Comparison

Theremin I/O vs Theremin Synth

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

Head to head
About

Theremin I/O

Transform your iPhone into a touchless musical instrument using your camera and flash. Control sound generation by hand proximity, with options for scales, sound presets, and effects. An in-app purchase enables MIDI controller functionality.

Highlights
  • Touchless instrument control via camera
  • Adjustable scales and harmony quantization
  • Multiple sound presets with effects
  • MIDI controller functionality (in-app purchase)
  • Interactive tutorial overlay
Features
Read full description

Play with light – Theremin I/O turns your iPhone into a touchless music instrument. It uses your camera and flash to measure the distance to your hand, this signal is then processed by a synthesizer to generate a tone. Features: • Old-school synthesizer • Constrain input to scales (harmony quantization) • 8 sound presets with effect controls • 50+ scale presets • Use as a MIDI controller (requires in-app purchase) • Learn fast with the tutorial overlay For more information visit http://theremin.io

About

Theremin Synth

Create unique soundscapes with this multitouch synthesizer. Record, loop, and overdub your creations, then export them as WAV files to share. Experiment with various waveforms and effects for endless sonic possibilities.

Highlights
  • Multitouch synthesis
  • Record, loop, and overdub
  • Adjustable delay, feedback, and scuzz effects
  • Four waveform options
  • Export recordings as WAV files
  • Offline functionality
Features
Read full description

This is a multitouch synth instrument. Play it by touching and swiping the screen, changing the waveforms and sliding the effects to create anything from traditional sci-fi theremin sounds to deep scuzzy soundscapes. Use the looper controls to record, loop and overdub layers. Then if you wish to save or share your recording, hit the download button to send your wav file to other compatible apps like Messages, Email, Dropbox etc. The original Theremin went live in 2014 on the web at femurdesign.com/theremin. Over a million hits later and hundreds of requests for a record button, I have redesigned it. Now the Theremin is ready for you to experiment with. Happy playing! -- SPECIFICATIONS -- • Record, loop and overdub options. • Multitouch allows up to 8 tones to be played simultaneously with your fingers • 3 sliders: delay, feedback and scuzz • 4 waveforms: sine, square, triangle and saw • No internet needed, works both online and offline • Download the loop as a .wav file • Loops can be shared with other apps like Mail, Message and more. • 1000+ installs • Compatible with iOS versions 8 - 10 • Optimized for iPhone, iPad & iPad Pro -- REVIEWS -- Gizmodo "Just mess around! Twiddle those faders! Swipe and click with reckless abandon! Turn the volume all the way up, give the dog a panic fit, and make your neighbours think the street's being invaded by giant cabbage people from planet Zok. Trust me, this will never get old.” Dangerous Minds “New online theremin simulator kind of sounds cooler than the real thing. Check it out and annoy your co-workers.” Mashable “Messing around with this virtual theremin is completely addicting” -- CONTACT -- To find out about my other musical app projects, please go to femurdesign.com and share your loops with me on Facebook and Twitter. Facebook: facebook.com/femurdesign Twitter: @femurdesign For any queries and support contact me here: femurdesign.com/support

Screenshots

Theremin I/O3 screens
Theremin Synth4 screens

Verdict

The call

The clearest difference is rating: Theremin I/O at 4.0 against Theremin Synth's 3.2. Theremin I/O also leads on review sentiment (77% vs 64%) and iOS requirement (8.0 vs 12.1). Theremin Synth's advantage is in-app purchases (none vs 1) and update cadence (every 2 months vs every 24 months). On price, ratings volume, ads 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

Theremin I/O costs $2.99 and Theremin Synth $2.99 up front. Theremin I/O sells 1 one-off in-app purchase. Theremin Synth asks for nothing beyond the download.

ReceptionRating · Positive reviews · Number of ratings

Theremin I/O holds the better App Store score, 4.0 against 3.2. Both are backed by a comparable volume of ratings — 5 and 6 respectively. Written reviews point the same way: 77% of Theremin I/O's written reviews are positive against 64% of Theremin Synth's.

UpkeepUpdate frequency

Theremin I/O ships an update every 24 months, Theremin Synth every 2 months. The most recent releases landed on November 6, 2026 and November 2, 2026 respectively.

Scorecard5 real differences · 5 level
Theremin I/O versus Theremin Synth: the parameters behind the verdict, then further details
ParameterTheremin I/OTheremin Synth
Price$2.99$2.99
Rating4.0 (5 ratings) — better3.2 (6 ratings)
Positive reviews76.9% of reviews — better63.6% of reviews
Number of ratings56 — better
Update frequencyEvery 24 monthsEvery 2 months — better
AdsNoNo
In-app purchasesYesNo — better
MonetizationPaidPaid
DevicesiPhone, iPodiPhone, iPad, iPod — better
Requires iOS8.0 — better12.1
Further details — not scored
Size18 MB1 MB
Age rating+44+
DeveloperFFFF00 Agents ABLuke Phillips

Customer experience

Theremin I/O

All ratings5 ratings
Positive60.0%
Neutral20.0%
Negative20.0%
Written reviews13 reviews
Positive76.9%
Neutral15.4%
Negative7.7%

Theremin Synth

All ratings6 ratings
Positive50.0%
Neutral0.0%
Negative50.0%
Written reviews11 reviews
Positive63.6%
Neutral0.0%
Negative36.4%

In-app purchases

1 purchases

Theremin I/O

One-time1
  • Network MIDI$5.99
None

Theremin Synth

No in-app purchases

Questions

Is Theremin I/O free?
Theremin I/O costs $2.99, and also offers in-app purchases.
Is Theremin Synth free?
Theremin Synth costs $2.99, with no in-app purchases.
Which has better reviews, Theremin I/O or Theremin Synth?
Theremin I/O is rated higher. Theremin I/O averages 4.0 out of 5 from 5 ratings, while Theremin Synth averages 3.2 from 6 ratings.
Do Theremin I/O or Theremin Synth have ads?
Neither Theremin I/O nor Theremin Synth shows ads.
Which is updated more often, Theremin I/O or Theremin Synth?
Theremin I/O ships an update every 24 months, and Theremin Synth every 2 months. Most recently, Theremin I/O was updated on November 6, 2026 and Theremin Synth on November 2, 2026.

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