The Kyma Language for Sound Design, Version 4.5

Looping, Feedback
Several Kyma Sounds have internal feedback loops, but you can also create your own feedback loop by
writing into memory with one module and reading out of it (after an arbitrary delay) with another. In the
signal flow diagram, the writer must occur before the reader.
MemoryWriter/Reader
Take a look at the first Sound in this file, the one called write memory, read memory. This is an implementation
of a basic feedback loop which you might draw as:
Source
+
Delay
134
Output
Notice that in the Kyma Sound the last module in the diagram is a MemoryWriter. It writes the sum of
the source plus the delayed source into a delay line named, in this example, recording. Notice that the
Sound called read the memory is a Sample, one of several Kyma Sounds that can read from the sample
RAM of the Capybara. Double-click on read the memory because there is one very important parameter
setting that is easy to overlook. Any time you are reading something from memory that is being written
into memory elsewhere in the Sound structure, you must check the FromMemoryWriter box. Otherwise,
Kyma will search your hard disk looking for the sample named recording. If you check FromMemory-
Writer, then Kyma knows that it has to put the MemoryWriter on the same expansion card as the
Sample that reads the memory. Try playing write memory, read memory to verify that it does indeed
sound like a simple feedback loop.
Actually you could have done exactly the same thing in a much easier way — by feeding the source into a
DelayWithFeedback and controlling the feedback with a fader. But what if you want to insert some kind
of processing in the feedback loop? Open up process in fdbk loop to see an example of this. The fed back
portion of the signal goes through a single side band ring modulator before it is added in with the source
and fed back into the delay line — so the processing is compounded each time around the loop. Try
playing process in fdbk loop to hear the effect.
In write memory, granulate memory, you see an example of using a GrainCloud, rather than a Sample, to
read out of the delay line. The result is a kind of granulated delay line. Try playing it once with the default
source chosen and then switch it over to Live source so you can try singing some long tones into it.
As you probably noticed in this example, the delay line might already have some leftover sound in it
from a previous example. Look at granular read w/zero mem for an example of how to clear the memory
in the delay line before using it. Notice that the input to the MemoryWriter is a Concatenation of a Constant
(with Value zero) followed by the feedback loop. This will write zeroes into the memory on all the
cards first, so the delay lines will be silent at the beginning.
FeedbackLoopInput/FeedbackLoopOutput
What if the modifications you put into the feedback loop are so extensive that they cannot all be scheduled
on the same expansion card as the memory writer and memory reader? To implement a feedback
loop that crosses expansion cards, use the modules called FeedbackLoopInput (writes into the delay line)
and FeedbackLoopOutput (reads from the delay line). Note that these modules can only implement delay
lines of from 12 to 2048 samples long, so if you can get away with using the previous design for feedback,
you should preferentially do it that way, because that gives you a larger range of delay times (down to a
single sample).
Open up basic Feedback in/out example to see a stripped-down illustration of how to set one of these up.
Reading from left to right in the signal flow diagram, the first module is a FeedbackLoopOutput called
read from loop. Notice that its parameters are set so that it reads from a “connection” called feedback
after 128 samples of delay. This is fed into an Attenuator so you can control the amount of feedback, then
it is fed into a DelayWithFeedback to add additional delay if desired. From that point on, it should look