This article describes how the sound is recorded from the digital keyboards used in the Musical Pieces videos. No microphones are needed when playing digital pianos.
Connecting equipment
An audio cable is connected between the output of the keyboard and line in on a computer soundcard.
OUTPUT from the Roland RD-700GX keyboard, right (R) and left (L) channel. The output has the form of two 6,35 mm jack sockets (TRS). In this case some jack to phono (RCA) adapters have been used before connecting a phono to mini jack cable between the instrument and the computer soundcard. The BALANCED OUT (XLR) at the right side might be used for mixers and other such gear.
Some keyboards only have the headphones jack to extract the audio from, for instance the Casio CDP-100.
The Yamaha P-140 has headphones jacks and dedicated AUX out phone jacks for audio recording. It turned out to result in less noise in the recording using the dedicated AUX out phone jacks.
Line in on a Soundblaster Live computer soundcard connected with the audio cables 3,5 mm miniature jack.
Other equipment than a computer soundcard installed in a stationary computer might be used as the recording devise. For instance a USB audio adapter connected to a laptop or a digital portable recorder with line in facility.
An example of a USB audio interface, the Steinberg CI1.
An example of a digital portable recorder with line in facility, the Yamaha Pocketrak C24.
Recording the audio
When the instrument and the recording equipment are connected it is time to record the sound. Some recording software is needed. In this example an old audio program named Cool Edit Pro is used.
To prevent distortion the sound level in the recording program should not be to high. To minimize unwanted noise the sound level should not be to low.
The sound level is set so that it does not exceed 0 dB (watching the red bars at the bottom of the picture).
It is an advantage to record the musical piece into a MIDI file first. Then play back the MIDI file while adjusting the volume of the instrument and the recording level in the computer so that it does not exceed 0 dB at any time during the piece. It is hard in advance to know how loud the sound will be. Being on the safe side recording at a low level might introduce more noise than necessary.
The sound is recorded, left and right channel.
The recorded sound level should now be adjusted so that the highest point in the sound curve reaches 0 dB giving the sound an even level from video to video.
In this software raising the sound level to a specified level is called Normalize.
The seperate sound file can now be combined with the seperate videofile in a video editing program. Turn the volume of the videofile completely down and place the sound file on the timeline so that it is in sync with the video file.
Recording a software piano
When using a software piano the audio is typically made from a recorded MIDI file. A piano MIDI file contains the data regarding what keys were pressed when and how hard and so on. The software piano program might have a feature like: "Mix down to MP3" or other format. This is then done in a digital way as fast as the computer can do it (as opposed to a traditional sound recording in real time as described above).
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Musical Pieces 
