What is a flanging effect?


The flanging effect is as an audio process which combines two audio signals. The second signal is slightly delayed and therefore the combined signal produces a “swirling“ effect.


The history of the flanging effect

The electronic flanging effect derives from the natural acoustic phenomenon that occurs whenever a wideband noise is heard in the mixture of direct and delayed sound. A Dutch mathematician Christiaan Huygens first discovered the flanging phenomenon in 1693. Later on, moving to recent, times F.A. Bilsen and R.J. Ritsma (1969) published their work where they gave the complete history and explanation of the flanging effect. Following that, the guitarist and recording innovator Les Paul was the first to use the flanging as the sound effect in the recording studio. His 1945 flanging system employed two disc recorders. Later, in the 1960`s, producers achieved flanging in the recording studios with two analogue tape recorders and a mixing console.


Tape recorders and flanging


The tape recorders were fed an identical signal. The engineer monitored their combined tape output while putting an occasional pressure on the flange (rim) of one of the reels to slow it down. The use of two recorders was necessary in order to synchronize the overall delay. This delay was introduced by monitoring from the playback head of the flanging recorder. At the 38 cm/second tape speed, the distance between record head and the typical analogue tape recorder introduced a fixed delay of about 35 ms. The precise delay depends on the configuration of the record and playback heads.


Electronic flanging


Electronic flanging uses a continuously varying delay line to achieve the same effect. Consequently, in place of manual pressure to the tape reel, the delay time of an electronic flanger is varied by a low-frequency oscillator. It is usually emitting a sine or triangle shape operating in ranges of 1 to 20 Hz. Flanging can also be described as a swept comb filter effect. In flanging, several nulls sweep up and down in frequency spectrum. Filter peaks are located at frequencies that are integral of 1/Dm where D stands for the delay time.

The depth of flanging is maximum if amplitudes of the original signal and the delay version are equal. The structure is equivalent to a feedforward or the FIR comb filter with a time-varying delay. In practice, most modern flanger effects use IIR or recursive feedback comb structure with a time-varying delay. One can usually be switched between positive and negative feedback.in order to compare which is most effective for a particular sound to be flanged.


Infinite (Barber Pole) flanging


One more interesting technique of flanging effect is “Barber Pole” or Infinite” flanging. This sonic illusion is similar to the Shepard tone effect, and is equivalent to an auditory “barber pole”. The sweep of the flanged sound seems to move in only one direction (“up” or “down”) infinitely, instead of sweeping back-and-forth. Therefore, barber pole flanging uses a cascade of multiple delay lines, fading each one into the mix and fading it out as it sweeps to the delay time limit. Finally, the effect is available on various hardware and software effect systems.


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