S vs Callback Freeverb
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
S
This app is a polyphonic synthesizer that works with specific hardware. It offers a variety of sound engines, filters, and effects for creating unique audio textures. Advanced modulation options and a flexible routing system allow for deep sound design.
- Dual engine slots per voice
- Multiple sound flavors (analog, wavetable, FM, speech)
- Classic and Modern filter modes
- Advanced FX rack
- Two free-routing LFOs
- Unified mod matrix
- Standalone, AU, and AUv3 formats
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s-2 is a polyphonic synthesizer designed to work with the Roland AIRA Compact S-1. ENGINE Each voice runs two parallel engine slots that mix together. Pick a sound flavor per slot, including: • Classic analog — saw, square, sub, noise, pulse-width • Wavetable • FM • Speech • Chord • Plucked string FILTER AND FX Classic mode runs a vintage-style ladder filter into a simple Delay → Chorus → Reverb chain. Modern mode swaps in a multi-mode SVF (LP / BP / HP) followed by a 3-slot Advanced FX rack with Bitcrusher, Drive, Flanger, Phaser, Auto-Filter, Tape Delay, Plate Reverb and Chorus. MODULATION Two free-routing LFOs (sine / triangle / saw / square / random / noise, with optional clock-sync), a dedicated filter envelope with two destination slots, and a unified mod matrix dialog that visualizes every routing in one place. Click any knob in Learn mode to assign — no digging through menus. FORMATS • Standalone for iOS • Audio Unit (AU) for Logic Pro and other AU hosts • AUv3 plugin for iPad / iPhone in AUM, GarageBand, Cubasis and more - s-2 is an independent third-party application. It is not affiliated with, sponsored by, or endorsed by Roland Corporation. "Roland", "AIRA", "AIRA Compact", and "S-1" are trademarks of Roland Corporation, used here only to describe MIDI compatibility between this app and that hardware.
Callback Freeverb
This app offers a classic algorithmic reverb effect based on the Freeverb algorithm. It adds depth, space, and atmosphere to audio sources, creating lush, spacious ambience. Designed for mono use, it provides a smooth, musical reverb tail suitable for vocals and synthesizers.
- Classic Freeverb algorithm
- Schroeder/Moorer reverb topology
- Comb and allpass filters
- Mono operation
- Adds depth and space to audio
- Smooth, musical reverb tail
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A classic algorithmic reverb effect based on the Freeverb algorithm by Jezar at Dreampoint. A Freeverb-style Schroeder/Moorer reverb based on the classic 8-comb + 4-allpass topology, with simplified controls and no stereo spread. This reverb creates lush, spacious ambience through a network of comb and allpass filters. Freeverb is widely used in electronic music production, ambient music, and sound design to add depth, space, and atmosphere to audio sources. The algorithm provides a smooth, musical reverb tail that works well on everything from vocals to synthesizers. This reverb only functions in mono and provides no stereo imaging, and the user can expect the same behavior as a classic Freeverb implementation otherwise.
Screenshots
Verdict
The clearest difference is rating: Callback Freeverb at 5.0 against S's 4.5. S's advantage is ratings volume (4 vs 1). On price, 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
Both are free to download. Neither carries in-app purchases, so what you see is what you pay.
Callback Freeverb holds the better App Store score, 5.0 against 4.5. Both are backed by a comparable volume of ratings — 4 and 1 respectively.
| Parameter | S | Callback Freeverb |
|---|---|---|
| Price | Free | Free |
| Rating | 4.5 (4 ratings) | 5.0 (1 ratings) — better |
| Positive reviews | 0.0% of reviews | — |
| Number of ratings | 4 — better | 1 |
| Update frequency | Every 6 weeks | — |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Free | Free |
| Devices | iPhone, iPad | iPhone, iPad |
| Requires iOS | 16.0 — better | 17.0 |
| Further details — not scored | ||
| Size | 17 MB | 7 MB |
| Age rating | 4+ | 4+ |
| Developer | Mathias Kirkerød | Callback Audio, LLC |
Customer experience
S
Callback Freeverb
In-app purchases
S
No in-app purchases
Callback Freeverb
No in-app purchases





