Technical data

DOC-01-TELAS-CRG-4 ASTi ACE Studio Components Reference Guide Rev.M
62 Copyright © 2014 Advanced Simulation Technology inc.
2.26. Vox
Summary: The Vox component allows voice activated or push-to-talk (PTT)
control over an audio input signal. An optional filter may be applied to the input
signal. If the filtered input signal level exceeds the Vox threshold level, the Vox
component will output the signal. Once the input signal level has dropped below
the threshold, the Vox component will remain active for the period of time specified
by the Vox delay. Alternately, the Vox component can operate in PTT mode in
which the Vox component outputs a signal only when the PTT control is set.
Description: The Vox component operates on an input signal. The source of the
input signal is an external component that is connected to the Vox via an InSignal
variable.
The Vox component first applies a filter to the input signal. The output from the
filter is active only if the input signal source is active.
The filter is controlled by the parameters: Type, Filter Frequency, and Q Factor.
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
input signal. 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 highpass 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. If the Filter Type is Off, the filter output signal is the input signal.
If the output of the filter is active, the Vox component applies Vox or PTT control to
the filtered signal. The Vox component includes a Vox enable flag and PTT control.
The Vox and PTT controls are specified by an externally controlled variable and an
XOR logic gate control. XOR logic is applied to the external variable value and the
gate control to derive a final value for the Vox enable and PTT flags. If no external
variable is connected, the value of the logic gate control becomes the input value.
These two boolean inputs control when the Vox outputs audio as follows:
I. Vox Enable = False, PTT = False - No Output
II. Vox Enable = True, PTT = False - Output active only when signal level
exceeds the threshold
III. Vox Enable = False, PTT = True - Output active always (regardless of
signal level)
IV. Vox Enable = True, PTT = True - Output active always (regardless of signal
level)
For case II, if the signal level drops below threshold, the Vox component will
continue to output a signal for the duration specified in the Vox delay parameter.
The threshold level is specified by the Vox level control, which consists of a
connection to an external control variable and an offset. The value of the external
variable is added to the offset to derive the Vox threshold level. If no external
variable is connected, the value for the offset becomes the Vox threshold level.
An amplitude gain control is applied to the Vox output. This output gain control
consists of a connection to an external controlled variable and a scale factor. The
value of the external variable is multiplied by the scale factor to derive the output
gain. If no external variable is connected, the value for the scale factor becomes the
signal gain.
The Vox component output audio should only be active if both of 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.
The Summary View section contains two variables which are not an input, output,
or internal parameter. These are Filter Output Signal Level and Output Signal
Level. Filter output Signal Level reflects the RMS signal power at the output of the
Vox filter. This variable will be non-zero whenever the Input Signal is active.
Output Signal Level is the RMS signal power of the output from the Vox
component. This variable will only be non-zero if the component output is active. It
is possible for the Filter Output Signal Level to be non-zero while Output Signal
Level is zero. This would happen if the filtered signal does not exceed the Vox
threshold. If the output signal is active, both variables would have the same value.