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When the TAPS+FB button is pressed a second time the COMB FEEDBACK edit page is displayed. This allows
the configuration of the feedback filtering and feedback path nonlinearity. There are four possible settings:
◊
Guitar
In this configuration there is no nonlinearity, and the feedback filter is set to a simple exponential
averaging. This gives a structure similar to that used in the classic Karplus-Strong string synthesis, hence
the name “Guitar”.
◊
sitar
In this configuration the feedback filtering is the same as for guitar, but there is an added
nonlinearity in that the comb size is modulated slightly by a rectified version of the comb input signal.
This models the effect of the curved bridge of a sitar, where the length of the string changes slightly
depending on the string’s displacement. The effect of the nonlinearity is only noticeable at higher
feedback levels and is most pronounced when doing pitch bends (i.e. when the comb size is changing).
◊
Clarinet
In this configuration the feedback filtering is the same as for guitar, but there is a nonlinearity
in the feedback path. This causes the generation of odd harmonics, giving the sound a “hollow” character
similar to that of a square wave.
◊
Raw
In this configuration the output of tap #64 is fed directly back into the input, with no filtering or
nonlinearity applied.
Don’t be afraid to turn up the comb feedback beyond the point where self-oscillation occurs! By using
the 1V/OCT input to controll the comb size, you can “play” the comb resonator as a sound source, since
the frequency of the self-oscillation will be determined by the comb size. The sound of the self-oscillation
will be different in the different COMB FEEDBACK modes. The cleanest sound is obtained when in Clarinet
mode, while the Sitar mode will give a more haotic noise unless the feedback level is very close to the
self-oscillation threshold. The Raw mode will give the typical distorted amp feedback sounds, while the
Guitar mode will give an interesting noisy phased sort of sound.
●
CLK sRC
Displays the clock source (highlighted), the current comb time in milliseconds, and the clock
division factor. Turning the rotary encoder will change the source of the signal defining the comb size.
The choices are COMB CLK, COMB SIZE, and Encoder. When
COMB CLK
is selected, and a clock signal
is connected to the (right-hand) CLK input jack, the comb size will follow the period of the clock signal,
multiplied by the CLK DIV value. In this situation the COMB SIZE potentiometer, the SIZE input, and the 1V/
OCT inputs will have no effect.
When
COMB SIZE
is selected, the comb size will be set by the sum of the 1V/OCT input, the SIZE input and
the COMB SIZE potentiometer setting. In this mode the comb size is affected by the CLK DIV setting, where
doubling the CLK DIV value will double the comb size. This is useful in setting the overall range for the comb
size controls.
When
Encoder
is selected, then the comb size can only be changed by turning the rotary encoder, while in
the SIZE display mode (see below). In this situation the comb CLK , SIZE, and 1V/OCT inputs, the COMB SIZE
potentiometer, and the CLK DIV setting will not have any effect.
Note that the COMB SIZE control voltage signal has some low level noise, which can cause small random
jumps in the comb size, resulting in audible glitches in some situations, particularly when using large comb
sizes. In these cases you should set the COMB SIZE to Encoder unless you really need to have the voltage
control over the comb size.
When
DLY CLK/T
is selected the comb size will follow the rhythm delay time. This is useful for synchronizing
the comb and rhythm delay effects.
●
CLK Div
Displays the clock source, the current comb size in milliseconds,and the comb clock division factor
(highlighted). Turning the rotary encoder will change the CLK DIV (clock division factor) value. Possible DIV
settings are /1, /2, /3, /4, /6, /8, /12, /16, /24, /32, /48, /64, /96, /128, /192, /256.
●
siZe
Displays the clock source, the current comb size (highlighted),and the clock division factor. The comb
size is the delay time of the 64th tap in the comb. This tap has the longest delay time, so the comb size
gives the overall delay of the comb. The comb size is determined in one of three different ways, which are
selected by the CLK SRC setting (see above). The first way is to use the rotary encoder to directly specify the
comb size in millseconds. This is enabled when CLK SRC is set to “Encoder”. This is useful when you want to
dial in a precise, fixed, comb size value. When CLK SRC is set to “COMB CLK” the comb size is determined
by the period of the clock signal present at the (right-hand) CLK input, multiplied by the current CLK DIV
setting. This mode is useful for syncing to an external LFO or MIDI clock signal, for example. When CLK SRC
is set to “COMB SIZE”, then the comb size value is determined by the sum of the 1V/OCT, SIZE, and COMB
SIZE potentiometer voltages and by the CLK DIV setting. When the module is properly calibrated (done at
the factory), the comb size will be cut in half for every 1 volt increase in the 1V/OCTinput signal. This mode
is used when you want tuned resonances, for example when using the comb for Karplus-Strong string
synthesis. The SIZE input and the COMB SIZE potentiometer provide linear offsets to the 1V/OCT signal (much
like the Transpose control on a VCO).
●
fX ON
Switches the comb effect on or off. When the effect is on the red LED to the right of the button will
be constantly lit up. When the effect is off, the LED will also be turned off. When the effect is turned off the
comb section input signal is passed to the comb output. That is, the FX ON button acts as a
bypass
switch.
●
MUTe
Mutes/un-mutes the comb section. When the comb effect is muted, the red LED in between the FX
ON and MUTE buttons will flash on and off. The muting effect is on the input to the comb, and when muted
the comb input will be set to zero. The output will continue to regenerate if the comb feedback is turned up.
●
Comb siZe
When CLK SRC is set to COMB SIZE, this potentiometer is added to the 1V/OCT and SIZE control
voltage inputs and together determine the size of the comb (i.e. the delay time of the 64th tap).
●
COMB feeDBACK
This potentiometer adjusts the amount of signal fed back from the last (64th) tap in the
comb to be mixed with the input. The potentiometer voltage is added to the FEEDBACK control voltage.