SIGNAL PROCESSING

(TIME-BASED EFFECTS)

Delay, Modulation and Reverb effects

WHY DO WE PROCESS SOUND FOR RECORDINGS AND LIVE MUSIC PERFORMANCES?

Signal processing is used to mold and shape the sounds that are used in an audio recording.

All commercial recordings and

professional live performances make extensive use of signal processing.

BASIC RULES THAT RELATE TO SOUND PROCESSING: Effects are best employed when the user

actually understands what the effect really does to the sound.

Don’t over process sounds unnecessarily (less is more)

Applying effects should not make up for poor microphone technique and equalization

Effects will not substantially improve a weak composition, arrangement or performance.

EFFECTS PROCESSORS CAN BE HOOKED UP IN THREE DIFFERENT WAYS:

In-line: The signal is sent directly into the unit from an instrument and then right into a mixer or amplifier.

Effects loop: Connection to the send and return (effects or aux) bus on a mixer or amplifier. This method is used if we want to add the same effect to a variety of different channels or parts at the same time. Example: Reverb

Insert: Inserted into a channel strip of a mixer.

TYPICAL SIGNAL PATH:

THERE ARE THREE MAIN TYPES OF TIME BASED EFFECTS:

Delay

Modulation

Reverb

DELAY A delay unit records a sound and then reproduces

the sound a little later.

Delay gives the listener the impression that the sound is being made in a larger environment. This is referred to as delay time or delay length. Delay time is usually measured in milliseconds (ms).

  There are 1000 milliseconds in a second.

In the early days of recording delay was created with tape loops. These days delay effects are created digitally.

THE THREE BASIC TYPES OF DELAY:

Slap Back

Doubling

Repeated Delays

SLAPBACK

The simplest form of delay

Slapback is a single repeat of a sound (35 ms to 300 ms).

This effect is most commonly used to thicken a vocal or instrumental part.

DOUBLING

A doubling effect is created when delay time is set to less than 35ms.

This gives the impression that two people are performing a part in unison.

When doubling always use prime numbers for delay times (ex. 1, 3, 5, 7, 11, 13... etc). This yields better results when a recording is heard in mono.

REPEATING DELAYS

Repeating delays are achieved with the use of a regeneration control dial (feedback).

This dial feeds the delay signal back through the unit.

The higher the feedback the greater number of repeats.

CALCULATING DELAY REPEATS

Delay repeats should line up with the rhythmic groove of a song.

There is a simple formula to calculate the delay time that will repeat in quarter notes along with the tempo of a song.

60 000 bpm (beats per minute) = delay time per beat (quarter note) in milliseconds

DELAY TIME TABLE:Tempo in Beats per Minute Quarter Note Eighth Note Sixteenth Note Quarter Note Triplet Eighth Note Triplet

20 3,000 1,500 750 2,000 1,00025 2,400 1,200 600 1,600 80030 2,000 1,000 500 1,333 66735 1,714 857 429 1,143 57140 1,500 750 375 1,000 50045 1,333 667 333 889 44450 1,200 600 300 800 40055 1,091 545 273 727 36460 1,000 500 250 667 33365 923 462 231 615 30870 857 429 214 571 28675 800 400 200 533 26780 750 375 188 500 25085 706 353 176 471 23590 667 333 167 444 22295 632 316 158 421 211100 600 300 150 400 200105 571 286 143 381 190110 545 273 136 364 182115 522 261 130 348 174120 500 250 125 333 167125 480 240 120 320 160130 462 231 115 308 154135 444 222 111 296 148140 429 214 107 286 143145 414 207 103 276 138150 400 200 100 267 133155 387 194 97 258 129160 375 188 94 250 125165 364 182 91 242 121170 353 176 88 235 118175 343 171 86 229 114180 333 167 83 222 111185 324 162 81 216 108190 316 158 79 211 105195 308 154 77 205 103200 300 150 75 200 100205 293 146 73 195 98210 286 143 71 190 95

MODULATION

The modulation control on a delay unit is used to create other popular effects such as chorus, flanging and phase shifting.

These effects involve pitch variations that are created with a LFO (Low Frequency Oscillator) that continually varies the delay time.

Altering the range of delay time (depth) and the speed of change (speed) will create a great variety of modulation effects.

PHASE SHIFTING

Phase Shifting occurs when a delayed copy of a sound is heard directly after the original.

The two sounds are so close together that they almost cancel each other out.

This is known as phase cancellation. To achieve this effect the delay time is set from 0.2-2ms.

FLANGING

Flanging is a metallic effect that was originally created by playing two reel to reel tape recordings of the same tune simultaneously.

The engineer varied the speed of one of the tapes by touching the edges of the reel (“the flange”).

This created a short delay that varied anywhere from 10-20ms between the sounds. It is best used on Rhodes pianos and guitars.

CHORUS

Chorus attempts to simulate the time and pitch variation of a choir.

This works well on background vocals, guitars and keyboards.

The delay time is set anywhere between 15 and 35ms.

With the longer delay time we actually hear a noticeable pitch variation.

ENHANCING MODULATION EFFECTS

All of these modulation effects can create even more interesting results when they are used in stereo.

Most modern effects devices are available in stereo.

Quite often they will even turn a mono signal into a stereo processed sound.

 

REVERBERATION

Reverberation is really just a series delays.

Reverb devices attempt to simulate the sound of a specific acoustic environment.

Basically every modern recording and most live performances make extensive use of reverb to help make the music sound larger than life to the listener.

VARIABLES (DIALS) THAT CAN BE ALTERED ON A REVERB DEVICE TO SIMULATE AN ENVIRONMENT:

Pre-delay: time delay that happens before the reverb is heard.

Reflections: the number of times that a sound bounces around a room

Diffusion: amount of time between the reflections

Decay time: the amount of time it takes for a sound to decreases to one millionth of its original sound pressure level.

Density: the time spacing of the initial reflections.

MOST COMMON REVERB SETTINGS: Hall: smoothest and richest

Chamber: echo chamber

Plate: bright

Room: bedrooms to large conference rooms

Reverse: backwards effect

Gated: lots of reverb that is closed off quickly (Phil Collins drums)