(8.D.2.7) Feedback Example

Below is an example of a system using feedback. This system creates a series of echoes by adding to the audio a delayed, scaled down copy of itself. The wire from the output of the ScalerV2 module to the top input of the Adder module is feedback:

Build and run the system to see the build error shown above. The problem occurs because Audio Weaver is unable to determine that there is feedback in the system; this must be manually indicated.

Right-click on the wire at the output of the ScalerV2 module, select “Feedback,” and then specify the feedback properties. In this case, the feedback wire is stereo and has the properties shown below.

The system can then be redrawn and the feedback wire will be marked in blue.

A simple addition of an ImpulseMsecSource and Interleave module to this system allows for an excellent demonstration of the echo property caused by the feedback:

With the impulse set to a period of 1000 msec, the delay module set to 100 msec, and the first scalar module set to -3dB (the second scalar should be set around -10dB to lower the level – remember, sources are very loud), the echo should be very clearly audible. Those settings can be changed to explore their effects on the echo, but be warned that if the first scalar’s gain surpasses 0dB, it will cause instability as it will increase the level of the signal that eventually feeds back into itself! A gain lower than 0dB will cause the echoes to gradually fade. The multiplexor can be used to switch between the impulse source and sample audio.

A more sophisticated example of feedback can be seen in the Audio Weaver Reverb example, found with the path: Examples/Designer/Float/FX/Reverb_Example.awd:

Double-click on the Reverb subsystem to open it and scroll to the right to see a very large (8-channel) blue feedback wire used to create the semi-random echoes that constitute the reverberation: