Delay is defined as the splitting of a signal into separate components, the slowing of one of these split signals, and its subsequent re-introduction into the original signal.
Echo is defined as a delay of approximately 35 ms. in which the regenerations are evenly spaced and in which the release portion of the sound envelope is even as well. This is also sometimes referred to as Early Reflections.
Reverb is defined as a delay less that 35 ms. in which the regenerations are randomly dispersed and in which the release portion of the sound envelope is random as well. This is also sometimes referred to as Later Reflections.
abit of history .... children
Before the invention of magnetic recording, the first delay was used in radio broadcasting. It was created by sending the audio signal across telephone lines to a city hundreds of miles away and then bringing it back. The time it took for the signal to travel the distance across the phone lines caused the signal to be delayed somewhat in comparison to the source signal.
After magnetic recording had been introduced, Les Paul realized that the space between the record and playback heads of a tape recorder could be used to create a Tape Delay. Later, to increase the delay time, he tied two tape recorders together and, with the advent of variable speed playback decks, he could control the actual delay time by slowing or speeding up the second deck. But Les Paul was faced with a dilemma every time the tape on the second deck ended. The answer came a few years later with a new form of tape delay (new back then) called Echoplexing. This utilized a continuous tape loop which allowed for continuous delay without running out of tape. Echoplexers were used up into the seventies and may still be found in some studios today (usually on a dusty back shelf though).
The mid seventies brought the beginning of the digital age, and with it, the first digital delay lines or DDL's. However, due to the cost of digital technology back then, DDL's generally only had about a 10 - 15 kHz bandwidth. Its primary use was to keep the signal in particularly large venues in sync between the front and back of house speakers.
In the late seventies, Analog Delay became popular because of its reduced price. Many musicians still claim that the analog delays were much fatter and warmer sounding than digital delays, however anyone who has used one knows they are subject to extraneous noise from EMF and other sources.
Echo and Reverb, in pre-digital days (was there really such a time) was created by playing an audio signal in a room with very hard surfaces and recording the reflections. These type of rooms, known as Live Rooms, offered engineers a chance to control the parameters of the reverb simply by changing placement of the microphone capturing the reflections. If you needed more reverb, you simply moved the mic further from the sound source, less reverb was achieved by moving the mic closer to the sound source. Extravagant ways of changing the envelope of the reverb were soon devised, such as hanging sound absorbing mats on some walls, the use of moveable baffles, etc.
Today, engineers for the most part record signals dry (without any effect) trying to get the best quality of signal, and then add these types of effects when making the final mix of a recording. This has led to a definite change in the structure of recording studios. Where once only the very rich could afford rooms that offered high quality reverberation, now anyone with a relatively quiet recording area can manipulate sounds after the fact with high quality digital processing. Digital processing has become so standard in fact that many home stereos offer some type of reverb for mic inputs.
