Frap Tools CGM - Manual Sampling; External Gate Sampling; Clock Outputs (Main and Random); Random Voltages

Rev. 5 – Jun 2020 Page 16 of 91
MANUAL SAMPLING
No matter if you are using the built-in clock or an ex-
ternal one, that stream can be temporarily bypassed with
the manual S&H Button (A.9).
By pushing the S&H button the stream of impulses is
overridden by a gate high signal, which samples a value
and holds it until it is released. A dedicated LED will light
up as long as the button is pushed. The main clock out-
put, however, will still output a trig signal.
Practice some uses of the buttons with this
Technique:
Hold
EXTERNAL GATE SAMPLING
This last operation can be automated using the Gate/CV
Input (A.7).
When the switch (A.8) is set to the rightmost position,
any CV signal higher than 3V can be patched in the
Gate/CV Input and used to override the internal clock.
With this configuration it is possible to use other signal
than gates and trigs to drive the S&H cluster, such as sine
or triangle waves or even the internal fluctuating random,
however a gate or a square signal generally provide best
results.
CLOCK OUTPUTS (MAIN AND RANDOM)
Every time the S&H Cluster samples a value, a 2ms trig
is outputted from the Main Clock output (14A.4). If a steady
pulse is used, such as the internal clock or an external one,
this output will provide an exact copy of the clock.
On the left of the Main Clock output lies the Random Clock
output (A.5), which can either add or subtract trigs from
the one in use through its switch (A.6), located between
the two clock outputs.
When the switch is up, or in additive mode, it outputs
all the clock impulses generated from the clock with the
addition of other random clocks; when the switch is
down, or in subtractive mode, it randomly subtracts trigs
from the ones generated to trig the S&H Cluster, i.e. it
outputs only some of the trigs that are outputted by the
Main Clock out.
In both modes, the random clock density depends on
the Global Rate of Change (See below, §4.3).
Practice the clocks with these Techniques:
Random Clocks #1
Random Clocks #2
Ratcheting-Like Effect #3
Clock Bursts #1
Clock Bursts #2
Since SAPÈL’s clock is 2 milliseconds long, it
works really well if patched to FUMANA’s Mod-
ulation Input:
Percussion Sounds #2
4 RANDOM VOLTAGES
SAPÈL is designed to provide a vast array of random
voltages with different articulations at the same time.
Each of the two S&H clusters (yellow and green) can be
divided into two units: the first one generates three ran-
dom voltages simultaneously, and it is activated by the
clocks or gates described above; the second one generates
continuous, fluctuating random values and it is com-
pletely independent from the clocks and gates.
NON-QUANTIZED RANDOM VOLTAGES
The most basic stepped random values generator is the
Sample and Hold circuit, which outputs its values
through the S&H output (B.1)
This generator is designed with an independent ran-
dom generator and creates non-quantized stepped volt-
ages with a range varying from 0 to 7.5V. Non-quantized
means that if the values are used, for example, to modify
the pitch of an oscillator, the result will be a series of
sounds whose frequency may not sit within the conven-
tional 12-semitone Western chromatic scale. It can be
used for more experimental music compositions or, more
traditionally, to modulate other non-melodic parameters
such as timbre, filter frequency, amplitude…
QUANTIZED RANDOM VOLTAGES
The other two stepped random voltage generators out-
put voltages which are quantized (i.e., “forced”) to the
1V/octave standard. If applied to an oscillator’s fre-
quency, the result will be a series of random “notes”
The design of these two generators follows the historical
Buchla module Source of Uncertainty Model 266, but
with a substantial different approach. The circuit has
been designed from scratch in order to obtain a more
“random” voltages distribution and an extremely precise
voltages quantization, capable of generating precise sem-
itones or octaves.
At first glance, the main difference with the S&H circuit
mentioned above is that the quantized random voltage
generator features a knob which controls the n parameter
and whose range goes from 1 to 6, as in the original 266
module. The role of the n parameter varies according to
each generator’s label: 2
n
and n+1.
The 2
n
Output (B.5) is quantized in 1/12V steps, or sem-
itones in the 1V/oct scale. In this case, the Value knob sets
the exponent of 2 which, in turn, determines the number
of different values that may be generated by the circuit.