UM1545 datasheet(24/64 Pages) STMICROELECTRONICS

24 / 64 page

APW walkthrough

UM1545

24/64

Doc ID 023225 Rev 1

Please note that when moving the mouse pointer to design a graph, the corresponding filter

coefficients are continuously computed and applied to the device according to the

preferences applied that will be discussed below. Also, the qualitative parameters of the filter

(Figure 21, highlighted in blue) are coherently updated.

Figure 21.

Equalizer Editor tab, the upper part (graphing and design tools)

To design a filter by defining its qualitative parameters, follow the procedure below:

Select the kind of filter to be designed by pressing the appropriate button on the right

side of the graph. It is also possible to select which biquadratic filter of the DUT to write

in (Figure 21, highlighted in red).

Enter the desired parameters in their corresponding fields on the right side of the graph

(Figure 21, highlighted in blue), then hit the “Enter” key to change the focus from the

input field to another control of the panel.

The graph is immediately plotted, the filter coefficients are computed and they are

applied to the device according to the apply option that will be discussed later on in this

section.

It is important to point out that one filter design method does not exclude another. Indeed, it

is possible either to modify the qualitative parameters of a filter designed starting from a

desired graph or to adjust the filter graph generated from a set of qualitative parameters.

Whichever is the design method applied, the hexadecimal values of the computed

coefficients are displayed in the area highlighted in green in Figure 21. When changing the

selected biquadratic filter, the table of coefficients is updated coherently.

Regardless of the filter design approach, the APW also embeds a set of controls to protect

the user’s hearing and the audio equipment from unpleasant effects when designing a filter:

●

Single filter gain limitation: the gain applicable with a single filter can be set between a

range varying from +15 dB to -30 dB. This range is fixed and cannot be changed. The

limits of this range are marked on the graph with a red line as shown in Figure 21. If a

higher gain is desired, this limitation can be bypassed using a chain of two or more

filters.

●

Auto-scaler: APW offers also the possibility of limiting the overall maximum positive

gain applicable with any chain of filters. This is done by enabling the Enable auto-scaler

checkbox. This feature automatically computes the difference between the overall filter

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