If you had a remote control and could joystick the car back and forth with the horn blowing you'd hear the pitch increase every time the car got closer, and decrease each time it moved away. If you have a Time Modulator and turn the Time Delay knob back and forth you'll hear the same thing. In fact, it sounds exactly the same. Steve got pots with custom tapers, so that natural sounding doppler and flange effects could be produced by manually sweeping the knob from end to end. (Of course you could do "automatic" flanging by using the VCO, but manual mode was carefully optimized so that the operator could "play" the Delay control in a musical way, timing the sweep to fit the length of a chorus, a solo, etc.)

The day my uncle Leo or Larry Levine pushed the wrong button and discovered flanging, a kind of Doppler signal was produced by the additional deck, which, owing to worn mechanical parts and Murphy's law, would inevitably have been running at a slightly different speed. The outputs of the two decks were summed, with a little time delay on one deck. The delay caused cancellation at certain frequencies, and Larry or Leo, or whoever could sweep the cancellation -- the pitch of the jet plane effect -- by letting his finger gently rub the reel flange, and then maybe pushing the flange to speed it up a tad. This produced a swept comb filter effect. The harmonics and overtones were "notched" up and then maybe down. It sounded just like a jet plane taking off from stage left to stage right. The jet plane is a good analogy because it's sound, a little like pink noise, contains a smorgasbord of frequency components that, combined with Doppler, create a kind of flanging sound.

Itchycoo Park came and went, tape flanging was a neat engineer's trick, but it tied up two tape machines and was way unwieldy. In 1971, new company Eventide released the PS101 Instant Phaser, a black box that roughly approximated flanging. It's anemic 20 db null (vs. the 35 db from traditional tape machines flanges) wasn't too impressive but the real problem was: phasing is just a coarse approximation of flanging. Eventide released the FL201 Instant Flanger in 1976. It was a great improvement over the Instant Phaser. (Was this the first "flanger in a box"?)

Conceptual difference: flanging is about time delay, phasing is about phase shift. Phase shift is simpler and cheaper to implement, but is limited to 180 degrees of delay, and doesn't sound as good. Unlike phase nulls, flange nulls are harmonically related and sound more musical. For example, 440 Hertz "A" above middle C has harmonics at 880 Hz., 1320, 1760, 2200, etc. With a delay of 136 milliseconds the fundamental and all odd harmonics will cancel out, leaving only the even harmonics. Compared to phasing, flanging produces more frequency nulls. Flanging is more difficult to achieve, but is more pronounced and natural sounding.

Of course the MTM was a flanger, not a phaser. It was distinguished by the extreme depth of its nulls -- up to 85 db, far more than tape deck flanging could accomplish. This was accomplished by creating the effect within a dbx type II compression/expansion loop, which doubled the intensity of the nulls, producing an amazing sound that had not been heard before.

Positive, negative, and through zero flanging

The effect that Larry Levine or uncle Leo discovered and used in The Big Hurt was positive flanging. The dry and delayed signals were combined in phase. With very short time differences between the two decks, cancellations occurred at notches in the higher frequencies, producing the jet plane effect.