Transcript Signal Processing

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:
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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:
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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:
Source
Equalization
Dynamic
Processor
•Microphone
•Instrument (DI)
•Parametric EQ
•Graphic EQ
•Wah
•Compressor
•Chorus
•Flanging
Modulation •Phasing
•Rotary
Effects
Spatial
Effects
Dynamic
Processor #2
•Delay
•Reverb
•Volume Pedal
•Noise Gate
THERE ARE THREE MAIN TYPES OF TIME
BASED EFFECTS:
Delay
Modulation
Reverb
DELAY
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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
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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
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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
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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
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
125
130
135
140
145
150
155
160
165
170
175
180
185
190
195
200
205
210
3,000
2,400
2,000
1,714
1,500
1,333
1,200
1,091
1,000
923
857
800
750
706
667
632
600
571
545
522
500
480
462
444
429
414
400
387
375
364
353
343
333
324
316
308
300
293
286
1,500
1,200
1,000
857
750
667
600
545
500
462
429
400
375
353
333
316
300
286
273
261
250
240
231
222
214
207
200
194
188
182
176
171
167
162
158
154
150
146
143
750
600
500
429
375
333
300
273
250
231
214
200
188
176
167
158
150
143
136
130
125
120
115
111
107
103
100
97
94
91
88
86
83
81
79
77
75
73
71
2,000
1,600
1,333
1,143
1,000
889
800
727
667
615
571
533
500
471
444
421
400
381
364
348
333
320
308
296
286
276
267
258
250
242
235
229
222
216
211
205
200
195
190
1,000
800
667
571
500
444
400
364
333
308
286
267
250
235
222
211
200
190
182
174
167
160
154
148
143
138
133
129
125
121
118
114
111
108
105
103
100
98
95
MODULATION
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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
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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
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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
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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
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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
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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:
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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:
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Hall: smoothest and richest
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Chamber: echo chamber
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Plate: bright
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Room: bedrooms to large conference rooms
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Reverse: backwards effect
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Gated: lots of reverb that is closed off quickly
(Phil Collins drums)