PERCEPTUAL NOISE WEIGHTING
- Noise-weighting: shaping the spectrum to hide noise introduced
by imperfect analysis and modeling techniques (essential in speech
coding).
- Humans are sensitive to noise introduced in low-energy areas of
the spectrum.
- Humans tolerate more additive noise when it falls under high energy
areas the spectrum. The amount of noise tolerated is greater if
it is spectrally shaped to match perception.
- We can simulate this phenomena using "bandwidth-broadening":
- Simple Z-Transform interpretation:
which can be implemented by evaluating the Z-Transform around
a contour closer to the origin in the z-plane:
Hnw(z) = H(az).
Key points:
- Used in many speech compression systems
(Code Excited Linear Prediction).
- Analysis performed on bandwidth-broadened speech; synthesis
performed using normal speech. Effectively shapes noise to fall
under the formants.