Description:

When long wavelengths reflect in the room, the direct sound interacts with the reflections producing regions of excess phase which result in cancellation. The ICPA function compensates for the excess phase by creating an all pass filter that can be inserted into the same channel or opposite channel depending on the Q of the filter. The Group Delay display is shown. Areas of minimum phase are in the flat region of the graph, and areas of 3 excess phase are shown as peaks. The 1 Upper Q Limit and 2 Lower Q Limit are also shown. Corrections of peaks above or below the Q limit should not be performed.

Use:

Perform the operations in the following order.

1. Find an excess phase peak in the Group Delay graph and left click on it to place a marker. Take note of the colour (red = left, green = right)

2. Select the source channel

3. Click on “Get marked frequency” to load the frequency into the dialog box

4. If necessary, you can zoom in to the peak of interest via left/right click on the graph and using the zoom controls. You can then place the marker with more accuracy.

5. Adjust the f0 and Q of the all-pass filter

6. Click on “Demo Edited Values” to preview the shape of the filter. It should match the excess phase peak as closely as possible. Several iterations of 5 and 6 are necessary to obtain a close match.

7. When satisfied with the appearance of the filter, click “Simulate and Optimize”.

8. Finally click “Save Result”. The filter will appear in either the left or the right channel.

Opt1: Deletes the selected filter

Opt2, Opt3: Acourate automatically places the filter in the left or right channel depending on the Q. You can over-ride Acourate by manually placing the filter if you wish.

Finally run Macro 4 to generate the filters. Ensure the “ICPA” option in Macro 4 is ticked. Please note that verification of the ICPA function requires a mono recording (left and right channels playing together)