A creative bass synth sequencer for creating electro melodies or dirty phat & funky acid techno basslines.
Inspired by the acid house music scene. An IOS exclusive, compared to a modern equivalent to Rebirth (Rebirth was a popular tb - 303 clone a decade ago).
Look at the video tutorial for a how-to guide. Listen to what you can create easily with 2XB303.
Create synth sequences using standard step functions as seen on various sequencers like the Roland SH 101 synthesizer or sequences can be generated randomly.
Easily capture whatever you hear and export to AudioShare, Audio-Copy, Email or iTunes Shared Folder
Tweaking cut-off & decay Env-Mod & glide & accent etc for that classic sweet-spot acid growl Tap to dials to swipe up & down for fine adjustment of knobs.

The sound was first compared to a Cyclone TT - 303 & tweaked to extend sound shaping beyond a just bass maker. Waves have optional harmonic version, noise, LFO, glide speed & PHAT/ BASS, and great effects. This is designed to give more creativity beyond an acid synth bass maker.

Use the keyboard for the following cool tricks:
[Sequence/Control/Transpose]: Transpose both channels simultaneously while playing.
[Sequence/Control/Pattern]: Instantly switch to a saved sequence while playing. Keys correspond to stored program numbers, starting from the current program thats loaded (key 1 is your current program, key 2 is current program+1). Highlighted keys show stored programs. This is great for building up live tracks, or instant crossfading between programs. You can also "Hold settings" so it locks settings like effects.

METRONOME: Toggle drum beats -better than tick-tocks to accompany your bass lines

LFO auto control low pass CUT-OFF and/or PITCH. The pitch level can give a vintage effect subtly detuning with low SPEED or faster for chaotic random pitches.

EFFECTS (Global/master are in yellow.)
OVERDRIVE, COMPRESSION adjusts threshold, ratio, & gain. This is a global effect.
ECHO tempo synced with feedback & wetness.
SAVE ALL. When not playing, save to memory.

Ableton Link syncs with apps .Enable for precise timing without syncing. Press LINK button at the bottom for settings.
MIDI sync with External, Virtual or Audiobus. 2XB303 can be master or slave. ( any simple class-compliant USB should work but some may need to be power assisted)
Virtual MIDI In is always on. If you send from another app AND receive MIDI clock then you will be receiving both MIDI CLOCKS. Choose only one unless you want double tempo (which can be interesting).
While Ableton Link is enabled you can send clock. This means you can use one app to control 2XB303 with external hardware
MIDI note data is sent out on each channel

Record a fixed length, default to 32 steps. Can be changed in settings.
Arming the sampling with CAPTURE (flashing). Starts at counter 1 (ON).
PLAY CAP to listen to your sample loop.
Audio can be routed via IAA into apps like Apple's Garageband. Garageband will also sync your sequence for excellent multi-track recording.
Audiobus 3. Route audio to mix or record into other applications

To save you press "Save all", it then flashes. Now choose destination ("!" means its occupied ) then press "Save All" to confirm.

What’s New

Version 1.9

Fixed the swing/shuffle effect:
This never quite worked well as it sometimes cancelled out some glide notes.
Finally, this has now be rewritten so it just works.
Now you can get those groovy shuffle swing patterns.
Swing amount is a global setting found in the main sequencer/sequence menu. This also affects the backing beats.

Ratings and Reviews

Guycoolio ,

Really Nice 303

One of the best Roland 303 bass line synths I have heard on iOS. I like it better than Troublemaker and Bass Line. In its current state it is as authentic sounding as Syntronik’s 303 emulation, Rebirth 338 and Retronyms’ TT-303. It would be a go to app with AUv3 in my opinion. Works fine in AUM using IAA and syncs to tempo thanks to Abelton Link. Has decent effects (echo, distortion, and compression/ducking) that provide an old school vibe and a musically useful signal boost. Filter section is nice and it has midi capability. You can also capture the audio and send to AudioShare.

Sequencer is easy to use. The generate sequence feature is good and allows the user to pick the notes used. GUI is functional but further development for the entire app is welcomed. For the price, it is a no brainer to down load if you are a fan of this kind of sound. Honestly, you would have to purchase hardware in order to do better. Kudos to the developer.

anickt ,

Fun but...

I know the dev is working on updating this app. I brought up the knobs earlier but let me make it clear this is one funky app with lots of cool sounds coming out of it!

PREVIOUS REVIEW: The knobs need work. They shouldn’t move as soon as you touch them. They also should have a little “friction”. They turn too easily. The best knobs in iOS let you tap on the knob and then move away from center to better see what you’re doing and to make finer movements. Since a lot of 303-ism is tweaking, this is the main area that needs to be addressed. I like it otherwise.

Developer Response ,

Thank you for the review.
I hope you like the update with new dial-assist where you can enter a fine tune mode if you tap the dial

Zztoupe ,

Bluetooth enabled?

Enjoying the the app very much. I do to want use it with Bluetooth speakers but can’t connect. Please advise me to enable this function. Keep up the good work.

Developer Response ,

Hi thanks for the rating and feedback. As far as I know audio should perform normally as Apple should automatically route to Bluetooth but you might have to look at your IOS audio settings on device as sometimes they have alternative routing options IE built in speakers , ear piece etc. All depends what device and OS. I will have a look myself very soon to see if I can get them to work or find any issue. Thanks for the stars much appreciated. Email me at


Rob Wilmot
10.7 MB
Requires iOS 9.3 or later. Compatible with iPhone, iPad, and iPod touch.
Age Rating
Rated 4+


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