Delay effects have retained their status as key tools for electronic musicians for more than 50 years. Although most modern delay units use digital technology to generate their effect, many musicians still turn to older technology to achieve the warmth and character associated with earlier hardware units. One such example is a bucket-brigade delay, which was widely used in many different genres throughout the 1970s and 1980s. In this feature, we explore how a bucket-brigade delay’s structure leads to its unique sound and delve into some of the creative possibilities that bucket-brigade delays present electronic musicians.
AN INTRODUCTION TO BUCKET-BRIGADE DELAYS
The central idea of a bucket-brigade delay dates back to 1969, when Philips engineers Sangster and Teer noted that a delay effect could be achieved by sending a signal through a chain of capacitors. In this chain, the first capacitor briefly retains an incoming signal, then passes it on to the second capacitor, which briefly retains the signal, then passes it on to the third capacitor, and so on. The bucket-brigade delay gets its name from this configuration, which looks like a line of firefighters passing buckets of water.
When the signal emerges from the final capacitor, it has been delayed by the amount of time that it took to pass through the chain. The length of this delay time is controlled by the rate at which each capacitor passes its charge to its neighbor—the higher the rate, the shorter the total delay time.
Fig. 1. A typical signal path for a bucket-brigade delay Because each capacitor in a bucket-brigade delay only passes its signal along the chain at discrete times, any high-frequency components of an input signal that enter this chain could create an inharmonic distortion known as aliasing. To combat this, bucket-brigade delays also contain a pair of lowpass filters—one each side of the delay line—that remove any high-frequency components from the signal. In addition, many bucket-brigade delays also compress an incoming signal before feeding it into the first lowpass filter, then expand it after it emerges from the second lowpass filter, to prevent overloading of the capacitors and to reduce unwanted noise. This signal path (see Figure 1) gives bucket-brigade delay units their unique sound. As with many other delay effects, the output signal can also be fed back to the start of the signal path, to repeat the whole process.
Bucket-brigade delay units offer many opportunities to get creative with delay effects. Thanks to their lowpass filters, sounds often emerge with hollow, ethereal characteristics. When used with long delay times, bucket-brigade delays can create haunting, distant echoes of entire musical phrases. With shorter delay times, bucket-brigade delays can add rich textures to sounds and help to achieve the impression of a heavily filtered, unison performance.
Another creative use of bucket-brigade delays is to change the rate at which a signal is passed along the delay line when the buckets are already full (i.e., when a signal is already passing through). This creates a sweeping, melodic, bubbling effect that has been widely used in many musical styles. By modulating this change (e.g., via an LFO), a bucket-brigade delay can also create a pulsating sound for chorus and vibrato effects.
Fig. 2. The EHX Deluxe Memory Man bucket-brigade delay HARDWARE AND SOFTWARE BUCKET-BRIGADE DELAYS
A wide range of hardware bucket-brigade delay units are available on the market. Figure 2 shows a classic hardware bucket-brigade delay unit called the Deluxe Memory Man. As with many types of hardware, some bucket-brigade delay units sell for huge amounts of money because many musicians seek to capture a specific signature sound in their work.
Thanks to analog modeling techniques, a range of digital plug-ins that mimic the core functionality of hardware bucket-brigade delays are now also available. Instead of passing a physical charge through a chain of capacitors, digital bucket-brigade delay units pass a signal through a memory buffer. Most digital bucket-brigade delays use the same signal path as shown in Figure 1. As with the hardware units, the lowpass filters ensure that the discretetime sampling of the input signal does not produce audio aliasing. Although the compressor and expander are not necessary to tackle the physical issues associated with passing charge through a series of capacitors, most digital bucket-brigade delays still implement these features in order to reproduce the characteristic sound of their hardware cousins.
Digital bucket-brigade delays also offer a wide range of benefits associated with digital music production, which open doors for many creative possibilities. For example, by using host automation it is possible to program far more complex parameter changes than is feasible to perform by hand. Also, it is possible to synchronize a digital bucket-brigade delay to the master tempo of a track. This feature is very helpful for creating delay effects with large amounts of feedback, because it ensures that the repeated echoes of each sound always align with the beat.
Fig. 3. The Bucket-Brigade delay unit in Future Audio Workshop’s Circle2 Synthesizer Figure 3 shows the bucket-brigade delay module in the Future Audio Workshop’s Circle2 synthesizer. This synthesizer has a semi-modular setup that enables parameter modulations via the small circles on the interface.
By modulating the delay time and feedback parameters, digital bucket-brigade delays produce complex, evolving effects that can add character and variation to any element of a track. Thanks to the warmth and character of such effects, bucket-brigade delays are the ideal go-to solution for creating delays that are bursting with personality.
A demo of Circle2 is available as a free download from the Future Audio Workshop website and offers an excellent opportunity to gain handson experience of working with a bucket-brigade delay. You can hear audio clips demonstrating bucket-brigade delay effects at emusician.com.