GUIDE · EP-133 K.O. II
HOW TO RECORD
YOUR EP-133
ON iPHONE.
Since OS 2.5 the K.O. II is a class-compliant USB audio device. That means one USB-C cable from the sampler to the phone, no interface in between, and every pass you play becomes a take.
LAST UPDATED 1 OCTOBER 2026
What you need
That is the whole list. No audio interface, no adapter and no laptop. Firmware before 2.5 did not send audio over USB at all, which is why older guides run the headphone output through an interface. On 2.5 you no longer need to.
Seven steps, most of them short
Getting a good take
Levels
Do not fuss over them. The record path is 32-bit float, so a loud pass has no ceiling to clip against on the way into the phone. GAIN in REK. moves what you hear by ±12 dB and leaves the file alone. If the PK lamp lights, it latches so you know a peak happened; the take is still intact.
The one thing 32-bit float cannot fix is distortion that happens before the cable. If the K.O. II’s own master is clipping, that is in the audio it sends. Keep the sampler out of the red and let REK. worry about the rest.
Hearing what you play
Monitoring is AUTO, ON or OFF. AUTO steps aside when you play a take back. If you would rather listen on the K.O. II’s own headphone output, set monitoring to OFF and the phone stays quiet while it records.
Counting in
The metronome can give you one or two bars before recording starts, anywhere from 40 to 240 BPM. Set it to the K.O. II’s tempo, or leave it OFF and start on the pattern.
Long sets
The free version records one minute per take, which is enough to prove the setup works. One payment of $9.99 lifts the limit for good. Takes stream from disk, so an hour plays back as easily as a minute, and low storage warns rather than refuses.
When it does not work
The EP-133 does not show up as an input
The usual cause is firmware older than OS 2.5, which does not send audio over USB at all. After that, check that the cable carries data and not only power, then unplug and reconnect with REK. open.
My K.O. II is on older firmware and I cannot update it
Run the K.O. II’s headphone output into any class-compliant USB-C audio interface. REK. takes the interface as an ordinary input, and everything else in this guide applies unchanged. The USB audio guide covers that route.
The take sounds distorted
If the PK lamp lit but the take sounds clean, nothing was lost: REK. records in 32-bit float, so there is no clipping ceiling on the way in. If you can hear the distortion on the K.O. II itself, it is happening inside the sampler before the audio reaches the cable. Bring its master down.
Can I record each group to its own track?
No. REK. records the stereo pass as one take. There is no multitrack, no stems and no overdub; a pass always makes a new take.
Does it work on iPad or Android?
No. REK. is an iPhone app, sized for one hand and one thumb.
Other guides
- A synth recorder for iPhone
- How to record Digitakt performances on iPhone
- Record your groovebox without a DAW
- USB audio recording on iPhone
- Something else wrong? Support has the common situations and a human on the other end.
START
RECORDING.
Plug in the K.O. II, open the app, press the red one. There is nothing to set up first.
$9.99unlimited recording
Free1 minute per take