<4>
With a fixed clock frequency, they can only take a sample step every 48 or
96KHz and step at that increment. This only simulates fractional delay and
is not true fractional delay. The ear can perceive this difference and so it
does not feel correct to the brain. Note early digital delays like the Lexicon
PCM 41/42 did use a variable clock using a different, now obsolete,
process, but these are the exception not the rule. Most hybrid analog delays
that use a MPU digital clock do not use steps small enough for true
fractional delay, so while they may use a BBD the modulation does not
sound as natural as some picosecond step clocks or true analog modulation.
In addition, BBDs have some other “artifacts” that give them their unique
sound. The transfer characteristics, noise, distortion and frequency
response vary depending on the bias voltage and clock frequency making
the sound change as the delay time changes. They also do not put out the
entire signal at the same time. Half the signal is a ½ clock behind the rest
of the signal, yet combined at the same time, making for a strange smeared
time domain merger and mixing of the signals slightly out of time.
Other components also affect the sound. The design of the companding and
emphasis/de-emphasis network, designed to improve the signal to noise
ratio, affects the animation, breathing, overshoot and tightness of the sound
like a compressor with a slow attack and fast release. The design of the
filters affects the frequency response, peaking or ringing, and potential
aliasing or ring modulation. There are many more parts of the analog
design often overlooked in digital recreations that affect the sound as well
including the clipping, feedback network, clock stability modulation wave
shaping/curves (exponential or linear, etc.) that are all important to get that
great analog delay sound.
For more reading about BBDs check out these great websites:
https://www.electrosmash.com/mn3007-bucket-brigade-devices
https://www.premierguitar.com/articles/25035-behind-the-bucket-brigade
https://pedals.thedelimagazine.com/bbd-chips-the-magic-behind-analog-
delay-pedals/
