KantoEditor

KantoEditor is a handy application that can perform various editing operations with MIDI, KAR and MP3 audio files, as well as convert them to other formats.
It offers a wide range of functions suited for editing and exporting karaoke songs, but features a rather outdated user interface.

Modify audio key, tempo or volume and remove tracks

KantoEditor supports a wide array of input formats, including MIDI, KAR, KFN and MP3. After loading an audio file, you can increase or decrease its key, tempo and volume, then select the desired output format. Additionally, the application can preserve the lyrics included in the source file.
You can view all the audio tracks contained in MIDI and KAR files, choose which of them should be included in the output songs, as well as adjust their individual volume. Moreover, you can modify the embedded instrument information for each channel.

Merge multiple audio files

KantoEditor enables you to join multiple songs into one large file. You can choose whether or not the lyrics should be saved in the output track, as well as add crossfade transition effects.
The application allows you to use drag and drop actions to add new files to the processing queue, but it is not possible to change their order once they have been loaded.

Lacks documentation and features an outdated interface

For the most part, KantoEditor is relatively easy-to-use, but it would help if the application included more thorough explanations for various functions and technical terms.
Also, visually, the program does not impress. The user interface looks quite dated and some of the text colors used in certain menus are very uninspired.
All in all, this is a useful application that can help you customize MIDI, KAR and MP3 files, convert them to other formats and merge multiple songs. However, its interface is not very well-designed and the program lacks adequate documentation.