what is "Bucket Brigade"?

[lex666]

...sounds like an army armed with buckets.


...All jokes aside, what is "bucket brigade"?

While researching potential new chorus pedals, the MXR Analog Chorus was described as "All-analog bucket-brigade circuitry".

what is it and what are the positives and/or negatives of this type of circuitry?

thx.

Lex

[Andrew Lamprecht]

Re: what is "Bucket Brigade"?

Good question because I have no idea myself.

[the guy who invented fire]

Re: what is "Bucket Brigade"?

Taken from the net because I'm too lazy to write it all out...

This is about delays but analog chorus, flanging, reverb, etc all works the same way form the same BBD's.

Bucket-Brigade delays were the first form of analog audio delay systems to be fully solid-state with no moving parts. Bucket-Brigade Devices (BBD's) are silicon microelectronic integrated circuits that contain hundreds or thousands of capacitive "bucket-brigade" stages. These chips work by taking in the audio on one end, charging a capacitor to "sample and hold" the audio, then a clock pulse shifts this charge from capacitor to capacitor along the chain of BBD stages while charging a fresh sample with each shift. When the audio shifts from one end of the delay to the other the shifting and clocking functions delay the audio. The audio is then recovered in its original analog form at the opposite end of the BBD chain and is then amplified and mixed with the original undelayed signal to create reverb, chorus, and time-frame modulation.

[Chris of Arabia]

Re: what is "Bucket Brigade"?

This >> Bucket-Brigade device

[ratherdashing]

Re: what is "Bucket Brigade"?

Bucket Brigade Device (BBD) is how delay was done before RAM-based digital delay became cheap and small enough to be worthwhile. Prior to BBD the only way to do delay was with magnetic tape or other magnetic storage devices, which were bulky and problematic. Although not perfect, BBD allowed for delay circuits to be much more compact and reliable than tape, which in turn enabled time-based effects to be built into pedals (including delays, choruses, and flangers).

The "bucket" in BBD refers to a capacitor. In the case of a BBD, the capacitor is very tiny (so tiny that thousands of them fit in a single chip) and temporarily holds a very small portion of the audio signal (less than a millisecond). These capacitor "buckets" are arranged in a line (the "brigade") so that the signal can be passed from one to the next. A clock chip regulates how quickly the signal passes down the "brigade" so that by the time it reaches the end it is a time-delayed version of the original signal.

Since capacitors aren't perfect at storing and releasing an audio signal, what you hear at the other end of the BBD chain will not sound exactly like the original. There is usually a loss of treble and clarity as a result of the process, and this "flaw" is part of what makes BBD highly prized by guitarists. BBD doesn't sound like tape delay, but it is a pure analog delay and it does have that nice warmth that works well in many ways.

It's also very difficult to build BBD-based delays with long delay times because of the limited capacity (and cost) of the BBD chip. You need to chain multiple chips together to get more than 300 ms (approximately), which can get pretty costly since BBD chips aren't cheap. Increasing delay time on a digital delay is very easy in comparison, especially nowadays with RAM being so cheap.

BBD has been made technically obsolete by RAM-based digital delay, but it is still kicking around because it sounds so nice. However, if you want perfectly accurate delay repeats, or very long delay times, BBD is not going to work for you.