STOMPBOX DESIGN WORKSHOP - CCRMAesteban/stompbox/2015/2015_Stompb… · STOMPBOX DESIGN WORKSHOP...

FX Basics

Dynamics Effects

STOMPBOX DESIGN WORKSHOP

Esteban Maestre

CCRMA - Stanford University August 2015

FX Basics: Dynamics Effects

Dynamics effects were the earliest effects to be introduced by guitarists.

The simple idea behind dynamics effects is to amplify or attenuate the amplitude of the electrical signal coming out from the pickup or microphone.

They first appeared in the 1940s as simple on/off switch boards, evolving to volume pedals in the 1950s.

Ex: volume pedal, boost, tremolo, noise gate, dynamic range compressor

Gain control

0.05 0.055 0.06 0.065

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0.05 0.055 0.06 0.065

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FX Basics:Dynamics Effects

XInput signal Output signal

Gain

Gain > 1

Achieved by means of a simple multiplication.

Volume BoostFX Basics:

Dynamics Effects


Gain ON/OFF

Generally used for boosting volume during solos and/or preventing signal loss in long effect chains.

Ex: when switching from rhythm guitar to lead guitar, a guitarist may use a clean boost to increase the volume of his or her solo.

Volume Boost (ii)FX Basics:

Dynamics Effects

0.68 0.7 0.72 0.74

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seconds

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0.68 0.7 0.72 0.74

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0.68 0.69 0.7 0.71 0.72 0.73 0.74

-0.5

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0.5

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1.5

seconds

OF

F/O

N

0.68 0.69 0.7 0.71 0.72 0.73 0.74

-0.5

0

0.5

1

1.5

seconds

gain

X

00_stomp_dynamics_1.pd

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 24

4.5

5

5.5

6

seconds

LF

O f

requency

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 21

1.5

2

seconds

LF

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mplit

ude

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-2

-1

0

1

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seconds

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sig

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TremoloFX Basics:

Dynamics Effects

X

Output signal

Produces a slight, rapid oscillation of the signal amplitude; not to be confused with tremolo bar (pitch oscillation).

Based on the use of a Low Frequency Oscillator (LFO):

~

FREQUENCY (f0) AMPLITUDE

Oscillator

LFO

1/f0

Tremolo (ii)FX Basics:

Dynamics Effects


ON/OFF

Typically, two controls are offered:RATE: Sets the frequency of the volume oscillationDEPTH: Sets the amplitude of the volume oscillation

LFO

AmplitudeFrequency

+

1

RATE DEPTH

Tremolo (iii)FX Basics:

Dynamics Effects

0 0.5 1 1.5 2-1

-0.5

0

0.5

1

seconds

input

0 0.5 1 1.5 24

5

6

7

8

seconds

LF

O f

requency

0 0.5 1 1.5 20.1

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secondsLF

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ude

0 0.5 1 1.5 2-1

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seconds

outp

ut

0.62 0.625 0.63 0.635 0.64 0.645 0.65 0.655-1

-0.5

0

0.5

seconds

input

X

Inputsignal

Outputsignal

ON/OFF

AmplitudeFrequency

+

1

RATE DEPTH

LFO


Noise gateFX Basics:

Dynamics Effects

Attenuates signal when its level falls below a given threshold. Both the attenuation and threshold are usually available as user controls (resp. RANGE and LEVEL).

Ex: avoid unwanted noise floor when there is no signal coming from the instrument

X

Input Signal

OutputSignal

LEVEL

Level Detector

RANGE

< ?

Noise gate (ii)FX Basics:

Dynamics Effects

LEVEL DETECTOR (Envelope Follower):

Often implemented as Root Mean Square (RMS) meter. RMS amplitude provides a measure of effective (short-time averaged) signal intensity.

‘Averaging time’ sets the responsiveness of the meter.

Input Signal

OutputSignal

AVG. TIME

AVG^2 SQRT

RMS ENVELOPE FOLLOWER


TIME AVERAGE

Acts as a smoothing function:

Smoothing Function Output

Signal

y[n]x[n]

InputSignal

n

x

n

y

n n

Current sample

Current sample

Average of current and previous input samples


SMOOTHING WITH RECURSIVE EQUATION:

Find coefficients a and b so that equation

y[n] = b0·x[n] + b1·x[n-1] + … + bN·x[n-N]

- a1·y[n-1] - … - aN·y[n-N]

results into a smoothing function.

…digital implementation of a Low Pass (LP) filter.

current and previous input samples

previous output samples

TIME AVERAGE:

y [n] = ( 1/M ) · ( x[n] + x[n-1] + … + x[n-M+1] + x[n-M] )

Obtain M from ‘averaging time’ : M = avgTime · fs


RMS Envelope…

With TIME AVERAGE:

With Smoothing Low-Pass Filter (RECURSIVE):

0.3 0.35 0.4 0.45 0.5

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0.3 0.35 0.4 0.45 0.5 0.55-1

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seconds

Averaging using 441 and 882 previous samples respectively(M=441; M=882)

Both filters only using1 previous sample(N=1) !!


0.564 0.566 0.568 0.57 0.572 0.574 0.576 0.578 0.58

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TIME DOMAIN

1/1200 1/500

0 0.5 1 1.5 2 2.5

x 104

0

0.2

0.4

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0.8

1

magnitude

frequency (Hz)

FREQUENCY DOMAIN

Fourier Transform

500 1200

fs/2 (Nyquist)


0.366 0.367 0.368 0.369 0.37 0.371 0.372 0.373 0.374 0.375

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x(t) = 1.0·sin(2·π·500·t) + 0.4·sin(2·π·5000·t)

0 0.5 1 1.5 2 2.5

x 104

0

0.5

1

1.5

magnitude

frequency (Hz)

5005000


f

Magnitude

Slower Components

fs/2 (Nyquist)

Quicker Components

Low Frequencies

High Frequencies


f

Gain

Low Frequencies

High Frequencies

1 One can design a Low-Pass filterso that components above a certain ‘characteristic’ frequency (fc) get attenuated…

LP


y[n] = 0.0344·x[n] + 0.0344·x[n-1]

+ 0.9312·y[n-1]

0 0.5 1 1.5 2 2.5

x 104

0

0.2

0.4

0.6

0.8

1

magnitude

frequency (Hz)

5005000

0.382 0.383 0.384 0.385 0.386 0.387 0.388 0.389 0.39 0.391

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How to ‘design’ the coefficients?(e.g. how many coefficients? which values?)

Basics of DIGITAL FILTERS (to come…)

Noise gate (iii)FX Basics:

Dynamics Effects

RMS Envelope Follower

x[n] y[n]LP filter^2 SQRT

RMS ENVELOPE FOLLOWER

0.3 0.31 0.32 0.33 0.34 0.35

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0.1

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0.6

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seconds

Rapid oscillation (quicker components) have been attenuated

Noise gate (iv)FX Basics:

Dynamics Effects

Input

TH

Output

TH

Gain1

RANGEON ON

ON

Chattering

Abrupt ON-OFF / OFF-ON transitions

Example of basic operation

Noise gate (v)FX Basics:

Dynamics Effects

Input

THON-OFF

THOFF-ON

Avoids chattering

Gain

Output

1

RANGE

Release

Attack

Smoother transitions


Noise gates often include HYSTERESIS and ATTACK/RELEASE times

Dynamic Range Compressor


Attenuates the signal when its level its higher than a certain threshold. Both the amount of attenuation and the threshold are the most typical user controls (resp. COMPRESSION/RATIO and LEVEL).

Ex: reduce intensity differences, soften the amplitude of very loud attacks

X

LEVEL

Level Detector

COMPRESSION

>?

InputLevel

Output Level

LEVEL

COMPRESSION

Bypass

Hard Limiter

Dynamic Range Compressor (ii)


X

LEVEL

Level Detector

COMPRESSION

FEED-FORWARD basic structure

Gain Computer

X

LEVEL

Level Detector

COMPRESSION

FEED-BACK basic structure Gain

Computer

Dynamic Range Compressor (iii)


Example of basic operation

InputLevel

Output Level

LEVEL

OFF: Gain = 1

ON: Gain < 1

1:1

2:1

4:1

Inf:1

Gain = 1

Gain < 1

ONOFF OFF OFFON

Input

Output

Gain

Dynamic Range Compressor (iv)


Further available controls, depending on application:

• ATTACK / RELEASE TIMES

• HARD vs SOFT KNEE

• MAKE-UP GAIN

InputLevel

Output Level

LEVEL

SOFT KNEE

MAKE-UP GAIN

HARD KNEE

Make-up Gain

Reduced Gain

ONOFF OFF OFFON

Input

Output

Gain


STOMPBOX DESIGN WORKSHOP - CCRMAesteban/stompbox/2015/2015_Stompb… · STOMPBOX DESIGN WORKSHOP...

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