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About BBDs
I am often asked what gives analog delays their characteristic sound. The
answers I usually see given are not what make them sound different to me.
A BBD (Bucket Brigade Delay) works by storing a momentary snapshot
“sample” or charge in a capacitor isolated by a FET network. It passes this
sample from one capacitor to the next via a bi-phase clock until it reaches
the output. These capacitors are like water in a bucket brigade line, passing
the audio sample from one “bucket” to the other until it reaches the “fire”
at the end. BBDs were originally designed for use in radar to determine the
distance to objects. By sending out radar signals, and delaying it through a
BBD one can adjust the delay time compared to the reflection. When the
reflection phase cancels out the delayed sample you have 1/4 the delay
time/distance. Early digital oscilloscopes, like the Tektronix 2440, also
used them as temporary storage since Analog to Digital converters of the
time were too slow. Digital cameras still do this today for the same reason.
Now they are used for audio in delays, chorus and flangers.
The ADG-1 uses a recreation of the Matsushita/Panasonic MN3005 PMOS
BBD from Xvive™. The MN30xx series BBDs use a higher voltage for
more clarity, lower noise, more headroom and lower distortion than the
MN320x NMOS types usually found in most stomp boxes, however they
have lower range of delay time (cannot clock as fast) compared to MN320x
BBDs. These BBDs sound very close to the Panasonic parts but are more
transparent, less animated with less character and appear to have a lower
noise floor. In addition, the clock speed does not change the sound as much
as their predecessors did.
Perhaps the biggest reason BBDs can do what digital often cannot is due to
Fractional Delay, often referenced as the Doppler Effect. Since the clock
moves continuously, the delay time has every single continuous increment
between each step. That is why analog delays make great dive bombing
sounds. The ear is very sensitive to this and perceives this as distance and
movement. This trick is how movies pan sound or make you think a bullet
just whizzed over your head. Most digital delays simply cannot do this.
