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D. Rocchesso: Sound Processing
analog-to-digital converter
digital-to-analog converter
memory buffers
harmonizer
as a prototypical example of such systems, and to see how our problem of sound
echoing and continuous transposition would have been solved with such system.
In the IRIS ARES/MARS workstation there is a host computer, that is used
to program the audio patches and the control environments, a micro-controller
that uses its proprietary real-time operating system to handle the control signals,
and one or more digital signal processors that are used to process the signals
at audio rate. The audio patch that solves our processing problem is shown in
fig. 5. The input signal is directly taken from an analog-to-digital converter, and
the output signal is sent to a digital-to-analog converter.
Figure 5: MARS patch for echoing and linearly-increasing transposition
There are two main blocks: the first, called HARMO, is responsible for input
signal transposition. The second, having a small clock as an icon, produces the
echo. Since we want a gradually-increasing transposition, the HARMO block is
controlled by a slowly-varying envelope, updated at a lower rate, programmed
to ramp from trasp iniziale to trasp finale. The transposed signal goes
into the delay unit and produces the echo that gets summed to the transposed
signal itself before being sent to the output. Among the parameters of the HARMO
and delay units, there are those responsible for memory management, since
both units use memory buffers that must be properly allocated, as explained in
section B.5.
Figure 6 shows a possible solution to our sweep-and-echo problem using pd.
Again, we have a harmo block that performs the pitch transposition. However,
in pd this harmonizer is not a native module, but it is implemented in a separate
patch by means of cross-fading delay lines [110]. Similarly, the ramped phase
block encapsulates the operations necessary to perform a one-pass read of the
wavetable containing the sound file. The subgraph in the lower right corner
represents the linear increase in pitch transposition, obtained by means of the
line UG and used by the harmo unit.