Choose from 11 filter modes, including Lowpass, Highpass, Bandpass, Notch, Shelving options, Bell, and Ladder Lowpass in 1–4 pole configurations. Combine filters in series (up to three stages) or parallel (up to two), resulting in over 2,000 possible routing combinations for detailed tone shaping and complex layered filtering. Built for Modulation Designed to handle fast, artefact-free modulation, Quantum Filter responds cleanly even under rapid parameter changes. Its stability makes it suitable for dynamic environments, rhythmic modulation, or complex movement across multiple filter stages. Stereo and Dual Mono Switch between stereo and dual mono modes to shape the stereo image. In dual mono mode, left and right channels can move independently, enabling asymmetric movement, wider imaging, or separate modulation paths for each side. MIDI Control Quantum Filter integrates ADSR & AR modulators that respond directly to MIDI, allowing envelope-driven filter motion that behaves like a synthesizer’s filter section. This integration adds expressive control for rhythmic gating, animated sweeps, and dynamic shaping based on your playing or sequencing. Quantum Filter is an AUv3 audio effect plugin compatible with Logic Pro, AUM, Cubasis, GarageBand and many more. A Desktop version is also available for Windows and macOS (VST3 / AU / AAX). More information here: https://gs-dsp.com/products
Screenshots
Verdict
The clearest difference is price: Crystal Synth XT at $4.99 against GSDSP Quantum Filter's $14.99. Crystal Synth XT also leads on ratings volume (20 vs 3). GSDSP Quantum Filter's advantage is review sentiment (100% vs 78%) and update cadence (every 5 weeks vs every 4 months). On rating, ads, in-app purchases and monetization model there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Crystal Synth XT costs $4.99 and GSDSP Quantum Filter $14.99 up front. Neither carries in-app purchases, so what you see is what you pay.
On the App Store both sit at effectively the same score — 4.9 for Crystal Synth XT against 5.0 for GSDSP Quantum Filter. That said, the two scores are not equally well evidenced: Crystal Synth XT has 20 ratings behind it against 3, so its average is the more settled of the two. Written reviews are what separate them: 78% of Crystal Synth XT's written reviews are positive against 100% of GSDSP Quantum Filter's.
Crystal Synth XT ships an update every 4 months, GSDSP Quantum Filter every 5 weeks. The most recent releases landed on September 21, 2026 and September 22, 2026 respectively.
| Parameter | Crystal Synth XT | GSDSP Quantum Filter |
|---|---|---|
| Price | $4.99 — better | $14.99 |
| Rating | 4.9 (20 ratings) | 5.0 (3 ratings) — better |
| Positive reviews | 78.4% of reviews | 100.0% of reviews — better |
| Number of ratings | 20 — better | 3 |
| Update frequency | Every 4 months | Every 5 weeks — better |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Paid | Paid |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Requires iOS | 11.0 — better | 12.0 |
| Further details — not scored | ||
| Size | 36 MB | 77 MB |
| Age rating | 4+ | 4+ |
| Developer | Green Oak Software | Gustav Scholda |
Customer experience
Crystal Synth XT
GSDSP Quantum Filter
Bugs and requests
Crystal Synth XT
Reported bugs
15 issues- App not working, splash screen disappears
- Screen in background
- Envelope points not moving
- Breed fan not working properly
- Crashing on launch
Show 10 moreShow fewer
- Clicks and crashes when adjusting parameters
- Sounds distorted and buggy
- Won't play any sounds
- Crashes when hitting record
- Play surface stopped responding
- Crash when trying record function
- Crackles and pops in sound engine
- Audiobus fails, breaks up when switching apps
- Preset name editing gone after iOS 7 update
- Splash screen appears for a second, then disappears
Requested features
22 requests- AUv3 support
- Update to an AU3 standard
- Newer interface
- Fix breed fan access to all presets
- Fix preset system variations between devices
Show 17 moreShow fewer
- AUv3 implementation
- Update the envelope points
- AUv3 standard transformation
- Multiple instances in DAWs
- Dark mode option
- Advanced analytics dashboard
- Fix preset name editing
- In-app purchase for a second instance
- Load/Save banks
- Metronome or timer capability
- Newer app icon
- Redesign for Retina Display
- Polyphony on iOS version
- Recording facility
- Keyboard option
- Virtual MIDI support
- Advanced patch editing on iPod version
GSDSP Quantum Filter
Not enough reviews yet to summarise bugs or requests.
In-app purchases
Crystal Synth XT
No in-app purchases
GSDSP Quantum Filter
No in-app purchases
Questions
Is Crystal Synth XT free?
Is GSDSP Quantum Filter free?
Which has better reviews, Crystal Synth XT or GSDSP Quantum Filter?
Do Crystal Synth XT or GSDSP Quantum Filter have ads?
Which is updated more often, Crystal Synth XT or GSDSP Quantum Filter?
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