Mixing : Delays - Part 2

You need to learn how each delay time feels and what feelings or emotions each delay time evokes. Then, when you hear a song that has a similar feeling or emotion you will know which delay time might work.

Different delay Times

Let's define specific delay time ranges so that you can get to know them and incorporate them into your memory time banks.

More than 100ms

Professional engineers refer to this length of delay as echo. However the real world (and my mom) use the term echo to refer to reverb. For our purposes, we will use echo to refer to a delay time greater than 100ms, not reverb.

When setting a delay time greater than 100ms, it is important that the delay time fits the tempo of the song, otherwise it will throw off the timing of the song. The delay time should be in time, a multiple of, or an exact fraction of the tempo. If you know the beats per minute of the song, the following chart gives the relationship between tempos and delay times.

                               Beats Per Minute                   Time Between Beats

                               60   bpm                                1000    ms

                               90   bpm                                 666.6  ms

                              120  bpm                                 500     ms

                              150  bpm                                 400     ms

                              180  bpm                                 333.3  ms

                              210  bpm                                 285.7  ms

                              240  bpm                                 250     ms

Tip: / If you know the tempo of the song, you can figure out the delay time with the following formula:

Delay time = 60,000 / beats per minute.

Then any fraction or multiple of that delay time will also fit the tempo of the song. For example if the tempo is 100 BPM then the 600 ms would fit the tempo. But 150 ms, 300 ms, and 1200ms would also fit.

If you don't know the beats per minute (bpm) of the song, use the snare drum (or some other instrument playing on a continuous patterns) to set the delay time. Even if you are going to put the delay on the vocals, for example, put the delay on the snare to set the delay time to the tempo.Again,once you have found a delay time that works, any multiple or fraction of that time might also work.

A delay time over 100ms creates a dreamy effect and is most commonly placed in songs with slower tempos where there is room for the additional sound. Therefore, the more instruments and the more notes in a mix, the less often this delay time is used. This is pretty obvious - if you have no room in the mix don't add more sounds. This is especially true when there is feedback on a long delay time. The delays take up so much space in a mix that they are often only turned up at the ends of a line, where there is enough space to hear echoes by themselves.

Tip:  / Feedback is created by feeding back the delayed signal into the input, so the sound repeats, repeats, repeats.

60 to 100 ms

You can hear this delay time, commonly referred to as slap, on the vocals of Elvis Presley and in rockabilly music. In fact, there is about an 80ms delay between the syllables "rock" and "a" in the word "rockabilly."

This effect can be quite helpful in making a thin or irritating sound (especially for a voice) sound fuller. It can help obscure bad vocal technique or pitch problems. In fact, a slap can be used to bury any bad sound. However, you never want to bury anything to deep. Add too much delay on a bad vocal and not only do you have a bad vocal, but you also have a bd mix. On the other hand a sea can make a vocal seem less personal. If you have an incredible singer, you might forego using any delays. Just put it out there with a little reverb and let it shine.

30 to 60ms

Put your lips together and blow a raspberry, this sound technically called a "motorboat." The time between each flap on your lips is approximately 50ms. Delay time in this range is referred to as "doubling" because it makes a sound seem like it was played twice, or doubletracked. When a part is sung or played twice, there will naturally be a time delay ranging from 30 to 60ms (no one can ever sing or play a part twice exactly in this time). Therefore adding a delay of this length makes it sound like the part has been played twice. The beatles used this effect extensively to simulate more vocals and more instruments.

Just like a slap, doubling helps to obscure a bad sound or bad performance. So it can be used to help bury things in the mix.

Likewise, since it does obscure the purity and clarity of a sound, you should use it selectively, depending on the sound, song and style of music.

Tip: / Although doubling makes a sound seem like it has been played twice, it is a different sound than if you actually doubletrack a sound. In fact doubling often sounds so precise that it sounds somewhat electronic. This is especially true on vocals and simple sounds. However, if a sound is complex, especially if the sound is a combination of sounds (like a bunch of background vocals or a guitar sound with multiple pics), then you don't notice the precision of the delay. Therefore when you put doubling on 20 vocals, it sounds like 50 vocals and it sounds incredibly natural.

1 to 30ms

An unusual thing happens with this type of delay, commonly known as fattening. At the delay time, our brain and ears are not quick enough to hear two sounds; we only hear one fatter sound.

The threshold between hearing one sound or two sounds actually varies depending on the duration of the sound being delayed. Also the farther the sounds are panned separately, left and right the shorter the delay time before you hear two sounds. For example a guitar panned to the center with a delay in the center might require at least 40 milliseconds to hear two sounds; whereas, if the guitar and delay are panned left and right, you might hear two sounds beginning around 20 milliseconds. The following chart gives approximate thresholds for some instruments with different durations (actual thresholds will depend on the particular timbre and playing style of the instrument):

                        Approximate thresholds between hearing one sound versus two

                                                      Hi - hat                  10ms

                                                      Percussion             10ms

                                                      Snare                      15ms

                                                      Kick Drums           15ms

                                                      Piano                      20ms

                                                      Horns                     20ms

                                                      Vocals                    30ms

                                                      Guitars                   30ms

                                                      Bass Guitars          40ms

                                                      Tubas                     40ms 

Besides reverb, fattening is the most-used effect in the studio, mostly because it doesn't sound much like an effect. Fattening is the primary effect used to make a sound stereo, which has a certain magic to it. When you put the original "dry" instrument sound in one speaker and put a delay less than 30ms in the other speaker, it "stretches" the sound in stereo between the speakers.

Fattening can make an already beautiful acoustic guitar or piano sound incredible. Fattening is very effective in making a thin or irritating sound fatter and fuller. It also appears to make a sound more present simply because when a sound is in stereo, it takes up more space between the speakers. This is especially effective when you want to turn a sound down in the mix but still have it be discernible.

You have to be careful with fattening, though, because it uses up your space between the speakers. Fattening will make a mix fuller and denser, so you must make sure there is enough room between the speakers. Therefore, fattening is used most often when there are fewer notes and sounds in the mix. On the other hand if you want to create a wall of sound, even if the mix is already busy you can add fattening to make it more busy. (This blow's people's minds.) This is commonly done in heavy metal, alternative rock and some new age music.

0 to 1ms

This soft of a delay time causes phase cancellation. I will address only the critical aspects of phase cancellation here. But keep in mind that phase cancellation is a very serious problem in recording and I highly recommend that you do further research to gain a complete and clear explanation of the problem it causes.

Phase cancellation happens when two of the exact same sound, like those created with two mins or two speakers, are a little bit out of time. One example is when you switch the positive and negative wires on one of the two speakers. Now, one speaker is pushing out while the other is pulling in. When a speaker pushes out, it creates denser air than normal. When a speakers pulls in, it creates more spaced out air than normal (rarefied air). When the denser air from one speaker meets the spaced-out air from the other speaker, you end up with normal air, normal air equals silence. This means you could have two speakers blasting away and theoretically you could hear nothing.

There are many companies now using phase cancellation to quite the world. This technology is used in automobiles, on free-ways (instead of cement walls on the sides of the freeways), in factories, and even in headphones to cancel out sounds around you. Marriage counselors are selling them by the dozens.

If you have two mins on one sound at two different distances, one mic might be picking up denser air while the other mic is picking up spaced-out air. Put the two mins together in the mix and they will tend to cancel each other out, though not completely. 

Phase cancellation degrades the sound quality in the following ways.

• Loss of volume. You lose volume when both miss are on, especially when you're in mono (which, by the way, is one of the best ways to detect phase cancellation - put the board in mono or pan both sounds to the center).
• Loss of Bass. You lose bass frequencies, making the sounds thin.
• Loss of image. Most importantly, you lose the clarity and precision of the perceived image of the sound between the speakers. The sound seems to be more "spacey." Though some people like this effect, most people are addicted to clarity these days. If the mix is even played back in mono (as on TV or AM radio), the sound will disappear completely.

There are many ways to curb phase cancellation. The primary way is to simply move one of the pics. If both miss are picking up the sound in the same excursion of the wave, there will be no phase cancellation.

2 Mics picking the sound in phase

It takes 1ms for a complete wave of 1000Hz to pass by us. If you were to set a delay time of 0.5 on a sound, it would put it out of phase. Therefore, you can use a digital delay to put the sound back in time.

Finally you can remove a large amount of phase cancellation through isolation. Often, the bleed of a sound into a second mic will cause phase cancellation with the first mic. By using baffles or noise gates, you can reduce the bleed in the second mic, voiding the phase cancellation. 

You can read more about the most important things you need to know about mixing, and how to setup the compressors properly depending on the task you want to realize in Dave Gibson's book "The Art of Mixing 2nd Edition" A visual guide to recording engineer and production.