OB vs RX
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
OB
This app emulates the classic Oberheim OB-X synthesizer, offering its rich sound and behavior with added enhancements. It focuses on sonic quality and includes micro random detuning for authentic analog warmth. External effects are recommended to further shape its versatile soundscapes.
- Oberheim OB-X emulation
- Recreates original sound and behavior
- Added enhancements to original design
- Micro random detuning
- Rich and good sound quality
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OB-Xd is based on the Oberheim OB-X. It attempts to recreate its sound and behavior, but as the original was very limited in some important ways, a number of things were added or altered to the original design. OB-Xd was designed to sound as good and as rich as the original. It implements micro random detuning. Also, like many synths of the OB-X's generation, the OB-Xd has no internal effects so its sounds and textures can be greatly enhanced by the use of additional processing like chorus, reverb, delay, etc.
RX
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Play the wind synth you know with a whole new set of sounds. Warm woodwind tones for a soft ballad, bright synth leads for a bold solo. RX-79 is a breath synthesizer that turns your wind controller and iPhone or iPad into a full sound module. Saxophonist SJsax shaped every sound and every response by actually playing it. [Find the right sound for every song] 41 built-in sounds. 14 acoustic sounds including soprano, alto and baritone sax, clarinet, oboe, flute, trumpet, euphonium and harmonica, and 27 electric sounds including brass, leads and basses. Play the same melody in many different moods. Tap the preview button in the sound list to hear a sound even without a controller. [Fit it to your breath] Adjust breath sensitivity, response curve, attack and decay, and set breath noise, tonguing and note-to-note connection to match your playing style. [Make it your own] Shape each sound with brightness, resonance, drive, vibrato, delay and reverb. Save the settings you like to the USER list and give them names. Saved sounds stay on this device. [SJ PACK: 10 signature sounds, sold separately] Extra sounds that carry SJsax's playing feel. Before buying, you can play each sound yourself for 30 seconds. Note: SJ PACK is an in-app purchase sold separately from the app (one-time purchase). [Connection] Connect a USB MIDI wind controller. RX-79 responds to breath (CC2, CC11, aftertouch), pitch bend and vibrato (CC1). Depending on the ports and power needs of your controller and iPhone or iPad, you may need a separate cable or adapter, such as a USB camera adapter. Sound plays even with the silent switch on, and you can play along with backing tracks from other apps. No internet connection required. No personal data is collected. Connection and support https://sjsax.com/rx79/
Screenshots
Verdict
The clearest difference is in-app purchases: OB at none against RX's 1. OB also leads on chart position (#199 vs unranked). RX's advantage is update cadence (weekly vs every 2 months) and price ($9.99 vs $14.99). On ads, device support and iOS requirement 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
OB costs $14.99 and RX $9.99 up front. RX sells 1 one-off in-app purchase. OB asks for nothing beyond the download.
OB ships an update every 2 months, RX weekly. Both last shipped on October 29, 2026.
| Parameter | OB | RX |
|---|---|---|
| Price | $14.99 | $9.99 — better |
| Rating | 4.3 (64 ratings) — better | — |
| Positive reviews | 57.0% of reviews | — |
| Number of ratings | 64 — better | — |
| Update frequency | Every 2 months | Weekly — better |
| Ads | No | No |
| In-app purchases | No — better | Yes |
| Monetization | Free | — |
| Best chart rank | #199 — better | — |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Requires iOS | 15.0 | 15.0 |
| Further details — not scored | ||
| Size | 25 MB | 25 MB |
| Age rating | 4+ | 4+ |
| Developer | DiscoDSP LLC | sung ju KIM |
Bugs and requests
OB
Reported bugs
13 issues- Crashes in Audiobus
- Cannot use in MIDI section of Audiobus
- Preset browser issues (scrolling, cut off banks)
- Automation bug with cutoff freq
- UI issues on iPad Pro (buttons misaligned, text cut off)
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- App suspends on iOS 14
- No virtual keyboard in standalone app
- AUv3 crashes when adding second instance
- UI messed up in AU
- Knobs don't line up with display
- Wonky controls
- Programmer page without menu, cannot save/open patches
- LFOing filter cutoff jerky
Requested features
19 requests- Add last/high priority for mono patches
- Increase polyphony to 8 voices
- MIDI Learn functionality
- Preset browser improvements (categories, scrolling)
- Adjustable keyboard size
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- GUI scaling/layout redesign for iPhone
- Skins for GUI
- MIDI keyboard in standalone mode
- Effects
- Preset manager
- Zoom functionality for AUv3 on iPhone
- Fix knob turning bugs
- Add patch select in DAW apps
- GUI color scheme options
- Manual in settings
- Import presets
- Layering sounds (like original OBXa)
- White pinstripes on blue background (cosmetic)
- Mod wheel customization
RX
Not enough reviews yet to summarise bugs or requests.
In-app purchases
OB
No in-app purchases
RX
- SJ PACK$5.99









