6
Vocodizer
Voiced/Unvoiced Detection
The Voiced/Unvoiced Detection feature
examines the analysis input signal for its
tonal and noise content to determine
which is dominant.
Type: The Detection algorithm can
operate in one of two modes depending
on some specific signal criteria.
Standard Mode (Type = off)
In standard mode the Vocodizer splits the
signal’s energy content into high and low
frequency components by means of two
filters, and then analyzes the two
components separately. By adjusting the
Threshold setting you can determine how
conditions: Only if the high frequencies
contain sufficient energy AND the low
frequencies do not, will the Vocodizer
interpret the signal as being unvoiced.
Example: A pure "s" sound contains
sufficient high frequencies to satisfy the
requirements of the first criterion, but the
lower frequency energy is not sufficient
to qualify it as a tonal sound (second
criterion). The Vocodizer interprets this
signal to be unvoiced.
With the same settings, the detection
circuit now encounters a spoken "k"
sound. As before, the high frequency
component is determined to be
sufficiently high in energy to qualify it as
an unvoiced signal. But this time there is
also enough tonal energy in the low
frequencies to override the initial
determination, and the Vocodizer
interprets the signal to be voiced. You can
adjust the relationship of the weighting
of the two criteria with the Hyst (Hyste-
resis) setting.
Lowpass
Highpass
much high frequency content triggers the
detection circuit to identify the signal as
unvoiced. However, at the same time, the
Vocodizer also examines the spectrum of
the low frequency component. The
Vocodizer therefore considers two
Voiced/Unvoiced Detection, as we have
said, determines whether the input signal
contains noise (like a sibilant "s" sound)
or tone (like a spoken "a", or other vowel).
Depending on the content, one of two
possible signals is sent to the synthesis
filter bank: Unvoiced source (usually
noise) or Voiced source (the filtered
internal synth or external audio source).
