Delay

There are two common types of delay found as modules:


 * Analogue BBDs
 * Digital Delays

BBD stands for Bucket Brigade Delay. A bucket brigade or bucket-brigade device is a discrete-time analogue delay line, developed in 1969 by F. Sangster and K. Teer of the Philips Research Labs. It consists of a series of capacitance sections C0 to Cn. The stored analogue signal is moved along the line of capacitors, one step at each clock cycle.

The name derives from a line of people passing buckets of water along the line.

A well-known integrated circuit device around 1980, the Reticon SAD-1024 implemented two 512-stage analog delay lines in a 16-pin DIP. It allowed clock frequencies ranging from 1.5 kHz to more than 1.5 MHz. The SAD-512 was a single delay line version. The TDA1022 similarly offered a 512-stage delay line but with a clock rate range of 5–500 kHz. Other common BBD chips include the MN3005, MN3007 and MN3205, with the primary differences being the available delay time.

By 2009, the guitar effects pedal manufacturer Visual Sounds recommissioned production of the Panasonic-designed MN3102 and MN3207 BBD chip that it offers for sale.

Despite being analog in their representation of individual signal voltage samples, these devices are discrete in the time domain and thus are limited by the Nyquist–Shannon sampling theorem; both the input and output signals are generally low-pass filtered. The input must be low-pass filtered to avoid aliasing effects, while the output is low-pass filtered for reconstruction. (A low-pass is used as an approximation to the Whittaker–Shannon interpolation formula.)