Flange comes from one of the early methods

Flange

Flanging is an audio effect produced by mixing two identical signals together,
one signal delayed by a small and gradually changing period, usually smaller
than 20 milliseconds. This produces a
swept comb filter effect: peaks and
notches are produced in the resulting frequency
spectrum,
related to each other in a linear harmonic
series.
Varying the time delay causes these to sweep up and down the frequency
spectrum. A flanger is an effect
unit that
creates this effect.

First, the input signal is
divided into two independent signals, one of which remains unchanged, while the
other enters the delay line. In the delay line, the signal is delayed by 5-15
ms, and the delay time varies according to the signal of the low-frequency
oscillator. At the output, the delayed signal is mixed with the original
signal. The low-frequency generator modulates the delay time of the signal. It
produces oscillations of a certain shape, ranging from 3 Hz and lower. By
varying the frequency, shape, and amplitude of the oscillations of the
low-frequency generator, a different output signal can be obtained.

Part of the
output signal is fed back to the input and to the delay line. As a result of
the resonance of the signals, a flange effect is obtained. The phase of the feedback
signal is sometimes inverted, thereby achieving an additional variation of the
audio signal.

In contrast, flanging relies on adding the
signal to a uniform time-delayed copy of itself, which results in an output
signal with peaks and troughs which are in a harmonic series.
Extending the comb analogy, flanging yields a comb filter with regularly spaced
teeth, whereas phasing results in a comb filter with irregularly spaced teeth.

As an audio effect, a listener hears a
“drainpipe” or “swoosh” or “jet plane” sweeping
effect as shifting sum-and-difference harmonics are created analogous to use of
a variable notch filter. The term “flanging” comes from one
of the early methods of producing the effect. The finished music track is
recorded simultaneously to two matching tape machines, then replayed with both decks in sync. The playback-head output from
the two recorders is mixed to a third recorder. The engineer slows down one
recorder by lightly pressing a finger on the flange (rim)
of one of the playout reels. The “drainpipe” or subtle
“swoosh” ‘flange flango’ effect “sweeps” in one direction,
and the playback of that recorder remains slightly behind the other when the
finger is removed.

The original tape-flanging effect sounds a
little different from electronic and software recreations. Not only is the
tape-flanging signal time-delayed, but response characteristics at different
frequencies of the tape and tape heads introduced phase shifts
into the signals as well. Thus, while the peaks and troughs of the comb filter
are more or less in a linear harmonic series, there is a significant non-linear
behaviour too, causing the timbre of tape-flanging to sound more like a
combination of what came to be known as flanging and phasing.

Distortion

Distortion
is a sound effect achieved by deformation
of a signal by its “hard” amplitude limitation, or a device providing
such an effect. Sometimes this term refers to a group of similar sound effects
(overdrive, fuzz and others) that realize nonlinear distortion of the signal.
They are also called “overload” effects, and the corresponding
devices are “distortors”.

The
distortion effect, as a component, is present in synthesizers, effect
processors and computer programs for sound processing.

A
large number of harmonics arise in the spectrum of the distorted signal. Each
harmonic represents a sinusoidal oscillation, with a frequency greater and a
multiple of the fundamental frequency. Harmonics of higher orders are already
outside the sound range and have a small amplitude of oscillations, so they can
be neglected. In accordance with the multiplicity, the harmonics are divided
into even and odd. Even harmonics consonant with each other and with the basic
tone, thereby giving the instrument’s timbre volume and depth. The frequency,
for example, of the third harmonic is three times higher than the frequency of
the fundamental tone and corresponds to a note lying from the fundamental tone
at a distance of a fifth through an octave. In principle, this harmonic can be
called a consonant basic tone, but when playing several notes simultaneously,
it can be discordant with another basic tone and its harmonics. Thus, the odd
harmonics of higher orders are less musical and create “mud” in the
sound.

Low
notes sound “overloaded” high. In high sounds, harmonics will
increasingly go beyond earshot, while at low frequencies they are within the
frequency range. It should also be borne in mind that the vibrations of the
strings are not pure tones (unless the natural flajulets are as close to them
as possible) and are themselves rich in harmonics. That is, a complex signal is
subjected to distortion and its harmonics generate their additional harmonics.
Obviously, for sounds produced by thick strings, there are more distinguishable
harmonics, and, accordingly, more secondary harmonics generated by them.

There
is also such a phenomenon as intermodulation: two simultaneously sounding notes
cause distortion to produce another sound, determined by the difference in
their frequencies. In the case of two notes, this sound is in harmony with the
two basic notes, but three notes form three pairs of notes and generate three
secondary sounds introducing dissonance.