Phase Cancellation: Vocals and instruments in a stereo mix often occupy the same frequency range, making it challenging to isolate and remove one without affecting the other. To mute a vocal part, you would need to find a way to cancel out the vocal frequencies while preserving the instrumental parts, which can be a complex and tedious process.
Spectral Subtraction: Another approach involves using spectral subtraction, where the vocal spectrum is estimated and subtracted from the full mix. However, this method can introduce noticeable artifacts, especially in dense and complex musical passages.
Multi-track Separation: If you have access to multi-track recordings of the song (i.e., separate vocal and instrumental tracks), removing the vocals would be much simpler. However, obtaining multi-tracks for copyrighted music is typically not straightforward, and they are not always available.
Here's a step-by-step process you could try in Audacity to attempt vocal reduction:
1. Import your heavy metal song into Audacity.
2. In the "Tracks" panel, select your stereo audio track.
3. Go to Effects > Vocal Remover to open the Vocal Remover tool.
4. Adjust the "Reduction" and "Smooth" parameters to reduce the vocal levels while minimizing artifacts.
5. Experiment with the "Frequency Range" settings to target the specific frequency range where the vocals are most prominent.
6. Use the "Preview" button to listen to the resulting instrumental track and make adjustments as necessary.
7. Click "OK" to apply the vocal reduction.
While Audacity's Vocal Remover can provide some level of vocal reduction, the effectiveness may vary depending on the complexity of the song and the characteristics of the vocals. Additionally, it's essential to note that completely eliminating vocals without audio artifacts may not be entirely achievable using this approach.