Electronics > Beginners
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.
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