Turn your iPhone or iPad into a musical instrument! RD4 - Groovebox is a music making app with virtual analog synthesizers, drum machines and effects.

Compose and arrange your music in real-time. Choose instruments individually for the 4 channels. Record live or set notes with the dedicated sequencer or piano roll of each instrument.

"This is no desktop app crammed onto a touchscreen. It seems the interface has been designed around your fingertips." Peter Kirn from CDM (

Via in-app purchase: Upgrade to premium and unlock the following features:
Save Song, Export Loop, Audio Session Recording, Share Sounds, All 10 Drum Kits, All 5 Effects, Mixer Instrument Configuration, Effect Bus Configuration, MIDI Input and MIDI Clock Sync in/out.

This multi-touch enabled app makes it simple to invent unique loops and musical phrases. Manipulate the sound of the synthesizers by tweaking the oscillators, resonant filters and audio envelopes. Add audio effects like reverb, distortion, phaser, filter and delay to your sounds.

Appropriate both for experienced musicians and beginners.

Feature Overview

- 4 channel rack mixer
- Instrument selection for each channel
- Volume control with level meter per channel
- Direct audio effect channel assignment
- Tempo control with tap tempo
- Channel mute and solo

- 2 banks with up two 8 bars per instrument
- Adjustable play modes from 1 to 8 bars and random modes
- Song Mode with a length of up to 99 bars

Choose between two virtual analog synthesizers and the drum machine for each channel:

- Modeled after legendary monophonic synths of the '70s
- For fat sounding bass and powerful lead sounds
- 3 oscillators with 6 different waveforms
- Each oscillator can be tuned precisely and has a warmth control for the typical analog sound
- Attack, Decay, Sustain and Release envelope generator
- Pitch wheel
- Low-pass filter (24dB/oct, 4-pole) with knobs for cutoff, resonance and an Attack/Decay/Sustain envelope generator

- Recording of played notes in real-time
- Piano Roll for editing recorded notes comfortably
- Or compose by drawing notes directly with the piano roll in 1/16 or 1/32 resolution
- Piano roll editing features: Transpose Pattern, Shift Sequence and Quantize Pattern

- Reminiscent of the legendary 303 synthesizer
- Create bubbling basslines and screaming lead sounds
- Successor of the famous synthesizer Rubberduck from d-lusion
- High-quality low-pass filter with resonance, cut-off, and envelope controls
- Oscillator with 4 types of waveforms
- Real-time step sequencer with accent and slide

- Program beats with 10 classic drum kits: 808, 909, 606, CR-78, Linn, KR55, RX11, RZ1, DMX, DPM48
- Booming kick drums, snappy snares and throbbing percussions
- 8 channels per drum kit
- Punch control for volume and envelope adjustments
- Accent programmable for each drum channel
- Free assignable effects for each drum sound
- Channel mute, Closed Hi Hat mutes the Open Hi Hat
- Real-time pattern based step sequencer

Audio effects:
- 5 effects: Reverb, distortion, filter, phaser and delay
- Real-time controllable
- X/Y control field for each effect
- 4 effect sends
- Chaining of 2 effects

Technical features:
- Audiobus support
- Core MIDI support
- Connects to all available MIDI input sources automatically
- MIDI Clock Sync support, in/out
- Automatic MIDI input focus when switching Instruments
- Multi-touch control
- Live session recording
- Audio loop export feature
- Session save capability
- Cut/copy/paste pattern

What’s New

Version 2.3.8

- broken in-app purchase fixed

Ratings and Reviews

3.4 out of 5
8 Ratings

8 Ratings

Djbombsquad ,

Enticing interface but lacking basic features

I got this app cuz it's the only 303 emulator I've seen that has standard piano keys instead of notes for the step sequencer, nice implementation and design.

Sadly there's only three instruments: one synth plus a 303 and a drum machine. You can assign any one you want to the four tracks in any order, ie 3 drum machines plus one synth or 4 tracks of 303 if you want.

The sound quality is ok at best, the main synth very boring sounding and not very tunable even with 3 oscillators. The 303 and drum machines are just as lacking in tuneablity. As for the drum kits they give you "punch" knob instead of a volume knob per instrument that doesn't really change anything.

The worst part is the piano roll or grid mode is only for the analog synth why not every instrument? I went of the pictures in the store.

No audio copy/paste - useless
No advanced midi features
Laggy note input with keys on real time recording
Too expensive

Layout and Design
Multiple 303s, easy to program

All in all: at the moment this is not a very inspiring music app with a few tweaks could be great. If you want something better and cheaper, I recommend Xenon, 5 tracks and grid sequencer for every instrument and they are all extremely tune-able just like real hardware.

Good luck mikrosonic

whocaresatthispoint ,

Longest "Bait and Switch" Scheme Ever Run In App Store

Run from this app. The slim version is no longer worth the few seconds it takes to download.

I've loved this app and have been using it regularly for a very long time—previously had my review at four stars—until this afternoon, when an automatic update removed all but one of its drum kits and many of its other features.

Tapping restore does nothing to restore any of the elements I've been using without a problem for the entire time I've been using the app.

I'm not sure why the developers felt it necessary to utterly neuter, and thus eliminate the possibility of enjoying, the user experience, but for anyone in the market for an app that's a versatile groovebox, drum machine, synth, etc., and you've heard good things about this one, ignore what you've heard.

More important, though, can you really trust developers who decide without warning to take away features you've had and have been using for years in order to engage in a scheme to begin charging for them?

In my view, absolutely not.

anickt ,


UPDATE - still worth 5 stars to me. Great for acidic loops. Easy export to AudioShare. Still like it!

I'm giving it 5 stars right away because I found it so intuitive and easy to get some interesting results from. Compared to other similar apps it just seemed to click for me. I bought the IAP pretty quickly after trying it out. There's plenty more to explore but I'm already sold. I think they did a good job with this so far.

App Privacy

The developer, mikrosonic, has not provided details about its privacy practices and handling of data to Apple.

No Details Provided

The developer will be required to provide privacy details when they submit their next app update.


  • Family Sharing

    With Family Sharing set up, up to six family members can use this app.

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