Comparison

Callback Freeverb vs K.O. II

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

Head to head
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.

About

K.O. II

Features
Read full description

K.O. II is a compact native beat-making instrument for iPhone and iPad. Tap responsive pads, switch between drum, percussion, bass, and key banks, build 16-step patterns, and explore 38 included demo grooves. Designed as a focused standalone music surface, K.O. II gives you a hardware-inspired workflow for quick ideas, rhythm practice, and portable sound experiments.

Screenshots

Callback Freeverb4 screens
K.O. II1 screens

Verdict

The call

Callback Freeverb and K.O. II are too close to call on the numbers: across 5 compared parameters — price, ads, in-app purchases and device support among them — neither pulls far enough ahead to decide it. What separates them is feature set and interface, not measurable difference.

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.

ScorecardNo meaningful differences
Callback Freeverb versus K.O. II: the parameters behind the verdict, then further details
ParameterCallback FreeverbK.O. II
PriceFreeFree
Rating5.0 (1 ratings) — better—
Number of ratings1 — better—
AdsNoNo
In-app purchasesNoNo
MonetizationFree—
DevicesiPhone, iPadiPhone, iPad
Requires iOS17.016.0 — better
Further details — not scored
Size7 MB1 MB
Age rating4+4+
DeveloperCallback Audio, LLC海洋 符

In-app purchases

None

Callback Freeverb

No in-app purchases

None

K.O. II

No in-app purchases

Questions

Is Callback Freeverb free?
Callback Freeverb is free to download, with no in-app purchases.
Is K.O. II free?
K.O. II is free to download, with no in-app purchases.
Do Callback Freeverb or K.O. II have ads?
Neither Callback Freeverb nor K.O. II shows ads.

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