A type of delay line which uses an endless loop of magnetic recording tape (or other magnetic media) to produce the delay.  Typically, a loop of tape passes across a record head, where the source material is recorded onto the tape; then as the tape progresses through the mechanism, at some point later it passes a playback head where the recorded signal is reproduced.  Some of the playback signal is then fed back to the record head, mixed with the source material, to produce a repeating echo that diminishes each time it repeats. 

These devices were popular in the 1960s and '70s, when competing all-solid-state technologies were too expensive to be affordable to most musicians.  The two best-known models were the Maestro Echoplex, and the Roland Space Echo.

Antecedents Edit

Tape echo techniques first appeared almost as soon as tape recording began to become popular, right after World War II. When the first tape recorders with separate record and playback heads became available, producers noticed that when the signal from the playback head was monitored during recording, there was a delay between the recorded signal and the played-back signal, and that the delay time was a function of the tape speed and the physical distance between the heads. This was usually considered a nuisance, as it precluded the performer being able to usefully monitor the progress of the recording while performing, but some producers seized on it as a means of producing "slapback" echo (a crude but effective alternative to plate reverb devices or echo chambers, which were too expensive for most small studios).

From here, producers began employing a variety of techniques to produce different length delays. With some tape decks, it was possible to pull out a loop of tape in between the record and playback heads, and wrap it around a microphone stand pole or held pencil, increasing the effective distance between the heads. An unknown producer worked out the original Soundscapes technique using two tape decks placed next to each other. The tape came off of the supply reel of the first deck and was recorded by its record head. It then spanned the gap between the machines and went through the playback head of the second machine, to be then taken up by its take-up reel. This allowed the delay time to be varied by how far apart the machines were placed, and it also had the advantage that after the performance, the take-up reel contained a recording of the proceedings.

Maestro EchoplexEdit

This unit, originally designed in 1959, used an endless loop of tape that was wound in a "whirlpool" cartridge, in which tape entering the cartridge wound onto the outside of the loop and tape exiting the cartridge was pulled from the center.  The endless loop was a key innovation, as compared to the two-tape-decks technique; it allowed the whole package to be much smaller, and the performer never had to stop to rewind a tape. The cartridge was oblong and used a pair of rollers, one at each end.  Back-coated tape was required in order to create the proper amount of slippage for the whirlpool to work. 

The tape transport ran at a constant speed. In order to vary the delay time, the record head was mounted on a carriage that slid back and forth across a rail.  By sliding the head across the rail, the performer could vary the distance between the record and playback heads, and thereby vary the delay time between recording and playback.  A feedback knob controlled how much of the played-back signal fed back to the record head, and by doing so, it controlled the number of times that a recorded sound would be recirculated through the device until it disappeared into the noise floor.

Some Echoplex modes also had a feature called "sound on sound".  When selected, this deactivated the erase function of the record head.  Sound that was recorded on the tape would circulate through the tape cartridge and eventually come back to the record head again, where it would have newly recorded sounds added to it; the built-up sound was then reproduced by the playback head.  These models had foot switches that allowed the performer to turn the record function on and off in order to build up a loop of the desired sounds.  The built-up loop would repeat indefinitely until the sound on sound function was turned off. Although the mechanism was rather primitive, the idea foreshadowed the invention of looper boxes by decades.

Roland Space EchoEdit

The tape mechanism on these units differed from the Echoplex in several ways.  Where the Echoplex had only one playback head, the Space Echo had several.  A front panel switch allowed combinations of the playback heads to be turned on or off in order to produce delays of varying times.  And unlike on the Echoplex, all of the heads were fixed in position; delay time was varied by changing the capstan motor speed.  This had the side effect of varying fidelity as the delay time was changed; the slow tape speeds required for long delay times resulted in loss of higher frequencies because of the self erasure property of tape recording. 

The Space Echo used a unique mechanism for storing the loop of tape.  Instead of winding the tape up on a reel or in a cartridge, the tape after it passed the playback head passed into a flat box area, where the excess tape was allowed to fold itself into a loose serpentine shape.  The serpentine would gradually flow across the storage box until it reached the tape head intake area, at which point the capstan and pinch roller would draw it out of the storage area and across the heads again.  Pressure pads pressing the tape against the heads maintained the proper level of friction so that the loose tape would flow smoothly through the mechanism.

Unlike the Echoplex, some models of the Space Echo were built with other effects incorporated.  Some models contained a spring reverb that could be used in combination with the delay line; some later models contained the noted Roland chorus effect.

Other DevicesEdit

The Binson Echorec worked on the same principle, but instead of tape, it used a wheel with a magnetic surface, something like a modern computer disk drive.

Characteristics of tape delaysEdit

Compared to modern electronic delay lines, the tape delay devices were relatively crude and limited.  Very short delays (those that would be short enough to produce flanging or chorusing) were generally not available because it was not possible to physically place the record and playback heads close enough together.  The sound-on-sound effect on the Echoplexes was of limited usefulness because the only way to change the loop length was to replace the tape cartridge with another one having a different length of tape wound in it.  Some performers kept several cartridges containing tapes of different lengths in order to obtain different loop times.

The tape mechanisms were maintenance intensive.  Like all magnetic tape recording systems, the tape heads and transport mechanisms required periodic cleaning; the tape heads periodically needed to be degaussed, and the tapes wore out (especially on the older Echoplexes where the motor ran continuously, whether the effect was engaged or not) and had to be changed rather frequently.  Occasionally a tape would break at an inconvenient time, and poorly made up splices at the ends of the loop could introduce dropouts or thumps into the output. 

Obtaining a large number of repeats was tricky.  The tape tended to distort and behave non-linearly when pushed hard to obtain more repeats, and careful setting of the feedback control was needed to prevent runaway (although at times, runaway was used as an effect in itself).  It could also cause noise buildup, which tended to mask or drown out newly recorded sounds.

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