Acoustic feedback
As acoustic feedback or feedback is called an audio effect, this does that a sound receiver (eg. As a microphone ), which via for example, a his own amplified output speaker is reproduced, which recommences. The signal received again is continuously amplified and reproduced. The arrangement forms an oscillator . The best-known consequence is a characteristic whistle that is usually perceived as shrill. In the real sense, the feedback is only the cause that makes the oscillation possible. In a broader sense, however, the sound effect itself or the occurrence of an oscillation is also referred to as feedback . Feedback can be undesirable or it can also be a desired effect as a means of sound formation .
General
The feedback is based on the Barkhausen stability criterion named after the German physicist Heinrich Georg Barkhausen in 1921 and originating from him . It is a mathematical condition that a linear electronic circuit begins to oscillate . It is based on his formula of the self-excitation of the system sound pick-up - amplifier - loudspeaker. The signal from the loudspeaker becomes the input signal on the microphone (or another device that acts as a sound transducer , such as an electric guitar) and is thus amplified again and again. For a long time, feedback was considered, in addition to distortion, to be an absolutely avoidable interference effect when recording music in recording studios . Especially with upcoming live concerts from 1962 onwards, this feedback was also an undesirable disruptive effect, mostly caused by the high volume level of the amplifiers. In recording studios, the placement of sound sources or the use of sound absorption devices ensured that direct sound was avoided and this disruptive effect was suppressed. The effect is usually undesirable with vocal microphones. It is avoided by the directional characteristics of the microphones and speakers as well as their alignment, see monitor box . Furthermore, the microphones should be positioned as close as possible to the sound source in order to be able to keep the amplification low. Unused microphones are switched off or turned down. If the microphone and speakers are inadequately positioned, the stability criterion is violated; A theoretically necessary triggering of the oscillation cannot be prevented in practice, since even the basic noise of the electronics and the air , no matter how small, is sufficient.
In the case of feedback from the loudspeaker to the microphone, the frequency of the oscillation that builds up essentially depends on the resonance properties of the room in which the sound transducers are installed and is therefore difficult to control. The situation is different with feedbacks, the signal path of which leads through a musical instrument - a typical example is the path via the electric guitar. The frequency here essentially depends on the resonance properties of the instrument, which can be easily influenced by the player - in the case of the electric guitar, for example, by grasping and changing the distance to the loudspeaker; as a result, the feedback has developed into a deliberately used musical effect, which is described below. The technical basics, however, are explained in more detail in the article feedback under sound engineering .
Feedback in rock music
Johnny Watson's Space Guitar (Federal # 12175) was recorded on February 1, 1954 with reverb and feedback effects from the guitar and is considered to be the first feedback to be pressed onto a record. The Beatles were probably the first rock group to consciously use feedback as an audio effect. In the intro of the Beatles hit I Feel Fine , recorded from October 18, 1964, two seconds of feedback can be heard. In this song they first used amplifier feedback. Called an "electronic accident" by the press, John Lennon made a conscious use of amplifier feedback. Paul McCartney played an A on his electric bass that jumped over to Lennon's Vox AC30 amplifier. During the recordings for the third single Anyhow, Anywhere by the rock group The Who on April 13 and 14, 1965 in the London IBC Studios, feedback in the instrumental part during the final mix was overheard by producer Shel Talmy and ended up on the single. In May 1965, the single was frowned upon by acoustics aesthetes and reached number ten on the British charts . On October 13, 1965, this effect was again used extensively by The Who when recording the backing track for the hit My Generation in the IBC studios. Pete Townshend's Rickenbacker guitar triggered the feedback effects with its pickup, especially in the outro . This outro presents electrical chaos with objects thrown against the drum kit and the pickups turning on and off. After its publication on October 29, 1965, there was great excitement among experts and the public. The Who achieved the best chart placement of their career with second place. The album of the same name contained another song called Out in the Street with deliberately used feedback. The Who thus became a model for legitimate feedback as sound design in rock music , applied as an extended technique .
Jimi Hendrix used the feedback excessively, especially during live performances, and even perfected melody-leading feedback noises. This is particularly evident in his interpretation of the Star-Spangled Banner on August 18, 1969 at the Woodstock Festival . Depending on how the guitarist positions himself in relation to his amplifier, it is possible to influence the pitch of the feedback. His feedback, wah-wah, and fuzztone- loaded solos became his trademark. Another extensive and controlled feedback came from the Shel Talmy-produced group Creation in their November 1966 hit Painter Man in the outro.
The second album by The Velvet Underground , White Light / White Heat from December 1967, is particularly noticeable due to the excessive use of distortion and feedback. In July 1975 Lou Reed , ex-member of the Velvet Underground, released the double album Metal Machine Music . It consists only of guitar feedback and distortion, and was seen as an attempt to break away from his recording deal and / or his then manager (who he felt gagged both financially and artistically by). Sonic Youth's distinguishing feature from 1982 on are guitar feedback in particular.
literature
- R. Beckmann: Manual of PA technology, basic component practice. 2nd edition, Elektor-Verlag, Aachen 1990, ISBN 3-921608-66-X .
- Uwe Breitenborn: Acoustic feedback. On the history and structure of a style-forming effect in contemporary music. Arkadien-Verlag, Berlin 2009, ISBN 978-3-940863-08-9 .