How to improve recording signal quality/reduce noise?

Question

I have an electric keyboard which has pretty good-sounding output. It has two headphone jacks which provide the same output which sounds good with my headphones. I wanted to record the output so I got this male-to-male audio cable and connected one of the jacks to the red jack in my computer's sound card. I managed to set it up and get a recording, but the result is quite noisy: see here for an example. Essentially there's a lot of background noise, and that's after I applied the noise reduction in WavePad. (Here is the pre-noise-reduction one.)

How do I get the recording to have less noise in it? There is no noise if I plug my headphones directly into the jack and I'd like the recorded output to be the same.

Additional details as requested: I'm using the Yamaha P65. I'm using one of the 2 mini headphone jacks (3.5mm) as output. The soundcard model is the built-in soundcard for my motherboard whose model number escapes me, yet I will find a way to look it up if needed. The input socket is also 3.5mm audio input.

Answer 1

The point is that the headphone output on your keyboard is stereo, your soundcard's input is mono. So the noise is very likely caused by the fact that the input of a mainboard is designed for microphones and carries supply voltage on the pin that would be used for the right audio channel on a headphone jack.

There are 3 possible solutions:

1) Use the line output of your keyboard instead (if it has one)

2) Use an external audio interface that can deal with stereo signals

3) Use a 3.5mm stereo -> 2x 3.5mm mono cable and leave one of the mono ends disconnected

EDIT:

4) (probably the best) Use the blue Line-In jack as it is designed for handling stereo signals. If your keyboard has a Line-Out jack, use it instead of the headphone jack to feed the Line-In as the levels are different.

After I heard your samples again (not in the train this time), the problem became quite obvious: use the same power outlet for your keyboard and your computer, that should deal with the 50/60 Hz noise floor. The high frequency hiss may be a result of your sound card acting strange as result of that.