Since the invention of tape-loop echo in the 50's, guitarists have been fascinated with delay effects. These effects can reproduce whole chunks of the original sound at particular time-based intervals, so the detail of the part can be mostly preserved. For this reason, the delay effect has become an essential part of the arsenal of today's guitarist.
A delay circuit memorizes the audio signal and plays it back after a delay time from several milliseconds to several seconds. Most delays will have a feedback control (or regeneration) which takes the output of the delay, and sends it back to the input. If the feedback gain is less than one, the sound will repeat over and over, becoming quieter each time it plays back.
The old delays, like the legendary Watkins Copy Cat were tape machines running a loop of tape that recorded your playing. The sound was replayed through replay heads positioned further around the loop, then erased, ready for the next recording. Varying the mix from different replay heads and/or the speed of the tape, they were able to produce a wide variety of delay effects.
The first compact delay pedals were made with BBD (Bucket Brigade Delay) ICs. Analog delays are less flexible than their digital counterparts and generally have shorter delay times. Several classic models such as the discontinued Boss DM-2 are still sought after for their warm, natural sound.
Modern delays (such as the Boss DD-2) are digital, as memory and digital IC prices have been dropping over the last decade. The digitally encoded signal is less subject to degradation, thus giving a cleaner sound and allowing longer delays.
Common knobs in delay pedals:
The Delay time knob sets the length of delay. This may be called "effect," "range" or simply "delay".
The delay level knob will control the amount of effect that is added to the original "dry" signal.
The feedback knob sets how much delay is fed back to the input. This will control the number of repeats from one to "runaway". This knob may be called on some units "regen" or "repeat".
Other controls can be present like tone, used to cut treble response of the delay so it does not distract too much from the main playing. A neat stereo effect is the ping-pong delay where the repeated sound "bounces" from left to right as it fades out. More sophisticated units offer multiple taps with options to position taps anywhere between left and right output channels for a range of interesting stereo effects.
The DDM-1 Digital Delay Pedal by Arion gives you high quality delay with all the features of the more expensive models at half the price. The DDM-1 delivers a wide range of delays, from very extreme to subtle effects. The pedal has compact and easy-to-use controls for level, feedback, delay time and a mode switch to choose long (120-400ms) or short (60-200ms) delay times.
Weight: 12 ounces
The DigiTech DigiDelay pedal gives you loads of delay time, with up to 4 seconds of delay available. The pedal lets you select various delay types such as stereo ping-pong, tape delay and other custom delay sounds, plus tap tempo so you can set the delay time exactly to the beat. It has two output jacks: Out 1 for mono and Out 2 for stereo operation.
Weight: 3 pounds
The DD-6 Digital Delay is the first Boss delay pedal to offer true stereo delay with panning effects. It comes with great features like built-in tap tempo capability. The delay or hold time is over 5 seconds. A new reverse mode makes it easy to get trippy '60s-style effects, while the newly designed warp mode creates radical delay effects on the fly.
Weight: 4 pounds