Comparison

S vs Callback Freeverb

Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.

Head to head
About

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.

Highlights
  • 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
Features
Read full description

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.

About

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.

Highlights
  • Classic Freeverb algorithm
  • Schroeder/Moorer reverb topology
  • Comb and allpass filters
  • Mono operation
  • Adds depth and space to audio
  • Smooth, musical reverb tail
Features
Read full description

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

S3 screens
Callback Freeverb4 screens

Verdict

The call

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

CostPrice · In-app purchases · Ads · Monetization

Both are free to download. Neither carries in-app purchases, so what you see is what you pay.

ReceptionRating · Positive reviews · Number of ratings

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.

Scorecard2 real differences · 8 level
S versus Callback Freeverb: the parameters behind the verdict, then further details
ParameterSCallback Freeverb
PriceFreeFree
Rating4.5 (4 ratings)5.0 (1 ratings) — better
Positive reviews0.0% of reviews—
Number of ratings4 — better1
Update frequencyEvery 6 weeks—
AdsNoNo
In-app purchasesNoNo
MonetizationFreeFree
DevicesiPhone, iPadiPhone, iPad
Requires iOS16.0 — better17.0
Further details — not scored
Size17 MB7 MB
Age rating4+4+
DeveloperMathias KirkerødCallback Audio, LLC

Customer experience

S

All ratings4 ratings
Positive75.0%
Neutral25.0%
Negative0.0%
Written reviews1 reviews
Positive0.0%
Neutral100.0%
Negative0.0%

Callback Freeverb

All ratings1 ratings
Positive100.0%
Neutral0.0%
Negative0.0%

In-app purchases

None

S

No in-app purchases

None

Callback Freeverb

No in-app purchases

Questions

Is S free?
S is free to download, with no in-app purchases.
Is Callback Freeverb free?
Callback Freeverb is free to download, with no in-app purchases.
Which has better reviews, S or Callback Freeverb?
Callback Freeverb is rated higher. S averages 4.5 out of 5 from 4 ratings, while Callback Freeverb averages 5.0 from 1 ratings.
Do S or Callback Freeverb have ads?
Neither S nor Callback Freeverb shows ads.

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