User`s manual

4.4.12: Spectral Inverse Filter

Application:

The Spectral Inverse Filter (SIF) is an equalization filter which automatically readjusts the

spectrum to reduce noise and muffling effects. It is especially useful when the voice has been

exposed to reverberations and bandlimited noises. For an automatic implementation of the

SIF, use the ASIF (see Section 4.5.3: )

SIF measures the signal’s spectrum and uses this information to implement a high-resolution

digital filter for correcting spectral irregularities and reduce added noises. Figure 4-37

illustrates the process. The original audio spectrum (top trace) is inverted (middle trace). A

digital filter is implemented which has the shape of this middle trace. When the original

spectrum (top trace) is modified by this filter, low energy frequencies are boosted and high

energy frequencies are attenuated. The resulting “filtered” audio has a flat spectrum.

This mode of operation is called Equalize Voice. Available controls permit the operator to

reshape the output audio to flat, pink, voice-like, or custom spectrum. The operator also

specifies the spectral range to be equalized using upper and lower frequency limits; audio

outside these limits is attenuated. The amount of spectral correction is adjustable using the

Filter Amount control.

Figure 4-37 Basic Process of Spectral Inverse Filter