Audiospektri HG-16 black Instructions For Use Manual Download Page 13

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Mode 2: Comb filtered pseudoperiodic signal

Mode 2 uses a white noise source as an input to a comb filter, thereby creating a pseudoperiodic harmonic signal.
The speed of the filter is adjusted using the input note control voltage, therefore the apparent pitch of the
pseudoperiodic signal follows the same calibrated note pitch as the other modes.

The comb filtered signal is fed to a 15 channel bandpass filter and its output levels can be adjusted with the first 15
sliders, and modulated by any of the 4

envelope input

sources, selectable as described before. Furthermore, the

comb filter feedback can be adjusted making the output signal more or less noisy: i.e. when there is no feedback, the
white noise is fed raw to the 15 BP filters. The filters are also tuned to harmonic center frequencies, so the same
apparent pitch still remains, although very noisy. When the comb filter feedback approaches unity, the noisiness
decreases and the signal goes closer to a periodic harmonic signal; if only one slider is up and others in the fully
attenuated position, the signal is closest to a sinusoid, but obviously still quite noisy.

The comb filter feedback coefficient can also be adjusted and modulated, allowing very dynamic sounds to be
made, varying between noisy and more sinusoidal signal with the envelope amplitude. The modulating envelope has
to be connected to the

modulation 1

input. The sensitivity for the modulation can be adjusted using the

adjust 2

knob, and the modulation feedback offset value corresponding to zero modulation amplitude using the

adjust 1

knob. The modulation direction can be either from noisy to less noisy, or the opposite direction. This is controlled
by

Slider 16

that works in on/off mode: when

Slider 16

is fully down or off, increasing modulation amplitude

increases the noise level, and when

Slider 16

is up, increasing modulation amplitude decreases the noise level.

Note that the release rate from high noise to low noise is slow, because the comb filter stabilization takes some time.
When moving to the opposite direction the rate is fast.

modulation 2

has no effect in this mode. Furthermore, the Eurorack gate signal is not used in this mode, even if the

toggle switch is in the “

” -position. Therefore the output level is all the time controlled by the external

envelope

inputs

linked to the corresponding sliders.

Notice that because the signal is fully created from noise, the noise floor is also much higher than in the other
modes. This is not a flaw but inherent for this synthesis method, because this mode uses subtractive synthesis, and
the applied bandpass filters do not have infinite stopband attenuation. You can also note that the noise floor is
clearly lower if you move slider 1 off and instead use the other sliders for the corresponding amplitude control of
the pseudoharmonics.
This mode has been found especially useful for noisy flute -type of voices. This is demonstrated by several sound
samples in the download section, including exaggerated samples. You can also hear a clear difference from the
signal of e.g. Mode 0 even if you try to adjust the harmonics noise bands equal. All noise is not created equal!

As a summary, here is a list of the patch cable connections required:

Connect envelope generator outputs to all those of the

envelope inputs

that you have activated for the

desired harmonic sliders. Only sliders 1 to 15 are usable in this mode. Remember that on power up,
all are connected to

envelope input 1

, and only if you toggle the switch to "envelope select" position

and back again, the previously stored connections are activated.

If you want to have the noise modulation function, connect also envelope generator output to

modulation 1

. If you want to keep the noise at constant level, you can alternatively connect

modulation 1