Taming the OP-1’s line input digital noise

I think I’ve found a work around to minimize the digital noise when using the line input.

I mix in an inaudible (at least to me) high frequency signal (17 kHz sine wave) with the source I’m recording via a passive mixer.

I’ve generated the sine wave signal with Ableton Live’s Operator synthesizer; sequenced an 8 minutes long note; exported the audio file. I’m using either the computer or my iPod to play the signal. I set the volume as low as possible on the playback device.

The mixer is based on the Rolls MX41b but without the faders. It’s also similar to @darenager’s mixer. See the attached picture.

Here’s also an example with and without the high frequency signal.