Echo, more commonly referred to as delay, is a very common effect used in sound editing. In fact, it is one of the oldest special effects in existence. An echo works by repeating a specific sound multiple times, thereby delaying the time of the repeated sounds. The echo sound is produced because the original sound has been stored electronically in the recording medium and then played back.

Types of Echo
There are a few different ways to use echo. The repeated sound can simply be repeated over and over, or it can be put directly back into the original recording. More than one type of echo exists. Phasing is a very short type of echo, while mid-level ones are called flanging. Long echo is called chorusing. A specific type of echo called slapback delay is used in conjunction with reverb. Slapback delay is a very fast playback of a single signal. Audio reinforcement is an especially short type of phasing. 
 
Digital and Analog Echo    
A marked difference exists between digital and analog echo, particularly in the quality of the effect. While digital echoes can make flawless copies of the original sound, analog echoes have a more natural effect due to a poorer response time. As a result of the perfect mimicry of digital echo, there tends to be more problems with getting it to work properly. While digital editing has improved many areas of sound, analog remains superior when creating echo. Getting digital echo to sound natural requires much more effort than simply producing analog echo.    
 
Echo and Timing   
There are several possible problems inherent in using echo. One of the most obvious is that an echo may not fit with the original tempo of the initial sound; an echo that does not match the tempo will create an unpleasant listening experience. This problem can be solved by calculating the amount of time needed so that an echo will fall on a specific beat. However, this does not fix the problem entirely, because the echo may still clash with the tone of the note on which it falls.

Mulittap Echo
Another way to remedy the issue of mismatched tempos is to create multitap echoes. Multitap echoes do not require that you match the echo up perfectly to the original speed of the sound, because they are far more complex. To create a multitap echo, time various delays so that they are not exact multiples of each other. This creates a great deal of variation and, as a result, a very interesting effect. After the timing has been set, feed the delays into an input device again. The result is that the complexity of the echoes will increase even further, even though the sound is decaying. While this effect can resemble reverberation, the two should not be confused. Another term for multitap echoes is “Echoplex.”

Ducking Delay and Reverb    
Another problem related to echo is that it can often sound messy due the fact that the sound is reflecting off of multiple objects in the area. To produce a cleaner sound, it is often helpful to add a small amount of reverb to the echo. In addition, echo can make the sound as a whole sound cluttered. To avoid this problem, use a technique called a ducking delay. This type of delay drops the sound level when it receives a strong signal; it rises again during quiet sections. You will need extra tools to do this: either a compressor or a gate that is set in ducking mode. Then feed the delay unit through the ducker, which triggers it from the signal. Of course, you can bypass the extra tools if ducking delay is already included with your sound editing package.