Analog Delay

[IvoS]

Just a general question on how is the analog delay topology executed. I have an idea of how the signal in digital domain can travel, something like: ADC-processor-memory-DAC or something like that. But how they really do it in analog delays for a musical instrument for example.

[Yansi]

You seem to not have googled hard enough, so a few hints:

Small delays (couple us): Run a length of wire (coaxial).

Small delays (couple tens of us): Use accoustic wave delay line (the typical TV set 64us delay line for decoding PAL)

Small delays for low and audio frequency signal: allpass filters (just a fraction of signal period)

Anything above that needs a kind of memory array. There are various type of such memory, including magnetic tape,  mechanical (spring reverbs), up to the signal sampling ones.

These sample based ones can be of two types: Analog and digital. Search for bucket brigade delay line. It is sort of an analog DRAM. It is how CCD's are read image data from.

THe digital being the obvious one: ADC, memory, DAC.

[T3sl4co1l]

Yup.  Here's an impressive, but somewhat less portable example, the plate reverb:



It's noteworthy that springs are dispersive, so you can't expect to send a pulse in and get it out the other end without it turning into a bunch of ripples.  This is perfectly fine for a spring reverb (a somewhat random echo is probably more realistic, anyway?), but not so desirable for signal processing purposes!

As for purely electronic and analog, yeah, it's dreadfully difficult to do that over any meaningful bandwidth and duration.  Electronic signals easily move on the scale of nanoseconds; to get even millisecond delays is practically heroic effort.  Mechanical or digital solutions are by far the better approach.

Tim

[Benta]

In earlier days, ICs called a "bucket brigade" were available for analog delays.

[mikerj]

I can remember taking apart old colour TVs in my youth and being confused by the strangely rippled blocks of glass with wires coming out.  These were piezo driven acoustic delay lines to hold a line of colour signal which required 64us; quite a decent delay for a relatively small component.

Also don't forget the mercury delay line, which was used as memory storage in very early computers.

[Zero999]

In earlier days, ICs called a "bucket brigade" were available for analog delays.

Yes, I remember reading about BBDs in the Maplin magazines in the early 90s. They were quasi-analogue as they still involved sampling the signal and the bandwidth was very limited by the technology of the day.You had a choice between a low bandwidth and long delay or higher bandwidth and shorter delay.

[Gregg]

Relay logic was considered the reliable means of controlling many things 40 years ago.  Time delay and interval relays with many configurations were available.  Here is a picture of the control panel of a 3000 amp 480V 3ph Zenith transfer switch manufactured in the early 80’s.  The problem with this device is that the time can’t be reset once the relay is energized without damage to the relay (blue caution label on the right spells this out). Note the black relays for voltage and phase sense.

[Zero999]

Relay logic was considered the reliable means of controlling many things 40 years ago.  Time delay and interval relays with many configurations were available.  Here is a picture of the control panel of a 3000 amp 480V 3ph Zenith transfer switch manufactured in the early 80’s.  The problem with this device is that the time can’t be reset once the relay is energized without damage to the relay (blue caution label on the right spells this out). Note the black relays for voltage and phase sense.

I think you're confused. That's not what the original poster is talking about. They're talking about delaying a signal, i.e. time shifting it, not delaying an event with a timer relay.

[IvoS]

Yup.  Here's an impressive, but somewhat less portable example, the plate reverb:



It's noteworthy that springs are dispersive, so you can't expect to send a pulse in and get it out the other end without it turning into a bunch of ripples.  This is perfectly fine for a spring reverb (a somewhat random echo is probably more realistic, anyway?), but not so desirable for signal processing purposes!

As for purely electronic and analog, yeah, it's dreadfully difficult to do that over any meaningful bandwidth and duration.  Electronic signals easily move on the scale of nanoseconds; to get even millisecond delays is practically heroic effort.  Mechanical or digital solutions are by far the better approach.

Tim

WOW. 

[David Hess]

...

Small delays for low and audio frequency signal: allpass filters (just a fraction of signal period)

Anything above that needs a kind of memory array. There are various type of such memory, including magnetic tape,  mechanical (spring reverbs), up to the signal sampling ones.

Mechanical transmission lines using springs with transducers at each end also work as audio delay lines.

It's noteworthy that springs are dispersive, so you can't expect to send a pulse in and get it out the other end without it turning into a bunch of ripples.  This is perfectly fine for a spring reverb (a somewhat random echo is probably more realistic, anyway?), but not so desirable for signal processing purposes!

That is true of all transmission lines to a greater or lesser extent.  With proper design, dispersion can be made insignificant below a selected frequency.

[Yansi]

...

Small delays for low and audio frequency signal: allpass filters (just a fraction of signal period)

Anything above that needs a kind of memory array. There are various type of such memory, including magnetic tape,  mechanical (spring reverbs), up to the signal sampling ones.

Mechanical transmission lines using springs with transducers at each end also work as audio delay lines.

[T3sl4co1l]

Funny, I skimmed over that initially, too.  Then I re-read the post and realized it was included.  Go figure!

Tim

[Yansi]

At least I have learned that also plate reverbs exist. I've never heard of them round here in the dark corners of the former iron curtain.

[TimFox]

With respect to analog delay lines:  I remember a feature in Electronic Design, sometime around 1990?, where Plessey had made a fast-sampling bucket-brigade device to allow rapid signal capture before feeding the samples into a slower ADC for DSO application.  The bucket-brigade was quite long, and didn't fit into a roughly square form factor on the chip, so it was spread out as a Z shape, with wasted space inside the Z.  The designer had inserted a small steam locomotive shape (from his kid's coloring book) into the gap, since the line looked much like rails separated by ties (sleepers).  Tektronix was famous for illuminating their schematics, but this is the only such artistic effect of which I am aware in a monolithic device.

[chemelec]

I have a 15 inch long Spring Delay.
Been laying on my shelf for over 15 years, and I have never used it.
Consists of 3 parallel Springs with Send and Receive coils.
Soon to go into the Garbage Can.

[David Hess]

Mechanical transmission lines using springs with transducers at each end also work as audio delay lines.

I mean the mechanical transmission line is literally a spring.  A spring is the mechanical equivalent of a transmission line loaded with a high dielectric constant for a very low velocity factor.

They were commonly used for audio reverberation effects.

[Yansi]

But I have already mentioned spring reverbs. Why I was quoted in #9 then?

[richard.cs]

With respect to analog delay lines:  I remember a feature in Electronic Design, sometime around 1990?, where Plessey had made a fast-sampling bucket-brigade device to allow rapid signal capture before feeding the samples into a slower ADC for DSO application.  The bucket-brigade was quite long, and didn't fit into a roughly square form factor on the chip, so it was spread out as a Z shape, with wasted space inside the Z.  The designer had inserted a small steam locomotive shape (from his kid's coloring book) into the gap, since the line looked much like rails separated by ties (sleepers).  Tektronix was famous for illuminating their schematics, but this is the only such artistic effect of which I am aware in a monolithic device.

I remember hearing about that when I was working at a former Plessy site, several owners later but with many of the original staff. Apparently it came up in a court case where someone had copied the masks but claimed that the design was obvious and they'd come up with it independently.

[Gyro]

Just looking on ZeptoBars. They have recently posted die shots of the MN3102 Bucket Brigade clock driver chip and the MN3207 1024 stage Bucket Brigade analogue delay line. Nice photos...

https://zeptobars.com/en/

[Bassman59]

Just a general question on how is the analog delay topology executed. I have an idea of how the signal in digital domain can travel, something like: ADC-processor-memory-DAC or something like that. But how they really do it in analog delays for a musical instrument for example.

The Bucket-Brigade Device was the most common way to get specific delay times for audio use. They work in much the same way as the Charge-Coupled Device (CCD) works for imaging, except instead of the input to the delay being a pixel voltage, it's a signal voltage fed in.

The BBD is an apt name because that's basically how it works. You have a string of charge "buckets" all in series. The input signal is "clocked" into the first bucket, and then on each clock, all of the charges in each of the buckets is transferred to the next bucket in the string. At the end of the line, the output of the last bucket is low-pass filtered and buffered to drive the delay line output. It is sampling, since on a regular basis a snapshot of the input signal is captured and dumped into that first bucket. But it is not quantization, as the signal in the buckets is never converted to a digital number. It remains just a voltage (a charge on a capacitor) through the entire delay line.

Delay time is set by two mechanisms, which are used together. One is simply the number of "buckets" in the string. More buckets, more delay. The second is the clock rate. Faster clocking means shorter delay time. The clock rate is the sample rate, so the lower the clock rate, the lower the bandwidth of the system. The upper limit to clock frequency is set by the clock drivers. Each bucket is connected to the previous and the next by FET switches, and the clock controls the gate of each, they're all connected in parallel. Thus the clock has to be able to drive the capacitance of hundreds of gates in parallel.

[RandallMcRee]

Traditional analog delay

https://www.uaudio.com/blog/allpass-filters/