sigFile::dcblock

sigFile::dcblock
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dcblock is a filter which removes very low frequencies from a soundfile. A good use for the dc-blocking filter is to remove a DC offset (0 Hertz frequency) from a sound recorded with a microphone which might have added a constant voltage offset. For example, here is a picture of a soundfile on the left which has a noticeable dc offset. The picture of the same sound on the right has been passed through the DC-blocking filter, and is now centered around rather than above the zero line.

The degree to which low frequencies are blocked is determined by the parameter specified by the -p option. A typical value for -p is around 0.995 which is the default for the program. Lower values given with the -p options attenuate more frequencies. Here is a graph showing attenuation for various pole locations, a, which can be given to the -p option:

Pole values can be given either as a single number or as a time-varying envelope. As a complex function, the DC-blocking filter consists of a single zero located at z=1, and a pole located on the real axis somewhat close to the zero (usually around z=0.995):

Here is the flowgraph of a DC-blocking filter:

If no input soundfile is specified as an argument to the dcblock program, then whitenoise will be generated as an input signal.

usage

Usage: dcblock [-p pole][[-a amp][-d duration|-s samples]|insound]
outsound

Options: 
   -p = pole position envelope (default is "0 0.995 1 0.995")
   -d = duration in seconds of whitenoise if used (default 1.0)
   -s = duration in samples of whitenoise if used (default null)
        overrides -d option if specified.
   -a = amplitude envelope of whitenoise if used (default is "0 1 1 1")

examples

# dcblock examples:
#   Here is an example for dcblock which makes a soundfile with
#   dcblocked whitenoise
       dcblock -d 1.0 blocked.snd

craig@ccrma.stanford.edu