Image Processing Reference
In-Depth Information
These frequencies are removed
Response
Figure 37-2
High-pass filter
response.
Frequency
frequencies. Add notch filters at harmonics of these frequencies (although the harmonic
content will reduce in the higher overtones).
37.4.2
A Rumble in the Jungle
Rumble from turntables is removed with a high-pass filter (Figure 37-2). Be aware that
there are useful bass frequencies in music as low as 30 Hz, and you may want to preserve
these.
37.4.3
Hissing Fits
Similarly, there are high-frequency components that you want to preserve while removing
hiss. Hiss is removed with a low-pass filter (Figure 37-3), but this should be gated so that
you don't lose program material. Then the filter can clean the quiet passages and be deac-
tivated when the noise won't be noticed.
These frequencies are removed
Response
Figure 37-3
Low-pass filter
response.
Frequency
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