Recording a Keyboard in Stereo

I’d consider myself a fairly novice audacity user and quite new to audio recording in general. Regardless, I’m currently in the process of recording a song comprised of vocals and piano. I have a keyboard and a mic both hooked up to an audio interface (Scarlett 2i4) that connects to my computer via USB. Both devices are connected to one of those XLR/ TRS combo inputs; the mic using XLR and the keyboard using a single 6.35mm cable (since there is only one output on the keyboard). Typically the mic will record to the left channel and the keyboard to the right which has always been fine. But for this particular song I’d wanted to record the keyboard in stereo as to make the mono vocals more pronounced.
I’d resigned myself to this not being possible without splitting the audio from the keyboard and using up two inputs; one to record left and the other to record right. That is until by some strange fluke I began recording some keyboard playing and noticed it was recording in stereo. The resulting two channels were distinct (they weren’t just identical waves) and the mic was off so it wasn’t just the microphone recording the playback from the speakers - plus I’d like to think I’d have noticed if it were that.
I then turned the mic on to test what the vocals would sound like over a stereo instrumental and it did indeed sound much better than having the vocals and keyboard both mono. However upon turning on the mic I lost the ability to record the keyboard in stereo and have since been unable to recreate whatever conditions made it work.
Basically what I’d like to know is if it’s at all possible to record a keyboard in stereo using a single 6.35 lead into the XLR/TRS port of an audio interface. My one-off freak recording would lead me to believe it is but I’m willing to concede that I’m actually crazy and somehow mistaken. Also, if it’s not possible, would using some sort of splitter allow me to record the left and right channels independently or would that simply result in two mono recordings.

Hope that makes some kind of sense. Thanks, Aaron.

Up until right there I would have flat said, forget it. The device is aggressively two channel and there’s no end of people complaining about the microphone only showing up on Left or Right depending on where they plugged it in.

It’s not a “stereo” device. It’s two channel.

However, I’m spilling coffee trying to think of a way you would get your effect or result.

You picked the headphone output of the keyboard, right? That’s how I do it. I don’t have a “Stereo Line” connection, either. The difference is I go into a stereo mixer and have full control over what goes where.

Did you connect the system with a stereo 1/4" cable? Does the plug have two black bands or only one (attached-2)?

So it’s stereo (tip=left, ring=right, sleeve is ground) inside the 2i4. Now it gets fuzzy. What does the 2i4 do with the right channel if you unplug the XLR?

We know that the 2i4 switches between line and microphone level (XLR/1/4") when you plug something in. There is no button. It just knows. If you plug in an XLR, chances are terrific you have just supplied a microphone. If you plug in a 1/4", it’s a choice between Line level or slightly lower instrument level and there’s a switch for that. I know of no provision for swapping between the two channels, but that doesn’t mean there isn’t one.

I should dig in the instructions.

You can do some experiments. Plug a stereo 1/4" cable (two black bands) in the left input and nothing at all in the right. Set both for Instrument. Hold the other end of the cable with a towel so your hand doesn’t touch the connector. Get something all metal like a paper clip or fork and touch first the tip of the connector and then the ring between the two black bands. This is a quick and dirty way to see if there is signal down the cable. If you start recording in Audacity, it should buzz certainly when you touch the tip, but might also buzz on the other side if you touch the ring.

It’s a little more complicated version of doing this:

I’m going to go find the instructions.

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I then turned the mic on to test what the vocals would sound like over a stereo instrumental and it did indeed sound much better than having the vocals and keyboard both mono. However upon turning on the mic I lost the ability to record the keyboard in stereo and have since been unable to recreate whatever conditions made it work.

How do you know it sounded much better? Listening to the 2i4?
What’s the mic?


There are various ways to produce a fake stereo effect from a mono original.
e.g. Duplicate the mono track, apply different different equalization to the original and duplicate : one track favouring bass , the other biased towards treble. Then make a stereo track of these two differently equalized tracks : voila pseudo-stereo.

[ Steve’s pseudo-stereo plugin produces a different faux-stereo effect : it has reverb]

Creating a dual-mono track , ( which looks like stereo but tracks are absolutely identical) , then shifting the tracks out of sync by a fraction of a millisecond , creates a wide-stereo effect. So accidentally adding such a delay to one track will produce a wide-stereo effect.

Thank you for the reply. It is a stereo 1/4" that I’m using also the mic is a Rode NT1-A. Incidentally the keyboard is a Yamaha NP-30 and, your right, i’m just using the headphone output.

I tried that little experiment multiple ways and the 2i4 consistently responded to both the tip and the ring of the jack being touched. However the response was outputted to a single channel, as you might suspect. It recorded to a single channel in audacity and panning my speakers left and right didn’t isolate the buzz from either part of the jack (my 2i4 runs into a separate amplifier that has a left/rial dial). I suppose that narrows the culprit down to the 2i4. Presumably it ‘mono-tises’ the stereo input. I’ve always thought that the 2i4 wasn’t capable of outputting in stereo it’s only that I was so convinced that audacity had somehow captured stereo audio from the keyboard. Obviously I was too elated to bother saving the file as evidence.
I listened to the recording afterwards, through headphones connected to my computer. The keyboard sounded as it would if headphones were connected directly into it, in the sense that there was a slight difference between the left and right channels; presumably the result of the keyboard trying to replicate the natural asymmetry of an actual piano. This distinct stereo recording just helped separate it from the plainly mono vocals; it’s quite a common mixing practice from what I understand, which is admittedly very little.
Assuming I am crazy and mistaken about the recording, and assuming the 2i4 does reduce all signals down to a mono output, perhaps something like the adapter pictured below would work. Presumably it separates the signal into a left and right output and I could simply plug both into the 2i4. It wouldn’t leave any room for a mic but I could live with that.

But again thank you for the reply. It’s quite late where I am so I’m off to bed for the time being. Thanks, Aaron.

Yeah, I think I’ll probably end up doing something like that. I can’t imagine it’s all that different from the sound that the keyboard is actually outputting. Thanks for the tip.

The computer thinks it’s a stereo device. It has a real left and a real right, but you have no tools at the 2i4 to do anything between the two channels. What you plug into the left connection goes to the left channel of the stereo show. Full Stop. The mono, button, by the way is for monitoring. I don’t think it actually does anything to the show.

It’s not dreadful that you can’t record the microphone and stereo piano at once. You can create a finished vocal mix performance through overdubbing. Record the piano and then play it into your headphones and sing into the microphone. Audacity will make a second track with voice only. Mix and edit as needed.

I don’t recommend this, but the simplest thing to do when you lay down the vocal track is split the half stereo track and convert it to mono. Then export the show. Audacity will mix down your voice to the center of the stereo piano.

There’s no doubt you’re going to want to do production, filtering, timing ,etc, etc, so that wouldn’t work for desirable production, but it electrically does work.


I don’t think that cable is going to work. I think it’s just a simple “Y” cable. Put one mono show into two places. The product description has to say “Stereo Splitter” and the plugs should be marked somehow Left and Right.


Yes I think some sort of splitter cable would be the best option. I rarely have a need to record vocals and piano simultaneously anyway so it’s a minor grievance. In the instances that I do I’ll try adding some stereo effects in post as Trebor kindly suggested.

Thanks again for the help. Aaron.