The Delay Effect Explained

There are so many hardware and software-based effects that you might be wondering which ones are actually useful. To help laypersons in the world of music production and mixing make sense of it all, we’ve started a blog series on audio effects. Today, we’re taking a close look at the delay effect.

Delay
How It’s Made
The Tape Recorder
The Bucket Brigade Device
Digital Delay
An Overview of Important Delay-Based Terms
Input
Delay Time
Feedback
Mix/Balance
Filter
Modulation Rate/Depth
High-Pass Filter
Multi-Tap
Stereo
Inversion
Buffer Size
Practical Use
An Alternative to Reverb
A Rhythmic Companion
Widening the Stereo Image
Gear Options

Delay

The delay (or echo) effect is one of the most easily understood effects that you can add to audio. Unlike the reverb effect, which is based on a multitude of echoes, the somewhat similar delay effect keeps things a lot simpler, meaning it’s basically formed by a single echo.

The delay effect isn’t a natural phenomenon, that is, not in the way it’s used in a studio context. Sure, you could stand in between two high-rise apartment buildings, clap your hands and expect to hear an echo effect, but what you’d actually hear is the complexity of reverb, so tens of thousands of sonic reflections with a clearly identifiable, isolated peak. In any case, you won’t end up with a pure delay effect.

How It’s Made

To create an audio-based delay effect, you’ve got three options: tape, BBD and digital. As said, a reverberation room isn’t an option here. MIDI, on the other hand, could work but is based on MIDI signals instead of audio signals, which lands it outside of the scope of this blog.

The Tape Recorder

The basic idea behind the creation of a delay effect is that the recorded audio has to temporarily ‘reside’ somewhere before being picked up again. The size of the place where any to-be-delayed audio momentarily resides essentially refers to the delay-time (see the Buffer Size bit down below for more info). In the early days of delay – we’re talking back in the 1950s – tape was the go-to method for creating delay. A tape recorder would be used to copy the input signal to a running length of tape, which was either tape sold as loops or regular lengths of tape cut and glued together by hand. Tape recorders came fitted with one or more tape-heads, so the process involved reels of recording and reading tape, with the time in between forming the length of the delay. Needless to say, the combination of analogue bits of data and magnetic tape never resulted in crystal-clear sound, but tape-delays sure had (and still have) their charm.

One spin-off of magnetic tape was a rotating magnetic disc called the Binson Echorec: another delay-creating method that involves read-and-write heads. The way the Binson Echorec works can be compared to how hard-drives work. Of its famed users, Pink Floyd is probably the most well-known.

While real tape-echo machines are still being produced today, they’re mostly aimed at filling a niche which explains why they generally don’t come cheap.

The Bucket Brigade Device

Fast-forward to the 1970s and the ‘Bucket Brigade Device’ is now the next big thing. BBDs combine analogue and digital tech. To visualise the concept, imagine a long line of buckets, each filled with an analogue signal, forming a buffer for the recorded sound. The BBD continuously transfers signals from one bucket to the next until there are no buckets left to drop the audio signal in. The last bucket in line is then emptied out and the contents are thrown away, forming the delayed signal.

If this concept rings a bell, it’s because it’s actually based on a ‘brigade’ of people passing buckets of water to put out a fire. That being said, bucket brigade devices obviously don’t come loaded with any actual little buckets.

While the signal is analogue, the ‘brigade of buckets’ is technically a digital sequence in the form of memory (like the RAM inside your computer). As a result, BBD-delays suffer from digital limits in the time-domain. In other words: there’s a limit to the frequency that comprises a sound. A note that stretches beyond that limit is mirrored in pitch, allowing it to return to the audio spectrum in an audibly awkward way. So, to counter any noise, the input signal is first routed through a low-pass filter. The same goes for the output signal.

BBD-based delays are still being used today. Just like tape-echo, it has a unique character a lot of musicians still love. Moog even implemented the technology in some of their effects pedals, including the MF Flange and MF Chorus. The Maestro Discoverer Delay is a more recently-released BBD-style delay.

Digital Delay

Digital delays are super-simple yet super-effective: an input signal is sent to a memory chip and stored there for a short or slightly longer period depending on the set delay-time. There are no moving parts like physical tape-heads, but just like BBD delays, the signal needs to be filtered to get rid of frequencies that are too high.

Digital delays are as clean as delay effects can get, meaning if one form of colouration or another is desired (e.g. tape-echo-style imperfections), it’ll have to be added synthetically.

An Overview of Important Delay-Based Terms

Input

The input marks the place where the audio signal enters. The input usually comes with a level control. In the case of digital and BBD-based delays, a low-pass filter is incorporated to remove unwanted high frequencies.

Delay Time

The delay time determines the duration of the echo. In the world of audio, a couple of seconds is exceptionally long. The average delay time is roughly 0.3 seconds.

Feedback

Feedback refers to the percentage of the output signal that’s re-fed (so added again) to the input. It’s one of the most important parameters since it’s the function responsible for repeating the echos and literally expanding the audio signal.

Mix/Balance

During the creation of a delay, there are two signals: the dry input signal and the wet signal (affected by things like feedback). By tweaking the mix/balance parameter, you can adjust the balance between both signals. In most cases, you’ll want to opt for either a little feedback with loud echos, or a lot of feedback with quieter echos. This has everything to do with the sonic clutter that a loud delay can bring about. Here, dialling in the right balance can be a painstaking task.

Filter

In a way, the filter parameter (also known as low-pass filter, low-shelving or simply LPF) simulates real-life effects like the absorption of high frequencies by walls. During the feedback phase, the audio signal is routed through the filter, resulting in a slightly duller sound. Since the output signal is then fed back in again (and filtered again), the sound only gets duller and duller.

A filter also clearly diffuses the delay effect little by little.

Modulation Rate/Depth

The modulation rate and depth parameters prove there’s technically little difference between delay and chorus effects. They essentially help shape a vibrato effect by affecting the processed (wet) echo signal. The rate parameter, also known as the speed parameter, determines the speed of the vibrato while the depth sets the width. A welcome side-effect of this vibrato is that the echo positions will slightly shift during feed-back, resulting in a certain degree of diffusion. With a lot of delay units, you can turn the delay effect into a chorus effect and vice versa – it’s simply a matter of dialling in the right parameters.

The parameters we’ve looked at so far are the most common parameters for delay effects, whether it’s a tape, BBD or digital delay. Next, we’ll look at a handful of parameters that allow you to take things even further. While the following potential-enhancing functions won’t come loaded into every delay effect out there, they’re certainly worth mentioning.

High-Pass Filter

The high-pass filter (HPF) does the opposite of a low-pass filter, i.e. filter low frequencies out of a feedback loop so that every next echo has a little less bass to it than the previous repeat. A high-pass filter is especially useful when you want to add a massive delay effect to a synthetic bass line. By removing low frequencies, the effect will sound cleaner. When adding delay to the bass, the high frequencies that remain will be enough.

Multi-Tap

During the hey-day of tape-echo, multi-tape-head units already existed and allowed for the creation of multiple echos per cycle. The actual location of these ‘taps’ ensured a certain rhythm and, through feedback, the complexity of the taps only increased.

Nowadays, multi-delays are much more common, especially since the onset of software-based effects. Here, each delay can be given its own delay time, feedback setting and level, resulting in ever more complex echo tails.

Stereo

There’s nothing wrong with widening a delay effect to expand the stereo image. In the case of the multi-tap delays we just discussed, it’s possible to give each delay its own panning position. For example, you can use two delay lines to shape the famous ping pong effect, alternating echos left and right with the same delay time but tweaking the position where one channel is read.

Inversion

Inverting the signal is something that’s often overlooked, even though it’s something that also occurs in real life when sound bounces off the wall and gets inverted by the reflection. Apply inversion to a feedback loop and the same thing happens…again and again and again..

Buffer Size

The last bit of tech-talk before we shift the focus to practical use is about buffer size. The length of the echo is essentially the same as the size of the buffer. In the case of tape, it’s all about the length of the tape; in the case of BBD, it’s about the number of buckets; and in the case of digital delay, it’s about the allocated amount of memory. That said, one thing to bear in mind is the speed at which the tape/BBD buffers/digital reading unit operate.

If the speed is decreased, the delay time increases – much like a vinyl record spinning at a lower RPM. At the same time, the pitch is lowered, which means that delay machines are bound by the maximum number of frequencies they’re able to output.

A tape echo machine is the most straightforward here; the data storage is fully analogue so when the tape reel spins at a slower rate, there’ll be fewer high frequencies in the delayed signal. The same goes for BBD and digital delays, which filter the input signal to remove unwanted highs.

In a nutshell, the size of the buffer determines how much the delay time can be increased (as well as the high frequencies). It basically comes down to quantity versus quality.

Practical Use

Now that we’ve covered the theory behind the delay effect, it’s time to answer the questions: why use delay in the first place? Isn’t reverb a much more natural acoustic effect?

An Alternative to Reverb

Firstly, delay can kind of serve as an alternative to reverb. A natural reverberation comes with a diffused reverb tail at the cost of loudness, since the inverted reflections lower the loudness of non-inverted reflections and vice versa (see the Inversion paragraph above).

To end up with an intense sound, you’d have to seriously up the loudness of a reverb in your mix, probably to the point of overkill. Of course, these days you can also simply set the reverb time to something like twenty seconds, but in the context of music, this is hopelessly impractical. What’s more, reverbs quickly fill up the audio image, so trying to create a reflection here would most likely only result in more fuss. The echo shaped by a delay, on the other hand, can be dropped into the mix at a reasonably high level. It’s just as clear as the input signal, doesn’t really diffuse the sound and doesn’t cram a bunch of reflections into the stereo image. When a vocalist hits a high note in an over-produced pop song, there are few things as effective and pleasing as a delay with the feedback to counter it.

A Rhythmic Companion

This is a musical application that can be so intense it needs to be kept in mind in the early stages of song composition. Say you’ve set the arpeggiator of a synthesizer to a density of eighth notes for synthetic basses. Here, you can fill the empty spaces between the notes with the echoes of those notes by setting the delay time to 3/16th notes (one-and-a-half eighth notes). This kind of effect is especially useful for styles like synth-pop and EDM.

Widening the Stereo Image

If you’re recording a vocalist or guitarist in mono, you end up with a mono recording with little room for any manoeuvre. In this case, you can use two delays to tweak the audio image. Place one delay on the far left and the second on the far right of the stereo image before setting an extremely short (but different) delay time for each delay. You could even add a tiny bit of feedback but don’t push it. You’re now simulating the concept of early reflections in an acoustic room, and filling the entire stereo image.

Sounds good, right? There’s just one catch: it’s not 100% mono-compatible if the effect is too prominently present, so keep a lid on things and remember that no one has ever said mixing is easy. The best solution, by the way, is going for a clean stereo recording using two microphones (preferably a matched pair).

Gear Options

A basic digital delay is surprisingly easy to create. In fact, to code in a modern programming language, you basically wouldn’t need more than a handful of lines of code. As a result, delay effects such as the Behringer VD400 can be kept extremely affordable. Obviously, more memory and computing power does lead to more complex delays like stereo delays, and integrating one or more filters into the signal path also adds more value.

Just how much any given delay effect costs usually depends on the built-in features and options. The Strymon TimeLine delay, for example, boasts a lot more options than the average delay effect. Other cost-deciding factors include the quality of the parts, the type of built-in filter (analogue or digital), the quality of the converters and the total number of units produced (mass-production vs limited-edition models). Thanks to the massive range of available delay/reverb effects, there’s a delay effect for every budget so finding one that works for you shouldn’t be too hard.