Audiospektri Guitar Analyser Manual - Page 5

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Pedal effects The three position toggle switch selects one of three possible effects to be applied to

the synthetic signal, FM, vibrato or distortion.

FM is the classical FM modulation effect used in many synthesizers. The base signal

without any effects is pure sinewave without any harmonics. When the FM effect is

applied, several harmonics will appear, depending on the modulation strength. The

strength depends on two factors. The effect adjust or pedal will give a common

modulation strength coefficient to all the outputs. In addition, the amplitudes of the

individual strings will also control their individual modulation strength up to the

maximum set by the pedal or effect adjust potentiometer. A third important control is

the compressor gain potentiometer. When any of the string amplitudes reaches the

compressor limit, shown by the led next to its output, then obviously the string

amplitude remains constant and it has no further effect on the modulation strength.

Therefore, in order to keep the sound dynamic, adjust the compressor gain so that the

signal is not overly compressed. There is, however, no clipping when the output is

limited, it just remains spectrally constant.

The distortion effect is a simple effect that uses clipping and pulse duty cycle

adjustment to create more harmonics than the base sinewave. It is useful as an input

for additional waveshaping modules in the Eurorack. It has similar amplitude

dependent strength control characteristics as the FM modulation method.

The vibrato effect needs to have the pedal connected. When the effect adjust

potentiometer is at zero, the pedal will control the upwards pitch bend, up to a one

fourth interval. Otherwise the potentiometer controls the vibrato frequency and the

pedal the strength, i.e. the deviation of the vibrato frequency around the base pitch.

Limitations The string pitch analysis has some limitations, because all the six string signals come

stacked together in a standard guitar pickup signal. The main limitation is that the

software does not recognize such string notes that fall on the harmonics of a lower

base note. The practical limitations are mainly relevant only with the octave interval,

and the octave + fourth (=3rd harmonic) -interval, i.e. a note blocks all its higher

octave notes, as well as notes above the octave + fourth pitch. In order to not

unintentionally block higher harmonic notes, the player should dampen those lower

strings that are not played, and/or adjust the "threshold" knob more clockwise.

The frequency resolution vs. amplitude has limitations as well: the string detection

software resolution goes down to one seminote, but a strong neighboring note may

obscure a weaker note +- one seminote apart. Another limitation comes from the

delay of the analysis. A few cycles are needed to find the frequency of each note. The

frequency resolution and latency are tied together: higher resolution inevitably means

longer latency and vice versa. Therefore we have tried to achieve a good tradeoff

between an acceptable latency and good enough note discrimination resolution.