Method

Electroacoustic Feedback Loop:

Acoustic Space -> Transducer Inputs -> 
-> Electronic Processing ->
-> Transducer Outputs -> Acoustic Space 

Materials:

Transducer Inputs – dynamic/condenser/contact microphone(s), electric (bass) guitar(s) converting acoustic vibrations into analogue electrical signals.

Transducer Outputs – any device that converts electrical signals into acoustic vibrations. These are usually speakers in stereo or quadraphonic such as a PA, active monitors and/or instrument (preferably valve) amplifiers/speakers but can also include digitally controlled acoustic or electronic instruments that convert MIDI frequency/velocity and Continuous Controller (or OSC) data streams into sound.

Acoustic Space – every performance space has a unique set (a series or musical scale) of natural resonant frequencies, including both harmonic (odd and even) and non-harmonic resonances, physically defined by the architectural form, the transducer frequency responses, as well as ambient air temperature/pressure/humidity and whatever materials are present in that space (e.g.,  the human body, an ~50kg water bag, in sufficient audience numbers can drastically alter the acoustic character of a space).

A simple electroacoustic feedback loop (such as microphone/speaker squeal) demonstrates this natural resonance via the Larsen effect, while electronic manipulation of the electrical signal can be used to suppress resonant feedback (ring out a room) or explore the full spectrum of unique resonant frequencies of a specific acoustic space/time producing standing wave (anti-nodes and nodes distributed within the space) and beat frequency oscillations.

Electronic Processing – analogue electrical signals from transducer inputs can be processed via analogue electronics and/or converted into digital data streams. Multiband EQ filters on the audio inputs can be used to boost or cut low, mid and higher frequency resonances allowing an electroacoustician to navigate (play) the resonant harmonics within an acoustic space. As digital data this audio input stream can be processed in the DSP chain(s) but can also be used as control data. For example a microphone input can be processed in sinusoidal analysis to produce waveform data streams that can then be used as controllers (such as mapping the waveform data to MIDI note on/off or CC, OSC or Max/MSP processes). In this way the resonant frequencies of an acoustic space can be used to both generate the audio input as well as the controllers that parameterize any DSP operations on that input (i.e., surround panning, bussing, volume, any and all FX parameters such as spectral processing and so on). Acoustically derived controller streams can also be used to play digital synthesizers or any other MIDI/CV operated instruments.

Field Recording – Audio inputs are recorded at 24-bit/48kHz along with all mixing and parameter automation data. The resulting field recording is a multitrack audio project containing the raw audio inputs and the automated mixing timeline of the performance which is then mastered in the studio. A room recording of the space can also be used if/when available giving a mix of both internal electronic and external acoustic space audio.

Feedback Mechanisms – Performative, conceptual, electroacoustic, electronic, analogue and digital audio and controller feedback loops within loops within loops.

Results:

  1. The entire acoustic space and everything within it becomes a musical instrument the acoustic properties of which are specific to the space and time of the feedback performance.
  2. The electroacoustic couple (transducer output -> acoustic space -> transducer input) drives both the audio generation and controller parameterization of the electronic processing.
  3. Performative inputs (such as volume, bussing, EQ and any other mixing decisions) navigate through an essentially indeterminate acousmatic soundscape vulnerable to escalating electronic feedback that drives electroacoustic feedback that in turn dynamically changes the electronic parameters of the mix. This performative uncertainty is akin to wandering through a compositional forest of one billion trees at night without a compass in a storm.

Variations on Electroacoustic Feedback

 1. Basic Transducers (electric guitar/microphones)
Transducer input -> EQ filters -> Sinusoidal analysis -> FX Busses -> Transducer output -> Acoustic Space -> Transducer input
Zeitblut Dva and Variation for Electric Bass

2. Acoustics
Microphone input -> EQ filters -> Speaker -> Acoustic space -> Larsen effect -> Acoustic musicians -> Microphone
Variation for Cello and Flute

3. Notation
Microphone input -> EQ filters -> Sinusoidal analysis -> Realtime notation -> Acoustic musicians (human transducers) -> Acoustic space -> Microphone
Work in progress

4. Digital Synthesis
Microphone input -> EQ filters -> Sinusoidal analysis -> MIDI note on/off & CC -> Digital synthesizer -> Speaker -> Acoustic space -> Microphone
Noismaschin#3

5. Analogue Synthesis
Microphone input -> EQ filters -> Sinusoidal analysis -> MIDI CC -> CV -> Analogue synthesizer -> Speaker -> Acoustic Space -> Microphone
Work in progress

Documentation

Recordings (2009 – present)
Variations on Electroacoustic Feedback Vol I

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