Flanger

What Is a Flanging Effect?

The flanging effect is an audio process that combines two audio signals. The second signal is slightly delayed, and 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, giving the complete history and explanation of the flanging effect. Following that, guitarist and recording innovator Les Paul was the first to use flanging as a sound effect in recording studios. His 1945 flanging system employed two disc recorders. Later, in the 1960s, producers achieved flanging in the recording studios with two analog 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 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 the recording head and the typical analog 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 on the tape reel, the delay time of an electronic flanger is run by a low-frequency oscillator. It usually emits a sine or triangle shape operating in 1 to 20 Hz ranges. Flanging can also be described as a swept comb filter effect. In flanging, several nulls sweep up and down in the frequency spectrum. Filter peaks are located at frequencies integral to 1/Dm, where D is the delay time. The depth of flanging is maximum if the 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. 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 to compare which is most effective for a sound to be flanged.

Infinite (Barber Pole) Flanging

One more interesting technique of the 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 effects systems.   

Additional Resources & Source Texts

•   Flanging