Audiospektri PGV Podręcznik - Strona 3

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The "threshold" knob controls the input level of the guitar signal analysis section. The user has to

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adjust it to an optimal position for their particular guitar: if set too low, there is a risk of getting spurious

low-level signals for the note pitch analysis logic, and if too high, there is a risk of missing some notes,

especially from the higher pitched strings. The control is not very critical, the center position is a good

start. Always use the guitar neck pickup for the most reliable detection.

Because the output signal of the PGV has to be a sensible combination of both the vocal microphone and the

six guitar string signals that all have a wide dynamic range, signal compression is a critical part of the PGV

software. The vocal microphone signal does not have any input gain adjustment. It is set for a typical dynamic

microphone, and there is a fixed compression threshold above which there is no amplitude increase for louder

vocal amplitude. The green LED "mic compressor" shows when this level is reached. The green light does

not mean that the signal is clipped or distorted, and for normal operation, the user is recommended to sing loud

enough so that the green LED is on. That makes for optimal vocoder dynamics.

The "mic gain" knob is used to control the mic compressor output gain to the second section of the

compressor that also handles the six guitar string signals. That part also has a green LED marked "guitar

compressor". It shows when the total signal reaches the final output compression level. The total signal can be

a maximum of six replicated vocal signals at the guitar string note frequencies. The player-singer needs to

adjust the "mic gain" so that the output dynamic range is satisfactory. Again, green light does not mean that

the signal is distorted, but if it is on all the time, the compression reduces the instrument's dynamic range

because the volume may stay constant from when one or all strings are played. The compressors generally

make sure that no output signal clipping occurs; however there are multiple complex signals, so just in case any

of the LEDs turn red, the player should lower the "mic gain" knob. Also check that the pilot signal is not active

at the same time as the vocal mic.

If the pilot signal is being used instead of the vocal signal, the compressors have additional significance. Three

controls are now essential: the "noise gate / pilot gain" controls the pilot amplitude (from the center location to

fully clockwise). The modulation strength of the pilot signal is controlled by the "VCF" knob, or the expression

pedal if the 3-way position switch is in the VCF position. When the knob/expression pedal is in the minimum

position, the pilot signal is pure sinewave, but if the "VCF" knob or expression pedal is activated, the pilot

signal's modulation depends on the guitar strings' amplitude, i.e. it has higher harmonics with higher amplitude,

and the knob or pedal controls sensitivity for the modulation. The "mic gain" knob controls the dynamics of the

modulation. When the "guitar compressor" LED turns green, i.e. the compressor limits the amplitude, the

modulation stays static, unlike below compression level. Therefore the "mic gain" knob should be adjusted

lower for a maximum dynamic effect that follows the guitar picking strength.

The behavior of each special effect selectable with the 3-way position switch is explained shortly:

"spectrum shift": If the 3-way switch is in the lowest position, the connected expression pedal controls

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the vocal spectrum shape. Otherwise the knob "spectrum shift" is used for the same control. This

control compresses or expands the vocal spectrum (timbre) within the limits of the scale factors 0.7 –

1.5. The effect sounds like converting the speech to a "giant speaker" – "baby speaker" voice.

"VCF": This effect is a pseudo-voltage controlled filter that manipulates the vocal spectrum by

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attenuating bands selectable by the expression pedal when the 3-way switch is at the center position,

or otherwise using the corresponding knob. Remember to return the potentiometer to full counter

clockwise if you do not want to retain the filtering effect in the other positions of the switch. For the pilot

signal, it is instead the modulation sensitivity control, as explained in the previous section.

The use of the I/O signal and compressor controls

The special effects