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IntroductionGoing Through an AS Session > Filtering the Sound > Setting Filters
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Setting Filters

Creating a Filter

Rectangular Surface Filter and Sonogram

The rectangular surface filter is the default tool to apply a filter in a time/frequency area of the spectrum. This filter allows to globally increase or decrease the amplitude of the spectral components. Once this surface is created, its features – dimensions, intensity, contour – can be modified.

  • To draw a surface filter on the sonogram, select the red/blue square tool and click and drag the mouse on the sonogram. A grey rectangle appears.

  • To modify the filter's duration or frequency area, hover the mouse over the desired edge of the filter until a double triangle appears. Then, click and drag the mouse.

  • To move the filter, click and drag it.

Setting and manipulating the filter from the sonogram and treatment sequencer.
Setting and manipulating the filter from the sonogram and treatment sequencer.
Processing Sequencer

As you noticed, the filter is also represented in the Processing Sequencer, below the sonogram. This sequencer allows to edit this filter independently from any manipulations in the sonogram.

More Information about the Processing Sequencer
Setting Intensity

By default, filters are on Gain mode. This means that the user can choose freely the amount of gain to be added or substracted to the spectral components, from 116 to -116 dB.

To set the intensity gain or loss

Ctrl click on the surface: a double arrow appears.

Scroll the mouse up or down.

The square will get blue or red, depending whether the intensity if increased of decreased. We will set filters to -116 dB, which actually amounts to "shut down", or reject the spectral components.

Reject/Pass Modes
  • The Reject mode allows to reduce the intensity of the selected region completely.

  • The Pass mode allows to reduce the intensity of the other regions completely.

More about Filters
Intensity Gain and Loss

The dB value of the filter is applied globally to the whole area of the spectrum. If the intensity of the area is increased beyond the limits of the system, be careful not to choose values which could lead to clipping[1] the signal.

Basic Edition Commands


Standard manipulations, such as cut copy-paste or delete, can be applied to filters in the sonogram window, or in the processing sequencer.

  • To copy a surface filter

    1. select it with a click in the sonogram or in the sequencer,

    2. press Cmd C + X or use the Edit/Copy-Cut menu

    3. set a location with the cursor

    4. press Cmd + V or use the Edit/Paste menu

  • To delete a filter, select it and press Backspace.

  • To move, copy or delete several filters, SHIFT click on the filters or their representation in the sequencer, and use the standard manipulations and shortcuts described above.


If you don't select another location, the new filter will be superimposed on the original filter, and won't be visible. Click and drag it with the mouse.

Global Modifications

The intensity of several filters can be modified globally. mouse drag and Backspace. Their intensity can also be globally increased or decreased via the sonogram, or the sequencer.

Select the filters with a SHIFT click in the sonogram window or in the processing sequencer.

To change their intensity,

  • Double click on one of the filters representation in the sequencer, enter a value and choose OK.

  • Ctrl click on one of the filters and scroll the mouse up of down. Note that the intensity of both filters will be reset according to the value of the filter that was clicked on.

Parameters Edition

Inspector Window

The filter's characteristics –area, intensity and contour – can be edited via the inspector window.

Select the filter with a click, double click in the desired prompt, type a value and press Enter.

Treatment Internal Editor

The gain of the filter can also be modified via the treatment's internal editor from the processing sequencer:

  1. double click on the filter's representation

  2. enter a value

  3. press OK.

More Information about Filtering Parameters


The resulting sound can be pre-listened to before processing the treatments. Click on the corresponding command of the player:

This command can be used as a play/stop command. You can also stop the play with the space bar.

  1. Audio Clipping

    Clipping is a form of waveform distortion that occurs when an amplifier is overdriven. The signal is amplified at which point the signal simply "cuts" or "clips" at the maximum capacity of the amplifier. The extra signal is simply cut off, resulting in a sine wave becoming a distorted square-wave-type waveform

    In digital signal processing, the signal is restricted by the range of a chosen representation. For example, in a 16-bit system, 32767 is the largest positive value that can be represented. If the amplitude of the signal is doubled, sample values of, for instance, 32000 should become 64000, but instead they are truncated to the maximum, 32767.

    Source :

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