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input signal reaching a value of 15 is greater than X, then only note E2 would be
played. If the time taken was less than X and more than 1/2X, then notes D2 and E2
would be played. Less than 1/2X then C2, D2 and E2, and so forth. In practice, the
timing rules were used like this alongside the threshold values and also separately
on their own. They were mapped to parameters ranging from audio effects settings
including delay,
filter and distortion parameters and audio playback sample chop-
ping controls such as playback position, pan position, and texture blending.
Further complexity was added through exploiting the features of using timers. A
hold-and-release function allowed for a change in control to occur at the point of
release. The time between the hold command and the release command being
received provided selectable options. When an input value increases, a timer begins
until the value decreases. Upon this decrease, the value of time is compared against
a series of rules. In practice, the accuracy of brainwave control can vary due to a
range of factors such as tiredness, environment, mood and electrical interference. To
accommodate this instability when attempting to sustain brainwave amplitude
through SSVEP, a further time delay rule monitors the EEG. For example, if we
de
ne a threshold input value of 5, so that when the input value increases above 5 a
hold command is activated. If the input stays above 5, then the hold command stays
on, and if the value decreases below 5, it is released. To add some
flexibility to this
simple hold-and-release function, a time delay of 3 s is added to the hold function.
Therefore, if the input decreases below 5 for less than 3 s and then increases to
above 5, the hold command remains on. If the input decreases to below 5 for longer
than 3 s, then the release function is activated. This technique creates a rule
whereby an icon needs to be
fixated on constantly to generate a command sent to
the performance system, akin to the constant attention required to play a sustained
note on an acoustic instrument. Deviation from this attention is allowed for a time
span of up to 3 s, allowing for the performer to utilise other input commands to
manipulate the sound via different parameters or to control other aspects of the
music. This
flexibility can able help combat irregularities in the input signal. To
help performer calculate times during a performance, a digital clock display was
built into the visual interface.
10.9.3 Ordering
The mappings and structure of the The Warren were designed to allow loose
periods for the performer to
'
'
the system. Within this it was unlikely that the
exact manner in which the controls were used would ever be the same twice. To add
a layer of surprise and quasi-randomness to the piece, as well as to further engage
the concentration of the performer to adapt to the system secondary mappings were
dominated by applying rules to the order in which icons were selected and which
commands were triggered. At times, these rules were mapped to stochastic musical
parameters ensuring a controlled level of unpredictability.
play
 
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