Using two turntables to create echo effects requires that the records being used must be identical. Next the turntables themselves should be matched for speed. Most DJ turntables have strobes to ensure that the platters spin at the correct speed. Set both turntables to the same platter speed and use the strobes to match speed precisely. Line up each record to the same spot using cuing and backspin on the platters.
Simply stated, echo is a time-delay effect. In a dual-turntable setup, the second record serves as echo signal, an exact repeat of the original sound. The DJ controls how and when this signal occurs by manipulating the platter of the second turntable, releasing it in a controlled way and raising its fade control when the echo effect is desired. This creates a simple "slap" echo with one repeat. How the repeat is used determines the final sound.
Ambient echo can give the sound of a live concert to a song. In this case, the second record is delayed a tiny amount, usually 60 to 100 milliseconds, often by simply backing up the platter a small amount. The mixer is used to set the volume of the echo signal so that it doesn't overwhelm the original signal. If the mixer is equipped with equalization, adjustments can be made to further reduce the sonic clutter of the echo.
Musical echo is a time delay based on a musical interval set by the song. The second platter is delayed in time with the beat of the song. Typical intervals are quarter and eighth notes, the "one" and "and", when counting "one and two and three and four" in time with the song. The mixer may be used in sync, also to allow only chosen echoed phrases to reinforce the main song.