Delay - How does it work?

[Techmonkey]

I tried running a search, and I tried searching google too but couldn't really find anything useful.

I've got a pretty good knowledge of electronic engineering, so if anyone wants to give me a technical explanation of how it works that would be awesome. I'm considering building a delay pedal for one of my guitarists birthdays in a few months time, but I'd like to have some idea of how it all works, rather than just doing the electronics-by-numbers follow-the-dots kind of building.

thanks in advance

[superbassman2000]

http://www.harmony-central.com/Effects/Articles/Delay/

tape delays and digital delays are pretty self-explanatory imo, and the analog delays are explained in the link too.

[Techmonkey]

thanks for the link

I'd pretty much figured out that was how they worked, I was thinking more along the lines of how they worked electronically, but in retrospect that seems like a pretty stupid question, again self explanatory.

[bongomania]

There are two main modes: "analog" and digital. The reason I put "analog" in quotes in this instance is that analog delays are in a grey area between the usual definitions of analog and digital.

An analog delay uses "BBD" (bucket brigade delay) chips. The audio signal is stored (in a short burst) in one stage of the chip, then fed into the next stage where it is stored again, then fed into another stage, etc. Each time it is stored there is a gap in the passage of the sound to the output; each time it is released it plays but loses signal strength and fidelity. This results in a repeated pattern of one sound being repeated at diminishing levels with a smearing of the sound.

A digital delay converts the audio to data, and then any number of programs may be written to make a delay happen to that data. The earliest ones were just written to replicate the function of analog delays, but nowadays anything goes.

So you'll want to decide which route you want to take. Note that even if you aren't into learning how to write code for a digital unit, there are pre-made modules/chips you can buy which have the necessary code written onto them already, and all you'd have to do is build it into a pedal with the necessary controls.

Check the usual pedal DIY sites for more details.

[jgsbass]

Sort of like this

[jgsbass]

like this

[jgsbass]

like this

[superbassman2000]

Originally Posted by Techmonkey

thanks for the link

I'd pretty much figured out that was how they worked, I was thinking more along the lines of how they worked electronically, but in retrospect that seems like a pretty stupid question, again self explanatory.

the link did say how delays work electronically

did you read the bottom section?

Implementation

Analog

Perhaps the most common audio recording device is magnetic tape, and this works perfectly well for creating delays. You simply record the incoming signal to the tape, and have a playback head at another point on the tape. The delay is the amount of time it takes the recorded signal to travel from the recording head to the playback head. Delays of this type can be adjusted by changing either the tape speed, or the position of the recording and playback heads. To add feedback to a tape based delay, you can simply send some of the output signal from the playback head to the recording head. Multi-tap delays can be made by using additional playback heads.

There are some interesting features in tape based delays that would be difficult to achieve with digital based delays. If you make the feedback gain greater than one, the signal on the tape will grow. This growth will be limited by the capacity of the tape as it is saturates. This sound may not be desirable for all applications, but you could also conceivably vary the feedback gain over time to shape the sound. If the delay has moveable heads, you could also move the heads while it operates, changing the pitch of the recorded or read sounds.

For very short delay times, analog implementations may actually use circuitry made of up 'sample-and-hold' or 'bucket brigade' devices. The desired delay time can be reached by simply cascading enough of these devices together. Using circuitry like this can provide more precise control over the delay time.

Digital Delay Devices

As memory prices have been dropping over the last decade or so, digitally based delays are now cost effective. The actual operation of digital delays is relatively simple. You have a certain amount of memory available and in each sampling interval, you read a previously stored value from a location in memory (a value of the input signal recorded previously), and then you store the current value of the input signal value into a another memory location (in some cases, this location may be the same location that was just read. This is why a value is read before writing). The next sampling period, you read and write to the next location in memory, and when you reach the end of the memory, you loop around to the first memory location. In signal processing, this is called a circular buffer, and it is quite efficient. When programming delays, you typically manipulate a read pointer and a write pointer keep track of where you need to read from and write to memory. These pointers then increment at each step. Multi-tap delays can be created by simply using some additional read pointers.

[Techmonkey]

Originally Posted by superbassman2000

the link did say how delays work electronically

did you read the bottom section?

*slaps head*

grrr, I r fail at tinterweb. I swear, there's some braincells knocking around somewhere

cheers for the heads up

and thanks for explaining again bongomania =]

looks like this is going to be a fun project