1. Voice Removal from Music
Benjamas Panomruttanarug and Adam Berenzweig
Final Project for EE4810 DSP
Prof. Dan Ellis

2. Introduction What? Why? How? Remove singing from music Karaoke
Research tool
How?
Stereo center channel subtraction
Enhancements to reduce side effects

3. Stereo Two ears, two channels. Audio Perception
Spatialization
IID, ITD
Audio Engineering Techniques
“Stereo Field”, Panning
Record voice mono
Voice usually panned center
Exceptions: stereo reverb, vocal doubling, etc.
voice bass
guitar
hi-hat

4. Overview of Experiments
sound output
Simple method
spectrogram
sound output
Filter_yui method
Original sound
spectrogram
Filter_adam method
sound output
sound output
Mask method
sound output
sound output

5. Phase Reversal or Center-channel Subtraction
Cheap trick:
Signal panned center contributes equally to L and R.
Phase-reverse R (180º) and add to L is equivalent to subtraction.
L(t) = .5 x1(t) + .8 x2(t)
R(t) = .5 x1(t) + .2 x2(t)
--> L(t)-R(t) = .6 x2(t)

6. Side Effects Doesn’t work if voice not centered. Stereo is lost.
Stereo Reverb
Where’s the Beef? Lost bass.
Other strangeness

7. Restoring Stereo: Phase decorrelation
Auditory system uses phase for localization
correlated phase may be used to attribute multiple reflections to the same sound source
precedence effect
Decorrelating phase tricks auditory system into “externalizing” sound.

8. Simple Filtering to Reduce Side Effects
Only perform center-channel subtraction on frequencies where voice is present.
Some stereo restored
original
plain ccs

9. Masking Method Selectively filter in frequency and time.
Combine masked |STFT| of L-R with original |STFT|.
Preserve original phase.

10. Determining the Mask Crude heuristic: three thresholds
Absolute magnitude (in voiceband)
|L|
Magnitude difference
|L| - |L-R|
Phase difference
angle(L) - angle(R)

11. Future Work Better mask? Time-domain segmentation first
Source separation… very hard.
Time-domain segmentation first
Machine learning techniques
Adaptive optimal threshold determination?
Current heuristic method has too many parameters to tweak.

12. References
Kendall, G. “The Decorrelation of Audio Signals and Its Impact on Spatial Imagery”. Computer Music Journal, 19:4 Winter 1995.
Erik Larsen, Philips. Private Communication.