ASTi Telestra Service Manual download pdf (Page 33)

ASTi ACE Studio Components Reference Guide Rev. M DOC-01-TELAS-CRG-4

2.9. Filter

Summary: The Filter component applies a filter to an input signal. The type of

filtering applied may be lowpass, bandpass, or highpass. The filter quality factor,

rolloff frequency, and gain can be controlled by input variable from elsewhere in

the model or from the host interface.

Description: The Filter component applies to an input signal. The type of filtering

applied may be lowpass, bandpass, or highpass. The filter quality factor, rolloff

frequency, and gain can be controlled by input variables from elsewhere in the

model or from the host interface.

The input signal audio should be passed to the filter only if the derived output gain

is greater than 0.0.

The filter is controlled by the parameters: Enable, Type, Filter Frequency, and Q

Factor. The Filter Enable control is specified by an externally controlled variable

and an XOR logic gate control. XOR logic is applied to the external variable and

the gate control to derive a final value for the Filter Enable flag. If no external

variable is connected, the value of the logic gate control becomes the Filter Enable

flag. If Filter Enable is set to False, no filtering is applied to the white noise.

Type determines the type of filter applied to the input signal (Off, Lowpass,

Highpass, or Bandpass). If Type is set to Off, no filtering should be applied to the

white noise. Filter Frequency (in Hertz) provides the rolloff frequency of the filter.

The meaning of the frequency depends on the filter type as follows:

Filter TypeFrequency Meaning

OffIgnored

LowpassUpper Bound Frequency

HighpassLower Bound Frequency

BandpassCenter frequency with bandwidth controlled by Q factor (see below)

Q Factor is the filter quality factor, which effectively determines the filter rolloff for

lowpass and high pass filters and the filter bandwidth for bandpass filters. Q factor

is inversely proportional to the filter rolloff or bandwidth.

The filter parameters are used to derive the filter coefficients for a 2-pole IIR filter.

If Q Factor is 0 or less, a very low non-zero value should be used for the k

calculation. The output from the filter is active only if the white noise source is

active. If the Filter Type is Off, the filter output signal is the input signal.

An amplitude gain control is applied to the filter output. This output gain control

consists of a connection to an external control variable and a scale factor. The value

of the external variable is multiplied by the scale factor to drive the output gain. If

no external variable is connected, the value for the scale factor becomes the output

gain.

The Filter component output audio should only be active if the following conditions

are true:

I. The output from the filter is active.

II. The derived output gain (external variable * scale factor) is greater than 0.0.

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ASTi Telestra Service Manual Page 33

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