Article 7

Bobby Nathan's

Keyboard Magazine "In The Studio"

Article # 7

USING PRE-DELAY AND REVERB

By Bobby Nathan

For those of of you that read last months article on echo and delay, this is a continuation on the use of ambience.

As I promised here is my definition of pre-delay. Pre-delay is essential to natural ambience. Pre-delay is a is the amount of delay before the reverb chamber. Pre-delay follows all the rules that govern synthesizing natural echo whether using a tape or digital delay unit. When using a delay unit for pre-delay, the direct signal is not sent to the reverb chamber that you wish to delay.

If you have been using reverb from a guitar amp or even most keyboard mixers you've probably noticed that it doesn't really create the sound of natural ambience. That is because in a natural environment you have first the direct signal. Then comes what is called the first early reflection. That is the sound of the direct signal bouncing back at you off an opposite wall. It is called the first early reflection but in most natural environments there will most definitely be a second and even a third early reflections. The difference being not only the difference in delay time but the altered frequency response between all the early reflections. After the early reflections come many shorter echoes tapering in their envelope and then finally there is reverb. Reverb is made up of many finite echoes so dense it is impossible for the human ear to distinguish between them. We perceive these finite echoes as what we call reverb.

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early reverb reflections There are environments where reverb is not preceded by pre-delay ( early reflections ). An example of this would be your bathroom or actually mine. It's small and the reverb decay time ( the time it takes for the reverb to die off ) is short. In the bathroom the midrange frequencies of the direct signal are more present in the reverb and therefore have a longer decay time. This decay time factor gives sound created in a bathroom a very midrange type of quality. Our ear can recognize this quality and most of us can recognize a "bathtub" sound. In a gymnasium there are many early reflections before then reverb starts. The decay time is longer for the lower frequencies and they sustain longer than the higher frequencies. Knowing what frequencies are boosted and cut in different environments are essential for one who whats to be good at synthesizing reverb.

Many newer digital reverb units have a pre-delay section that precedes the reverb section. By delaying the time before the reverb starts, this simulates what early reflections do. Mastering the right delay time is essentially mastering pre- delay. Some of the other controls such as the rolloff section will help contour the frequency response of the reverbs decay. Rolling off certain higher frequencies will give change to the apparent decay time of the reverb.

To synthesize a more natural sounding reverb though, you're going to need a separate delay unit to feed your reverb chamber. When using a separate delay to recreate the early reflections, the careful use of feedback as well as equalization in the feedback loop will help make the reverb more natural. This will come close but with a single delay you can not come as close as the distinct differences in symmetrical timing of the early reflections.

Unfortunately, the cost of a most professional digital reverbs, with adjustable mid-range and low frequency decay times and excellent pre-delay features, are well above what most musicians would care to spend. They average in the 10,000 price range. But this is not to say that good reverb cannot be created with the lower priced digital reverbs averaging around just above the $1,000 price range. In the studio with careful adjustment all the reverb units on the market can yield great effects.

The use of pre-delay can add clarity to a instrument while giving it a depth dimension. Just adding reverb to an instrument can muddy up the sound. The trick is not to add the same amount of pre-delay to all the instruments in a mix or live on stage. You can have only one reverb chamber but if you delay each instrument differently before you send it to the chamber each instrument will have more of its own dimension.

Having many different delays and chambers will yield even more clarity. With one digital delay and one digital reverb you can have two different dimensions and a additional dimension for each additional effect added. This is achieved by sending some instruments to the delay effect and the other instruments to the effect. If you send the same instrument to both effects simultaneously, it takes something away from the mix. This is not to say that you can't send an istrument to both effects, but it should be thought out and executed ever so carefully. This will ensure clarity in the mix. If you have the channels on your mixer, try returning an instrument to two channels and equalize each channel differently. Then feed only one channel direct to the mix and the heavily eq'd one to your reverb chamber. This technique is called pre-chamber equalization.

Most mixers have at least two sends. If you add more effects they will have to be assigned to a specific instrument and patched before that instrument returns to the mixer. Some mixers have effect loops on every channel and therefore allow patching at that point.

The new MIDI digital reverbs as well as the MIDI digital delays, both with internal preset memorys, are the most economical way to get a arsenal of effects without spending a fortune. With one MIDI reverb and delay the pre-delay, the reverb decay and the feedback of the delay can be programmed to change via midi with your keyboard patches. You could even assign each unit primarily to separate keyboards and this way get more clarity between the different parts in a tune by changing memory patches of the effect unit via midi, within the tune, with each keyboard's patches.

Use the decay of your reverb unit to suit different instruments. For example , for a bass sounds, stay away from long reverb decay times. With thin sounds and primarily high pitched sounds, long reverb times can be most unpleasant for the listener. In general if you would like to use a long reverb decay time, use a decent amount of pre-delay time. This is especially true with fast passages. In this way, notes don't seem to melt into each other.

And never, never put the cat in the microwave .. see you next month!

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