Feedbacker V2 — an updated feedback drone machine

I originally wrote Feedbacker for the Euroburo factory set. Inspired by the Tilde Elektriske Fjaerlett (I’ll do a comp when I get mine in my early 60s) and some ideas from no-input mixing, Feedbacker is a feedback loop that can process external audio, but in its original conception produces feedback soundscapes and drones from nothing more than the very minimal noise floor of ZOIA, amplified again and again in its feedback loop, until it becomes a sound source for the patch.

Just a word of warning: this patch uses feedback as a sound source. Part of the signal path is a limiter (compressor set to 1:infinity ratio). The patch is generally under control, because of this limiter. But if you set the compressor threshold too high, the feedback can get loud, fast. (I would recommend making changes to the compressor threshold slowly.)

A quick rundown of changes in version 2:

— While original was designed for Euroburo (and I think still ideally suited for that implementation), a number of additions have been made to make the patch better suited to the pedal format of ZOIA: the user buttons (Reverb freeze and Filter Q change) have been replicated in stompswitches; a MIDI option has been added, which allows you to control the ring modulator oscillator frequency via MIDI and route an internal envelope to any of the feedback level, low-pass filter frequency, or high-pass filter frequency.

— Processing external audio via the patch has been improved.

— The CV assignments have been changed: They now control feedback level, ring oscillator frequency, low-pass filter frequency, high-pass filter frequency. (The last three can track V/oct when their attenuverter controls are set to maximum.)

— No more clicking when changing the filter Q control. (In previous versions, this produced an annoying click as all the multi-filters changed parameters at once, which spiked the CPU. Delays have been added, so the change occurs at a speed the CPU can keep up with — still very fast.)

— A resonance control was added for the low-pass and high-pass filter.

— The Euroburo inputs and outputs were swapped for ZOIA input and output modules. Mostly, because this gave me a “cheap” level control, in terms of the output gain control of the output module. This module is found on the second page of the patch and has been starred.

— The reverb freeze has been improved, so it now gradually tapers off when released.

Signal path:

Audio in –> parametric EQ (8 bell filters linked in series) –> aliaser –> low-pass filter –> high-pass filter –> limiter (compressor set to 1:infinity ratio) –> feedback level (make-up gain) –> ring mod mix (ring mod is combined with the output of the feedback level VCA) –> plate reverb (100% wet) –> audio output
Plate reverb –> parametric EQ

Because the entire patch is one big feedback loop, all of the controls are highly interactive.

Controls:

User buttons/stompswitches:

Left user button/stompswitch — REVERB FREEZE. This cuts off the input of the reverb and extends its decay to infinite to hold sounds from the feedback loop

Right user button/middle stompswitch — FILTER Q (also replicated on the control page). This adjusts the filter Q/width of the bell filters which form the parametric EQ. As this is adjusted, the UI button on the control page will change from lime (widest Q) to pink (narrowest Q). The widest Q will have more distortion/gain, as the bands overlap more, while the narrowest Q will essentially produce sine waves at the frequencies of the parametric EQ (making the patch into something of an additive synthesizer)

CV inputs:

CV 1 (0-5V) — feedback level w/attenuverter control located above the input

CV 2 (0-10V) — ring modulator oscillator frequency w/attenuverter control located above the input (when attenuverter is fully open, the input will track V/Oct)

CV 3 (0-10V) — low-pass filter frequency w/attenuverter control located above the input (when attenuverter is fully open, the input will track V/Oct)

CV 4 (0-10V) — high-pass filter frequency w/attenuverter control located above the input (when attenuverter is fully open, the input will track V/Oct)

Control page:

The top row is used to tune the FREQUENCIES of the parametric EQ. By default, the filters are tuned to notes from A minor scale across ~6 octaves. But those were just some settings I tried and liked; changing/retuning the filters can have a drastic impact on the output of the patch.

The second row is the GAIN controls for those filters, with -/+ 40 dB of gain available per band. Gain at some frequencies (highly dependent on the filter Q settings) can compound over time — the output of the patch tends to settle into meta-stable conditions, but it may change unexpectedly at times, subtly or not so subtly.

The third row are pushbuttons labeled TEMPORARY MAX. These allow you to “play” the patch, if you want, by temporarily maxing out the gain (+40 dB) of a specific band. Depending on what the gain is initially set to in the row above, this may have more or less dramatic effects (going from negative gain to +40 dB will be pretty noticeable, going from +35 dB to +40 dB may not be).

On the fourth and fifth row are some global controls.

FEEDBACK LEVEL sets the gain attenuation/make-up gain for the patch, post-limiter. It works in conjunction with the COMPRESS THRESHOLD control, also on this row, to control the output level of the patch, but also the timbre, with more gain = more distortion/feedback.

The REVERB DECAY sets the decay of the 100% wet plate reverb used in the patch. More decay will wash out some of the sounds, as well as add gain to the feedback path.

The RING MOD FREQ determines the frequency or pitch of the ring modulator’s sine wave oscillator. This control is bipolar and can go into negative frequencies. As the ring mod drops below audio range, it has an effect similar to a tremolo, which can add movement to a patch. The RING MOD MIX controls the mix of audio that passes through the ring modulator.

The FILTER Q button is discussed above, in the user button/stompswitch section. But it very important to the timbre of the feedback.

The DRY LEVEL determines the dry level of audio that passes through the patch. The dry signal is stereo. The wet signal is summed to mono, then output through the stereo plate reverb.

The ALIASER FREQUENCY controls the sample rate reduction. This can be used to totally massacre sounds, or more subtly to add different harmonics and bell-like qualities.

The LP-HP RESONANCE control determines the resonance of both filters. Adding resonance can produce tones at that filter’s cutoff frequency.

The LP FREQUENCY control for the low-pass filter is bipolar, allowing the low-pass filter to drop into sub-audio frequencies. (This has some useful applications; see the end of the demo video for some more melodic applications of the patch.) In many cases, I “disable” the low-pass filter by setting it to its highest frequency (well above the audio range).

The HP FREQUENCY control for the high-pass filter control is also bipolar. In many cases, I “disable” the high-pass filter by setting it at its lowest frequency (well below the audio range).

The two filters can do quite a lot to “sculpt” the output of the patch, when used separately or in conjunction.

2 comments on “Feedbacker V2 — an updated feedback drone machine
  • del-uks on said:

    I am also on the endless waiting list to be able to order this famous Tilde Elektriske Kretser Fjærlett one day (maybe, I hope)… last I heard, Kristoffer estimated a waiting time of about 5 years! :-(
    In the meantime, I’m looking forward to try this patch… Merci beaucoup Christopher Jacques pour ce formidable cadeau ! 🙏🏽🙌🏽
    I don’t own a ZOIA Euroburo but the “simple” one in pedal format… but since this patch is a kind of “homage” to the Fjaerlett, would it be possible to assign the 8 bell filters in MIDI CC, as well as other functions (FEEDBACK LEVEL, REVERB DECAY, RING MOD FREQ, FILTER Q, ALIASER FREQUENCY, LP-HP RESONANCE, LP FREQUENCY & HP FREQUENCY) to make it compatible with the AtoVproject – 16n controller which has 16 high-end Alps faders ( https://atovproject.de/products/16nrework ).
    If so, I think I can definitely cure my obsession (and frustrations) induced by waiting for the Fjærlett. ;-)
    Thanks again Christopher Jacques for this fantastic patch, as well as for the many others that make the ZOIA an essential part of my setup ! 🙏🏽

  • christopher-h-m-jacques on said:

    If I am being honest, I don’t really expect to ever get my Fjaerlett. I’ve been on the waitlist, as I’m sure you have, for almost three years now, and I do not see a lot of them making their way out into the world. But this patch is available today!

    (And it has been available for about a year and a half — you might want to look through the Euroburo factory patches at some point. Mike Moger — meanmedianmoge — and I put a lot of effort into them, and there are some interesting results that I think get overlooked. They are designed for the Euroburo, but any Euroburo patch can be adapted to the pedal format and vice versa. Most will run on either platform without any issue, except the fact that some of the I/O support may be different/absent and may need to be modified/added/replaced.)

    You can make any of these assignments using the starred parameters/MIDI learn option — if you’re not familiar with it, there’s more information on it in the manual. Part of the reason I create control pages for my patches — beyond just the convenience of consolidating the useful parameters — is so that the parameters internal to the patch are readily accessible for starring/MIDI learn or connecting to a CV/expression module. So, you can just star the controls on that page that you want to assign and then go through the MIDI learn process to connect them to your 16n.

    The patch will work just fine on ZOIA, as well as Euroburo. I honestly may have originally written it on ZOIA (there were some periods during Euroburo development/alpha-testing where the firmware was a mess, so I worked on patches on my ZOIA and then transferred them to the Euroburo to complete them).

    The only hesitation I would have about mapping the patch to your 16n is that the bell filters are made from multi-filter modules. The multi-filter is quite complex in its design, and because of this, it consumes a lot of CPU — momentarily — when its parameters are adjusted. So if you try to adjust too many of the filters at the same time, you may encounter CPU clipping.

    I hope that is helpful. Thank you for the kind words!

    Best,
    Christopher

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