RASTA filtering and mean subtraction was introduced to support
perceptual linear prediction
(PLP) preprocessing. It uses
bandpass filter
A band-pass filter or bandpass filter (BPF) is a device that passes frequencies within a certain range and rejects ( attenuates) frequencies outside that range.
It is the inverse of a '' band-stop filter''.
Description
In electronics and s ...
ing in the
log spectral domain. Rasta filtering then removes slow channel variations. It has also been applied to
cepstrum
In Fourier analysis, the cepstrum (; plural ''cepstra'', adjective ''cepstral'') is the result of computing the inverse Fourier transform (IFT) of the logarithm of the estimated signal spectrum. The method is a tool for investigating periodic st ...
feature-based preprocessing with both log spectral and cepstral domain filtering.
In general a RASTA filter is defined by
The numerator is a
regression filter with N being the order (must be odd) and the denominator is an integrator with time decay. The pole controls the lower limit of frequency and is normally around 0.9. RASTA-filtering can be changed to use mean subtraction, implementing a moving average filter. Filtering is normally performed in the cepstral domain. The mean becomes the long term cepstrum and is typically computed on the speech part for each separate utterance. A silence is necessary to detect each utterance.
References
*https://labrosa.ee.columbia.edu/~dpwe/papers/HermM94-rasta.pdf
Signal processing