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I'm trying to figure out how to record my Roland FP-30 digital piano.

I have a Focusrite Scarlett Solo (2nd Gen), which has only one instrument/line input (I assume it's a balanced mono input, but then again how is it different from an unbalanced stereo since they both have 1 tip + 2 rings?)

Since the FP-30 doesn't have dedicated line outs, I can't use its L/Mono channel to connect to the interface in mono. So I have to use a headphone out for that purpose.

I'd like to know if it's okay to connect an unbalanced stereo signal to a balanced mono and what cable should I use for that?

A regular TRS to TRS stereo cable? A stereo TRS to mono TS cable (though I'm not sure it's going to be any different from using a regular stereo cable)? A stereo TRS to two mono TS splitter (and connect only left channel to the interface)? Will there be any difference between these cables?

I'm asking all that because I heard that it's not safe to connect a stereo output to a mono input without a dedicated adapter that utilizes resistors to prevent back-feeding (have no idea what that adapter is), otherwise there could be damage. It's also good to know these things to avoid problems down the road.

I was also thinking about connecting directly to my laptop's Mic in port (also mono), will it be any better/worse than using my Focusrite Scarlett Solo?

Thanks a lot in advance!

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  • 1
    Not quite a duplicate, but answer is the same: music.stackexchange.com/questions/85939/…
    – Your Uncle Bob
    Commented Jul 5, 2019 at 12:21
  • Yeah, except that his audio interface has two line inputs, while mine has only one. My digital piano, on the other hand, has stereo recorded piano sound. Thanks for pointing to that post anyway, since I now know that a regular stereo cable will not work since the input of my interface expects a balanced mono signal. So the question is whether it's better to use a stereo TRS to TS mono cable, or stereo to two mono TS splitter and connect only TS end? Also, not sure about my laptop, which most likely has an unbalanced mono, so doesn't expect balanced signal. Will stereo cable do in that case?
    – MikeRoss
    Commented Jul 5, 2019 at 12:57
  • Also, would be great to hear overall thoughts on how "safe" either of these setups is going to be as well as how much the audio quality is going to suffer except for obviously downgrading from stereo to mono sound?
    – MikeRoss
    Commented Jul 5, 2019 at 12:58

2 Answers 2

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Stereo TRS is very different from balanced TRS. You should not use a TRS to TRS cable. It will lead to ugly phasing effects.

The TRS connector in the piano is really only meant to drive stereo headphones. However, it is common to use it as stereo line out. Connecting the left and right signal will force the built in headphone amp to produce a mono mix. It will probably just work, but it is not intended for that.

The TRS connector in the sound interface will be engineered to accept both balanced and unbalanced (mono) signals.

So... Here are your options:

  1. Get a stereo audio interface
  2. Connect with the USB connector (as a midi controller) and use piano sounds from your computer.
  3. Check if your piano has mono sounds (it usually does). Then get a stereo jack to 2 mono jack cable, and connect only one of them with the audio interface.
  4. Just connect with a mono jack cable. It does effectively the same as Your Uncle Bobs suggested custom cable. But note that the headphone plug (and its amp) were not designed for that.
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  • Note that using a mono cable will result in a 6dB higher noise floor than using a pseudo-balanced cable. But when recording modern equipment that may be less of a concern than when recording vintage analog synths.
    – Your Uncle Bob
    Commented Aug 5, 2019 at 13:57
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An external USB audio interface will always deliver much better quality that the built-in audio chip in your laptop, so I would definitely try to record the piano that way.

While connecting a headphone output to a line input is not ideal compared to using an actual line-level output, it should work and will not damage anything. Make sure the audio interface is in line-level mode, and not in microphone or Hi-Z guitar mode. Combining the two channels of a stereo output on modern equipment is also unproblematic.

I'd suggest you make a pseudo-balanced cable with two TRS jacks, with at the piano side: wire 1 connected to Tip+Ring, wire 2 connected to Sleeve, cable screen unconnected, and at the interface side: wire 1 connected to Tip, wire 2 to Ring and cable screen to Sleeve.

INSTRUMENT                     INTERFACE

   Tip +
       |
  Ring +---------wire 1---------- Tip

Sleeve ----------wire 2---------- Ring

       ----------screen---------- Sleeve

Then mark the jacks as input and output, so that you don't accidentally connect it the wrong way round. (You would notice immediately, though. One output channel would be connected to both Tip and Ring at the interface side, so you'd get no sound.)

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