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I am a n00b in the field of electronic music production, as I have been played acoustic piano for years.

I am trying to connect my digital piano, a Kawai CN37, to guitar pedals.

I have the following setup:

Piano LINE OUT -> Guitar Pedal (boss DS-1/ Zoom gx1on) -> USB Audio Interface (Behringer 202HD) -> Piano LINE IN

So the idea is to use the piano speakers to emit sound.

The problem is that often I get a high pitch distorted sound even when I am not playing anything. This happens when the output is the piano speaker, but NOT when the output is the headphones. With the DS-1 I can get rid of it by adjusting the gain on the USB interface. However for the Zoom gx1on, I can't actually get rid of it , even with the lower gain setting.

My understanding is that it has to do with the level used by the different device. The piano uses a Line Level, the pedals are Inst, and I can change the level on the USB interface from Line to Inst. However, I couldn't manage to get rid of the ringing noise.

Any idea?

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Page 131 of the manual states:

Do not connect the LINE IN and LINE OUT jacks of the CN37 digital piano together with the same cable. An audio loop (oscillation sound) will occur, resulting in damage to the unit.

From that, my assumption is that the input from the line in is always mixed to the line out.

Although you're not literally using the same cable in your setup, it sounds like you're still creating a feedback loop as the piano 'hears' its own signal from the line in, and sends it out again through the line out.

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    Thank you for your answer, I doubt that's what happens. I would expect to hear a lot more noise, whereas I have that problem only with some pedal. I think it depends on the output level from the pedals/piano to the USB interface. I edited the question to be clearer.
    – Vaaal
    Commented Jul 25, 2019 at 12:07
  • @Vaaal I agree that you might expect to hear more feedback there was a feedback loop - but is it true that the line in of the piano is always sent to the line out? If so, then surely you must have a feedback loop. Do you get a different result if you plug headphones into the audio interface?
    – Нет войне
    Commented Jul 25, 2019 at 12:26
  • I believe that the line IN sends the signal to the speakers - but there is no connection from here to the line OUT again, so there is no loop. The line out sends the signal to the pedals and USB interface, but only the signal emitted when pressed the key - not the one capture by the speakers.
    – Vaaal
    Commented Jul 25, 2019 at 12:35
  • In the headphones the audio is better, I can hear that strange ringing tone only when the gain is really high, which again makes me think is something that has to do with the output level with some of the peals?
    – Vaaal
    Commented Jul 25, 2019 at 12:36
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    Can you try connecting a sound source to the line in of the piano, then connecting an amplifier to the line out, and seeing if you can hear the sound source? As I said in my answer, the manual strongly implies that the line in is mixed to the line out, which would give you a feedback loop.
    – Нет войне
    Commented Jul 25, 2019 at 12:55

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