The phaser is a delay time-based effect that is used in the pedalboard of a rig to alienate instruments (usually guitar, but also keyboards or bass, rarely drums) and the human voice as a sound effect . It is generated by a filter with several cancellations and increases in the frequency spectrum, the frequencies of which are usually modulated so that the effect changes periodically. The effect sounds similar to the flanger , which achieves certain phase shifts with a time-delayed copy of the original signal.
The effect is created by the audio signal going through two different signal paths. One part of the signal remains unchanged while the other is sent through a series of all-pass filters that shift the sine waves of the audio signal in time in a special way. The shifted signal is mixed back into the original signal, with those waves canceling each other out whose phases are shifted by 180 °. This means that the closer a wave trough approaches a mixed wave crest, the more they cancel each other out, and the quieter the respective frequency component becomes. This results in a comb filter structure ; When using several all-pass filters with shifts of different lengths, a more complex comb filter structure results.
The typical rotation effect is created by modulating the phase shift with a low frequency oscillator .
In contrast to the flanger , which uses tape, bucket chains or digital storage to effect an overall time shift of all sine waves of any frequency , sine waves of different frequencies experience different time shifts in the all-pass filter . In a first-order all-pass filter, for example, the phases of high tones shift very strongly and those of the lower tones shift only weakly or not at all. The resulting comb filter curves are lined up in the frequency spectrum at logarithmic intervals; with the flanger these are distributed linearly. Therefore the sound of the phaser and flanger are not identical.
To set up the all-pass filters, it makes sense to use all-pass filters of the second order, as these produce a phase shift from 0 ° to 360 °, so that when added to the unfiltered signal at the cut-off frequency, a phase shift of 180 ° occurs, which results in the cancellation of this frequency Consequence. With phase shifts of 0 ° or 360 ° the sound is not changed.
The strength of the effect can be regulated by weighting the two signal paths.
The Low Frequency Oscillator is used to make the cancellation frequencies fluctuate periodically. It is controlled by two other parameters, amplitude and frequency.
The American composer Steve Reich discovered the phasing effect for his music in the mid-1960s. Some rock bands of the psychedelic era of the late 1960s used phasing to give their songs a swinging, enraptured sound.
- Electric guitar and vocals in Pictures of matchstick men by Status Quo (1968)
- Choir singing in the chorus of Sheer Heart Attack by Queen (1977)
- Electric bass in Bring on the Night by The Police (1979)
- Electric guitar in Cockoo Cocoon by Genesis (1974)
- Electric guitar in Have a Cigar by Pink Floyd (1975)
- Electric guitar in Strange World by Iron Maiden (1980)
- Drums in Kashmir by Led Zeppelin (1975)
- some synthesizers on the album " Oxygène " by Jean Michel Jarre (1976)
- Hubert Henle: The recording studio manual. Practical introduction to professional recording technology. 5th, completely revised edition. Carstensen, Munich 2001, ISBN 3-910098-19-3 .
- Thomas Görne: Sound engineering. Fachbuchverlag Leipzig in Carl Hanser Verlag, Munich et al. 2006, ISBN 3-446-40198-9 .
- Roland Enders: The home recording manual. 3rd edition, Carstensen Verlag, Munich, 2003, ISBN 3-910098-25-8
- Julius O. Smith: An allpass approach to digital phasing and flanging , Stanford University, Department of Music, Report No. STAN-M-21