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Post Index » STAGE TECHNIC » Pro Sound


Media College (Chương 1 : Âm Thanh) (5,6) - Page 5 PDF Print E-mail
Written by tuyenphuc   
Monday, 15 March 2010 17:15
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Reverb Effects

Reverberation can be added to a sound artificially using a reverb effect. This effect can be generated by a stand-alone reverb unit, the reverb effect in another device (such as a mixer or multi-effects unit), or by audio processing software.

There are three possible reasons for adding reverb:

  1. To restore the natural sound as the listener would expect to hear it. For example, a recording done in a very low-reverb studio might sound unnatural unless reverb is added.
  2. To enhance the sound. For example, it is common to give vocal recordings more reverb than what would be considered natural. Reverb helps fill out the voice, giving it more "body" and is usually considered to be a flattering effect. Reverb can even help smooth minor vocal fluctuations so they aren't as obvious.
  3. To create special effects such as dream sequences, etc.

Reverb is the most common audio effect, partly because it is used in so many situations from music studios to television production. Every sound operator should have a good understanding of reverb and how/when to apply it.

It pays to be judicious with reverb. Because it is so effective, it can easily be over-used. The right amount of reverb can do wonders for a singer's voice but too much sounds silly.

Examples

The photo below is a rack-mountable Lexicon PCM 81 Digital Effects Processor. This unit has a number of effects including reverb.

90

The screenshot below is from Adobe Audition, a sound editing package. It gives you an idea of some of the common reverb settings. Notice how most of the presets are described by the real-world effect they are simulating, for example, "Concert Hall" and "Medium Empty Room". This is common in reverb units.

91

Examples of Reverb

The following examples show how the reverb effect works. The first example is dry, meaning that it has no effects or other processing applied. The next two examples have different levels of reverb applied.

  • Drums - Dry
  • Drums - Medium Reverb
  • Drums - Hall

Chorus

The chorus effect is designed to make a signal sound like it was produced by multiple similar sources. For example, if you add the chorus effect to a solo singer's voice, the results sounds like.... a chorus.

Chorus works by adding multiple short delays to the signal, but rather than repeating the same delay, each delay is "variable length" (the speed and length of the delay changes). This adds the randomness required for the chorus sound. Varying the delay time also varies the pitch slightly, further adding to the "multiple sources" illusion.

The chorus effect was originally designed to make a single person's voice sound like multiple voices saying or singing the same thing, i.e. make a soloist into a chorus. It has since become a common effect used with musical instruments as well.

The effect is a type of delay — the original signal is duplicated and played at varying lengths and pitches. This creates the effect of multiple sources, as each source is very slightly out of time and tune (just as in real life). Technically, a chorus is similar to a flanger.

Common parameters include:

Number of Voices:

The number of times the source is multiplied.

Delay:

The minimum delay length, typically 20 to 30 milliseconds.

Sweep Depth/ Width:

The maximum delay length.

The following example is the chorus settings window in Adobe Audition.

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Phasing & Flanging

Phasing, AKA phase shifting, is a sweeping, whooshing effect often used in music. The effect is created by mixing the original signal with another version of itself which has been phase-shifted. This results in various out-of-phase interactions over time which gives the sweeping effect.

Phasing is created by adding evenly-spaced notches in the frequency response and moving them up and down the frequency spectrum.

Flanging is a specific type of phasing which uses notches that are "harmonically related", i.e. related to musical notes.

Phase Shifting (Phasing)

Phase-shifting, AKA phasing, is an audio effect which takes advantage of the way sound waves interact with each other when they are out of phase. By splitting an audio signal into two signals and changing the relative phasing between them, a variety of interesting sweeping effects can be created.

The phasing effect was first made popular by musicians in the 1960s and has remained an important part of audio work ever since.

Phasing is similar to flanging, except that instead of a simple delay it uses notch and boost filters to to phase-shift frequencies over time.

The following examples show some of the different types of phasing effects (MP3):

  • Drums: Dry (original audio with no effect)
  • Drums: Phased
  • Drums: Crunchy Phase
  • Drums: Trebly Phasing
  • Drums: Bassy Phase
  • Drums: Tremolo Phasing Left to Right
  • Drums: Washy Phase Left to Right
  • Drums: "Bubbles" Phase

The screenshot below is from Adobe Audition and shows some of the common settings available in phasing effects.

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Flanging

Flanging is a type of phase-shifting. It is an effect which mixes the original signal with a varying, slightly delayed version of the signal. The original and delayed signals are mixed more or less equally.

Flanging results in a sweeping sound — see the following example (MP3):

  • Drums: Dry (original audio with no effect)
  • Drums: Flanged

The term flanging comes from the days of reel-to-reel tape recording. The original signal was recorded on a second reel, and the delay was achieved by holding a finger or thumb on the edge (flange) of the reel to physically slow it down. Flanging was made popular during the psychedelic music era in the 1960s and 1970s.

The following example is the flanger settings window in Adobe Audition. It shows some of the settings commonly used in flanging:94

(Xem tiếp phần 7: Màu sắc âm thanh, Noise, Colours & Types).





 

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