DDL stands for Digital Delay Line. It is the fundamental technology behind digital delay effects.

Before digital, echoes were created using magnetic tapes (reel-to-reel tape) or analog "bucket brigade" circuits. DDL revolutionized this by converting audio into digital data, temporarily storing it in computer memory (RAM), and playing it back after a set time.

Although the name suggests only "Delay" (echo), a digital delay line is the building block for several other effects:

• Delay/Echo: Long delay times (>100ms).

• Chorus and Flanger: Very short delay times (<20ms) modulated by an oscillator.

• Phaser: Very short delay times.

Therefore, when you see "DDL" in older schematics or manuals refers to the circuit responsible for digitally "holding" the sound before releasing it.