Feedback Cell

Brain Dead Ensemble

Thu, 13 Dec 2018 00:00:00 +0000

Brain Dead Ensemble grew from a performance we did at NIME 2017 in Copenhagen with Thor Magnusson, as ‘2FCT’. Thor plays an instrument that he designed, called the Threnoscope.

The Threnoscope is a spatialised drone instrument that is played using live coding. Drones are programmed to move around a circular path, and the instrument is typically diffused through four or more speakers. With 2FCT, we set up the Threnoscope so that in addition to a multichannel speaker setup, the two feedback cellos also received signals and became part of the diffusion system. This had some interesting effects in performance, where a feedback cello will become saturated by a drone as it passes through, changing the dynamics of the instrument. It links the instruments together into a larger shared instrument.

Following the NIME gig, Thanos built a double bass version of the feedback cello, and joined us to form Brain Dead Ensemble.

We’ve played three gigs so far at: Emute Lab 0 in Brighton, ICLI in Porto and Spirit of Gravity in Brighton. We have also been recording, and will be releasing something very soon.

Brain Dead Ensemble are Feedback Cell + Thor Magnusson on Threnoscope and Thanos Polymeneas-Liontiris on Feedback Double Bass

A Patch Explained

Sat, 21 Oct 2017 00:00:00 +0000

I’m really enjoying playing this patch; it has a huge range of dynamics and sensitivity, and also tremendous subtlety in places. The range of sounds is so wide that I didn’t need any other patches for our gig at EarZoom. In fact, I think I’m going to need to play it for a while so get a really sense of how it works, it feels like i’m only just scratching the surface of the possibilities. I’m getting an intuitive understanding of what it does through playing the instrument, but i’m only just getting a handle on what it does logically. I’m going to try and explain how it works.

This code is written in SuperCollider. It receives and augio signal from each string, and outputs two audio signals, one for the speaker and one that is sent to both transducers.

In the first section lines 2-5, functions are defined for reading the positions of the knobs on the control board. ~m maps the value into a linear range, and ~ml maps it into an exponential range.

In the second section lines 11-13, the audio signals from the four strings are read and scaled, and then mixed together. The individual levels of the signals are controllable using knobs 1-4.

The third section, lines 18-27 is the main part of the patch. Line 19 reads in the signal created earlier that is a mixture of the signals from the four strings. The code between 20-23 is an amplitude envelope follower. This follows the peak of a signal. The graph below shows the amplitude follower processing a test signal with various settings, reflecting the maximum values in the patch of 0.03 for attackTime and releaseTime.

Raising attackTime makes the follower less sensitive to the input, and raising releaseTime makes the effects of the input last for longer.

The patch runs four amplitude followers, one for the signal from each string. Within this, the levels of the string signals can be modified individually using knobs on the cello, and the attack and release time can also be changed from the control knobs. These signals are mixed together by taking the average of the four signals using the mean function, and the result is stored in amps.

Line 24 is taken from another patch, and in itself can provide quite a wide range of complexity. It uses the Integrator UGen which implements the formula out(0) = in(0) + (coef * out(-1)); it’s a very simple low pass filter. The graph below shows what the Integrator produces when fed the absolute values of the test signal, with coef set to 0.98, 0.90 and 0.85.. The test signal is scaled by a factor of 10 to make it more visible.

The patch then calculates the reciprocal of the output from the Integrator, and multiplies this by the original signal. The stages of this can be seen in the time series below:

It can be seen from the last time series that this line of code permanently saturates the test signal; if the signal is quiet it raises the gain, if it’s loud then it squashes the signal. The result pushes constant energy through the system, no matter the level of the input.

The patch has now calculated two signals amps and wi. Finally it combines these together in line 25, using a cross-fader, XFade2. One of the parameters for this cross-fader is pan. When this is at 1, the signal w will play; this is the unprocessed sound of the strings. When pan is set at -1, the signal wi will play; this is the saturated sound made by the Integrator. At points in-between -1 and 1, we get a mixture of these signals. The pan is controlled by the amps signal, within a range set by one of the knobs on the cello. This mapping has the effect that as the sound in the feedback system becomes louder, we get a higher mix of the natural unsaturated sound, giving two opposing systems with play against each other. At default we have the loud saturated sound, but if this rises above the threshold then the natural sound of the cello is mixed in, bringing the overall volume down (unless the system is feeding back loudly, in which case the system will stay in this state). At certain settings of the mapping range, the system starts to oscillate between the two states of saturated and unprocessed sound.

From a players experience, this patch gives a really wide range of sound. At different settings, you can have the ‘natural’ sound of the feedback cello, or the saturated version, or oscillations between the two. It’s possible to set up the system to hang in a delicate balance between the two states, such that if you lightly mute a string then it jumps into another state. It can move between very gentle feedback loops into very aggressive walls of noise. Interestingly, this complex behaviour comes from surprisingly little code, with fairly straightforward UGens; the complexity of the instrument itself mixed with these small patch provide a really expressive range of playing modes. I keep discovering new modes and behaviours of this patch, and there are probably plenty more to be revealed.

Chris' System, October 2017

Sat, 21 Oct 2017 00:00:00 +0000

(1) Cello: Musima (East German, cheapish on ebay, and well-built)

(2) Speaker: Monacor 50W

(3) Amp: Sony car amp, 50W * 4

(4) Soundcard: something with 4ins, 2outs

(5) Pickups: Cycfi Nu-modular

(6) Microcontroller: Teensy 3.6

(7) Laptop: Macbook Pro, or anything that runs SuperCollider

(8) High transducer: Vidsonix Phantom

(9) Low transducer: Vidsonix Ghost

Power: 5V supply for pickups, 12V for the car amp, using a PC ATX power supply. The control board has 15 knobs and 7 switches.d

IAA Day 2

Mon, 13 Feb 2017 00:00:00 +0000

We refined the new transducer brackets, using single clamps to mount the transducers, giving much more flexibility in placement. The photo below shows two different types of transducer mounted on the cello.

The brackets were laser cut from plywood, and we used spots of hotglue to get extra grip. This was especially important for the Phantom transducers which weight around 1.2kg.

We began to look at control panels, and added sliders to Alice’s instrument.

IAA Day 1

Mon, 13 Feb 2017 00:00:00 +0000

Up to this point, the cellos used Vidsonix Ghost transducers (along with a 50W speaker). We wanted to try out the larger Vidsonix Phantom transducer, as it has roughly an extra octave of lower frequency response. The challenge was fitting them onto the instruments as they are much heavier. We began by experimenting with placing the cello’s spike onto the transducer, which gave some great results.

We also designed a new style of mounting bracket for the transducers. Previously we use a plywood brace, clamped across the front of the cello. This worked well but was cumbersome. We experimented with the best points to mount the new transducer, and decided that close to the edge of the cello sounded best. The edge of the cello isn’t a very resonant point, but for a feedback cello this is great as it gives a more complex path from the transducer to the strings, making a richer sound.

Live in Iceland

Sun, 12 Feb 2017 00:00:00 +0000

To begin the week we played a feedback trio at Mengi, joined by Ingi Garðar Erlendsson on Þránófónn.

Trios

Tue, 13 Dec 2016 00:00:00 +0000

Beside Feedback Cell gigs and Brain Dead Ensemble gigs, we’ve been lucky to have opportunities to play with quite a range of other improvisers in the last year couple of years.

In early gigs, whilst I enjoyed the distinct sound of the feedback cello, I was secretly a little concerned it may be a one-trick-pony. Yet even in the first year each time we played, we’d discover new terrain - even with my set up, which is completely analogue. Over the last couple of years, we’ve had opportunities to play in ever widening musical contexts; each time we discover news sounds, new gestures, new nuances. As a cellist it’s It’s pretty exciting and inspires further instrument refinement.

Resonator Piano Trio (Sept 2016)

Our first workshop back in ICLI 2016 was held in parallel with Andrew McPherson’s fearsome Magnetic Resonator Piano (MRP), played by Kate Ryder. In the workshop concert, despite extreme technical issues (my amp was blown up by the first act), we got a little taste of the MRP and Feedback Cello duo sound world. Later that year, we took the opportunity to play as a trio with Roger Redgate on violin at magnetic attraction, a doctoral showcase organised by the students on the XXXX course at Queen Mary’s University.

Playing a trio with the MRP and electric violin made me really appreciate how even the earliest version of the instrument managed to bridge the acoustic string and hybrid resonator sound worlds. The violin was amplified locally, the cello through it’s built in speaker and the MRP purely acoustic, yet our sound merged to the point that the origin was ambiguous - gestures originating from one player seemed to terminate in anothers instrument.

https://soundcloud.com/roger-redgate/rr-with-kate-ryder-magnetic-resonator-piano-alice-eldridge-feedback-cello

https://vimeo.com/185694346

Magnetic Attraction. An evening of music performed on the magnetic resonator piano by Kate Ryder. The programme features pieces written especially for the instrument and improvisations with Alice Eldridge (amplified cello) and Roger Redgate (violin/fx pedal).

Multiphonics in free jazz trio

Soon after I decided to take the feedback cello to Fete QuaQua. Curated by stalwart of Free Improv John Russel, this is an annual event of joy where John invites wonderful musicians from around europe to play in varying combinations over 3 nights. Here’s a little clip of a set with

Bowed metal, electronics & fiddle harmonics

Time, space & power in hybrid ensembles

Live @ Algomech 2016

Tue, 15 Nov 2016 00:00:00 +0000

We experimented with various bits of hardware to influence the sounds of the cellos: clothes pegs, laser printer parts, screwdrivers. The pegs work well when placed on individual strings just above the bridge; as the strings vibrate, they vibrate themselves and react against the motion of the string. We both used contact mics at the start of the gig, which were connected directly into the transducers on the cellos. Playing the cellos with these is a bit like probing them with stethoscopes to find live points - felt like a cruder, sonic version of the analyses Hans Johansson carried out, to determine the nodes of oscillation on the instrument bodies.

Not surprisingly the quality of the contact mics makes a huge difference. Cheap piezo’s mounted on wood are super sensitive to positioning: a mm is the difference between a brutal (maybe not in a nice way) shriek and silence; somewhere in between sits a sweet spot of beautiful tones. The more considered build of the JRF contact mics, on the other hand, have a much wider range of acoustic joy. Great satisfaction is to be had in dynamically probing the instrument in this novel gestural way. I fell into 3 main approaches: rapidly scan the front and back surfaces to pick up changing responses across the body, which gives a kind of souped up Australian magpie warbling. Moving one slowly across the front surface whilst varying the pressure of another on the bridge; this closes and opens another feedback short circuit in the cello, and affords control-able pitched, pulsing. Finally, varying the distance between cello body and contact mic by holding it further into your palm and cupping fingers up and down creates a super satisfying sub-bass.

3D print tag

Fri, 01 Jul 2016 00:00:00 +0000

Halldor’s visit is fixed, with the power of ERASMUS, he’ll be coming over for a week before ICLI. In the spirit of NIME, we’ll have not only a performance, but a 2day workshop to run with the instruments. Deadlines are good, right?

I’d never thought about the power of 3D printing for remote instrument building collaborations. Over the last few months we’ve scoured eBay & Gumtree for some cellos and started buying the core components for the cellos. What’s great about 3D printing, is that we can start design iterations even before Halldor gets here – essential as we’ll have just one week.

Armed with measurements of the cello fingerboards, Halldor sent over some .stl files, which we printed in the Engineering dept. At this stage, Halldor’s quite keen to try and make a non-invasive version. We’re pretty open to hacking them a bit. Great to think about this tho, for other people who might to try.

The first things to think about are how to fix the pick-ups under the strings, where to place the speaker and how to fix it to the cello.

Pick-up Brackets

#1 pick up fingerboard bracket

This fitted Chris’ cello really well

but needed a tweak for mine

With a solid connection onto the finger board, we can fit some adjustable arms with cups to hold the pick-ups, to allow control over the distance from pick-ups to strings.

Speaker placement

The next decision was where to fit the speakers. Describing our plans to fit a speaker inside the body of the cello illicited a sharp intake of breath from many luthiers. But on the advice of those who got what we were planned, we decided back lower left would be the best placement to minimise stress and prevent tearing the body.

Planned speaker placements

Speaker fitting

Cello backs curve in both directions, so in order to get a nice tight coupling between the flat, metal speaker and the cello body, Halldor came up with the idea of cutting some wooden collars which can be shaped to fit the cello back. We’re thinking maybe in rowan, or spruce. The speaker faces inwards on the Halldorophone, but we’re not bothered about phase here. Our feeling is that the logistical desire to be able to fit the cello in a standard case without having to remove the speaker is the main constraint – so the cone could just face outward, the cello body acting like a speaker cabinet.

3D mock up: a wooden collar can be machine-cut, then hand sanded to fit the curvature of the cellos. This will both maximise acoustic coupling and help reinforce the hole we’ll cut in the cello body

The idea is that the speakers can be bolted into the cellos, meaning they can be removed if necessary (e.g. if blown), but become a permanent fixture. Side view showing collar fitted to cello back, receiving speaker

Using slightly less sophisticated design tools, we also discussed the idea of having a plywood ‘hole-reinforcer’ on the inside, to give extra support for the bolt holes. I’ve never bolted things onto a cello before, or cut one open, so not really sure how thick the wood is on the body here; we want to make sure the weight of the speaker doesn’t rip through it. That would be bad.

Side sketch showing planned ‘hole-reinforcers’ to ensure house and support internal bolts

Cello time

Mon, 04 Jan 2016 00:00:00 +0000

I heard about Halldor Ulfarssson’s Halldorophone (above), a cello-like feedback instrument from colleague Thor Magnusson. Watching a beautifully shot a video of Hildur Guðnadóttir playing one, I had a slightly childish feeling of ‘wanting one’. Seeing her play it, I felt it might answer an itch that had spawned my PhD, and never quite been satisfied: wanting an instrument which was playable, to a degree, but also with a bit of a mind of its own. A cello-y system for negotiating music-making.

So I propositioned Halldor after a talk he gave at Sussex at the end of 2015, and followed up with an email:

… two days later he responded positively:

… and then Chris expressed an interest in getting involved too: