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IntroductionSignal Manipulation > Dynamic Filtering > MultiBand Filters > Constant Filtering
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Constant Filtering

The multiband filter can be used as a single or multiple pass or reject band, whose values can be edited afterwards. It resembles a standard BPF, but shows a number of restrictions regarding manual and parametric values edition.

Creating Filters

Access

With an open sound file, choose Treatments/MultiBand Filter.

A dialogue window will open.

Dialogue Window

The dialogue window is divided in four zones, and allows to set global filtering parameters :

  • Filter type and number of bands

  • Band width, position and characteristic frequency.

  • Spacing interval between bands

Specfiy the desired values and press OK.

Filtering Level and Slope

The filtering level is always set to a negative maximum, -116 dB. The filter's slope cannot be defined.

Display

The filter bands will appear in the Sonogram window, with the usual corresponding block in the Processing Sequencer.

  • Reject bands are displayed in red

  • Pass bands are displayed in grey

A point is displayed at each extremety of the filter : the filter is selected by default. If the filter is not selected, the points will be hidden.

The Inspector will display the main parameters of the filter :

  • Start, end and duration of the treatment

  • Filter type : pass or reject

  • Number of bands.

Subsequent Modifications

The filter parameters can then be modified via the Sonogram window, the Processing Sequencer and the Inspector.

The BPF in the sonogram window can be used to modify the filters dynamically.

Basic and Advanced Treatments Manipulation and Edition

Parameters of the Dialogue Window

Filter Type and Amount

  • Band Pass / Band Reject : this parameter can be modified afterwards.

    • Band pass : frequencies beyond the limits of the filter won't be heard.
    • Band reject : frequencies within the limits of the filter won't be heard

  • Number of bands : enter number in the prompt. Note that defining a band implies one or two bands of the other type below and/or above it.

Band Width, Position and Characteristic Frequency

These parameters offer several interesting options that allow to use filters according to standard criteria based on a position and width expressed with frequencies, or to think of them more as "tuned" components if you tend to think in terms of musical pitch. Of course, thinking in termes of frequency relationships is compatible with a musical prospect too.

These parameters characterize the lowest band, which is used as a reference for other parameters.

  • Center/Start Frequency : a characteristic frequency for the filter. Select a menu item in the popup menu and enter a value in the corresponding prompt. If you select a start frequency, the value will be that of the lower limit of the band.

  • Pitch pop up menu : to define this value according to a pitch, select an item in the rightmost popup menu. The corresponding frequency – with a 440 A4 tuning – will be calculated automatically.

    This pitch is also converted automatically when entering a frequency in the adjacent prompt.

  • Filter Bandwidth : choose a value in Hz or in cents – 100 cents = a semitone. Note that if a band exceeds the lower limits of the sonogram, two points will be displayed at the bottom of the band anyway, so that it can be edited.

Bands Manual Edition
Interval Between Successive Bands

This interval can be set with a value in Hz or in cents, or match the values of the harmonics of the reference lower band.

  • Band Interval : Choose an intem in the pop up menu and enter a value in the prompt. Bands will be spaced regularly according to this interval, which can be in a harmonic relationship with the reference band or not.

  • Follow Harmonics : the upper bands characteristic frequency is in a harmonic relationship, that is, the produce of the reference frequency with an integer.

Note : Fine Tuning

Filters can be "tuned" with specific intervals and bandwidth with a manual edition once they are added in the sonogram window, and/or adding new multiband filters.

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