This paper demonstrates the superiority of energy-based features derived from the knowledge of predominant-pitch, for singing voice detection in polyphonic music over commonly used spectral features. However, such energy-based features tend to misclassify loud, pitched instruments. To provide robustness to such accompaniment we exploit the relative instability of the pitch contour of the singing voice by attenuating harmonic spectral content belonging to stable-pitch instruments, using sinusoidal modeling. The obtained feature shows high classification accuracy when applied to north Indian classical music data and is also found suitable for automatic detection of vocal-instrumental boundaries required for smoothing the frame-level classifier decisions.