Robustness Techniques for Feature Extraction - Berlin Chen

Spectral Subtraction (SS) S. F. Boll, 1979
• A Speech Enhancement Technique
• Estimate the magnitude (or the power) of clean speech by
explicitly subtracting the noise magnitude (or the power)
spectrum from the noisy magnitude (or power) spectrum
• Basic Assumption of Spectral Subtraction
– The clean speech s [ m]
is corrupted by additive noise n[ m]
– Different frequencies are uncorrelated from each other
– s [ m]
and n[ m]
are statistically independent, so that the power
spectrum of the noisy speech x[ m]
can be expressed as:
P ( ω ) = P ( ω ) + P ( ω )
X
S
N
– To eliminate the additive noise: P ( ω ) = P ( ω ) − P ( ω )
S
X
N
– We can obtain an estimate of P N
( ω ) using the average period of M
frames that known to be just noise:
Pˆ
1
M
M
( ) ∑ − 1
ω = ( ω )
P N N ,i i=
0
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