[HN Gopher] The bucket brigade device: An analog shift register
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The bucket brigade device: An analog shift register
Author : LorenDB
Score : 47 points
Date : 2024-11-15 13:27 UTC (2 days ago)
(HTM) web link (10maurycy10.github.io)
(TXT) w3m dump (10maurycy10.github.io)
| brudgers wrote:
| I found Moritz Klein's video on bucket brigade (audio) delays
| informative:
|
| https://youtu.be/4LjP5Y1yxXs?si=l2_dLDy6Cyf6_sGh
| rwmj wrote:
| Burying the lede there! Can someone expand on the bit about how
| CCDs are like bucket brigade delaylines?
| equestria wrote:
| It's basically the same thing, except the initial charges in
| each cell are created through the photoelectric effect when the
| sensor is exposed to light. After that, it's the same conveyor-
| belt-style readout proces as for the BBD.
|
| It's also why CCDs tended to have problem horizontal or
| vertical halos around bright lights. Nowadays, most cameras use
| CMOS sensors, where the amplification and readout circuitry is
| integrated directly into each photosensitive cell.
| Cerium wrote:
| Check out the datasheet for this single row CCD sensor[1]. Look
| at pages 2 and 6, which show the block diagram and control
| signal waveforms. There is a single analog output pin. To read
| the device the "analog shift register" is used, which is a
| bucket brigade device to move the charge from the photo diode
| to the output buffer.
|
| [1] https://www.spectralproducts.com/pdf/ToshibaTCD1304.pdf
| kazinator wrote:
| A bucket brigade delay obtains a sample of a voltage on one
| end, and then shifts copy of that charge among the cells to the
| other end. The delay line as a whole contains a window of
| samples at any point, but that window is such is not accessed.
|
| A CCD line obtains a window of samples directly: the cells are
| charged according to light sensors. Then this window of samples
| is shifted out in the same way as a bucket brigade delay line.
|
| So the main differences are that the bucket brigade is clocked
| continuously, running nonstop and that only one of the cells
| obtains the sample.
|
| The CCD runs only briefly after an image has been exposed and
| capture has been triggered, in order to shift out the samples,
| and sampling takes place at every cell.
|
| A bucket brigade can be slowed down or sped up to change the
| delay. That affects the sampling rate and therefore frequency
| resolution. That's how we can create a chorus effect for
| musical instruments. So the clock speed is a direct functional
| parameter. Slowing down or speeding up the CCD doesn't make a
| difference to the result, except that there's likely an ideal
| range of rates, balancing between the time needed to accurately
| charge one cell to be equal to its neighbor, while being fast
| enough to avoid leakage.
| fecal_henge wrote:
| A modern application of simmilar concept:
|
| https://www.psi.ch/en/drs
| ggeorgovassilis wrote:
| Can someone explain why this doesn't distort the signal? Eg. with
| all these capacitors one might think it would filter out higher
| frequencies?
| duped wrote:
| It does. It also obeys the Shannon-Nyquist sampling theorem
| when you take into account the clock frequency (you can't delay
| signals above half the clock frequency). It also exhibits
| nonlinearities that will create harmonic distortion.
|
| At least in the pro audio space, those qualities are actually
| desirable.
| atoav wrote:
| They _can_ be desirable. If I want to normalize the group
| delay of a bunch of drum mics, I sure as hell not gonna use a
| BBD-Delay for it. But if I want a flavourful analog delay
| onna guitar track, why not.
| pierrec wrote:
| >a nunch ofndrum mkcs
|
| "Am I having a stroke" comes to mind :) A bunch of drum
| mics? I'm no recording engineer, but I guess this is about
| mixing different signals from the same setup, with the
| signals having different delays (possibly due to filters,
| cables, or different types of mics)
| brudgers wrote:
| Distance.
|
| Microphones at different distances receive a signal at
| different times. When combined, the signals are not phase
| aligned. This causes comb filtering where the combined
| waves reinforce and cancel each other.
|
| Though that is sometimes desirable (e.g. comb filtering
| is important for spatial ambience such as reverb).
|
| Some audio engineers find careful microphone placement
| solves many potential problems.
|
| Drums are notoriously hard because modern recording
| techniques use many microphones on a kit.
| atoav wrote:
| Corrected -- smartphone keyboards suck.
|
| Yeah this is about phase alignment of multiple sources.
| brudgers comment explains it quite eloquently.
| brudgers wrote:
| _if I want a flavourful analog delay_
|
| Sounds like use.
| ggeorgovassilis wrote:
| Makes sense, thank you!
| ericwood wrote:
| It's worth noting that in addition to the sample rate, the
| companding to improve SNR and filtering techniques for anti-
| aliasing and reconstruction usually employed to (attempt to)
| retain signal integrity play a large part in the character. A
| lot of people think of them as "dark" but that voicing can
| vary a lot between delays depending on how the designer chose
| to bandwidth limit it; therein lies the real art of analog
| delay!
|
| I've been working on an MN3205 with digital controls and
| pushing it well past its reasonable specs is very fun; 4096
| stages really starts to fall apart past 300ms, and when you
| clock it down to more than a single second you get a wet
| robot fart out of the other end!
| loxias wrote:
| > I've been working on an MN3205 with digital controls...
|
| I should get myself some of those to play with, and you,
| friend, might enjoy a tape delay or two off ebay. (I have
| an Echoplex and it's tons of fun)
| anonymousiam wrote:
| There was also this popular (in the day) successor (sad-1024 dual
| analog delay line)
|
| https://www.alldatasheet.com/datasheet-pdf/pdf/1161976/ETC2/...
| Eduard wrote:
| do I interpret the screenshots correctly: that's a whopping 2.5
| millisecond delay?
| alfiedotwtf wrote:
| Which is within the range needed for things like guitar pedals
| (flangers and chorus)
| amelius wrote:
| If you momentarily put two capacitors in parallel, the charge
| will divide between the two, right? So how does all the charge
| end up on the other side?
| rcxdude wrote:
| The other side of the 'input' capacitor is pulled down to a
| much lower voltage, which means the charge prefers to flow into
| it. (And then this alternates so the next time the one it is
| transferring charge to is pulled lower)
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