Best free audio editors to remove or minimize the vocals of a song

In Ocenaudio go to Effects > Equalization. Bring to 0db the equalizer in the range of 250 to 1k. Preview until you find the perfect setting. Apply this setting and save the song.

Audacity will give you also the option to remove vocals from songs in batch mode. Go to Effects, and click to activate Vocal Remover. Save the processed file.

In WavePad go to Effects and click Reduce Vocals. Set Pan position, Vocal Level, etc., preview the song and save it in the format you prefer.

In Wavosaur go to Process and select the Vocal Remover option. The sound editor automatically processes the song and minimizes the vocals.

If you prefer to remove the vocals without encoding audio files in an editor, you can do it on the fly.