INSPIRIA SA3286

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11

Biquad Filters

Additional frequency shaping can be achieved by

configuring generic biquad filters. The transfer function for

each of the biquad filters is as follows:

H(z) + b0 ) b1

1 ) a1

Note that the a0 coefficient is hard−wired to always be ‘1’.

The coefficients are each 16 bits in length and include one

sign bit, one bit to the left of the decimal point, and 14 bits

to the right of the decimal point. Thus, before quantization,

the floating−point coefficients must be in the range −2.0

≤ x

< 2.0 and quantized with the function:

round x

After designing a filter, the quantized coefficients can be

entered into the PreBiquads or PostBiquads tab in the

Interactive Data Sheet. The coefficients b0, b1, b2, a1, and

a2 are as defined in the transfer function above. The

parameters meta0 and meta1 do not have any effect on the

signal processing, but can be used to store additional

information related to the associated biquad.

The underlying code in the product components

automatically checks all of the filters in the system for

stability (i.e., the poles have to be within the unit circle)

before updating the graphs on the screen or programming

the coefficients into the hybrid. If the Interactive Data Sheet

receives an exception from the underlying stability checking

code, it automatically disables the biquad being modified

and display a warning message. When the filter is made

stable again, it can be re−enabled.

Also note that in some configurations, some of these

filters may be used by the product component for

microphone/telecoil compensation, low−frequency EQ, etc.

If this is the case, the coefficients entered by the user into

IDS are ignored and the filter designed by the software is

programmed instead. For more information on filter design

refer to the Biquad Filters In PARAGON Digital Hybrid

information note.

Rocker Switch

The Inspiria SA3286 is equipped with a rocker switch

feature that can perform both volume control (VC)

adjustments or an audio memory switch.

There are 3 modes of operation:

In Mixed Mode, the switches behaviour is configurable to

be set to that a short or long press of the switch will invoke

either a memory or VC change (i.e., a short press is a

memory select, a long press is a VC change).

There is a programmable threshold that can be used to set

the timing behaviour.

Volume Control

The Volume Control (VC) can be either external or

programmable. If external VC operation is selected, a

further decision is required as to whether a variable resistor

(analog VC) or a Digital Volume Control (DVC) will be

connected to the 9−bit A/D converter.

Analog Volume Control

The external VC can be configured to work with either a

two−terminal 200 k

W variable resistor or a three−terminal

0.1 M

W − 1MW variable resistor. In two−terminal

configuration, the VC is connected between GND and the

VC input. In three−terminal configuration, it is connected

between GND, Vreg and the VC input.

If using a two−terminal VC, it must be calibrated before

use. Calibration is not necessary with a three−terminal

connection. Hysteresis is built into the VC circuitry to

prevent unintentional volume level toggling. A log taper

potentiometer is recommended so that gain in dB would be

linear with potentiometer rotation. The range of VC is

adjustable and can be set between 1 dB (min) and 42 dB

(max).

Digital Volume Control

If using a Digital Volume Control with the Inspiria

SA3286, a resistor must be connected between the VC input

and Vreg, and another resistor of the same value must be

connected between the VC input and GND. The values of

both resistors can be between 50 k

W and 0.5 MW.

A toggle switch can be used as a DVC, momentarily

connecting the VC to either Vreg or GND. By connecting the

VC to Vreg, the volume will be increased one step, and by

connecting the VC to GND, the volume will be decreased

one step.

The following parameters can be programmed into the

hybrid to specify the DVC functionality:

If the Max/Min beep is enabled then when the volume has

been incremented to the maximum value of the specified

DVC range the device will play two beeps to indicate that it

cannot increase the volume any more. The same is true for

decrementing the volume and reaching the minimum value

of the DVC range.