FX Basics. Dynamics Effects STOMPBOX DESIGN WORKSHOP. Esteban Maestre. CCRMA Stanford University July 2011

Transcription

1 FX Basics STOMPBOX DESIGN WORKSHOP Esteban Maestre CCRMA Stanford University July 2

2 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 94s as simple on/off switch boards, evolving to volume pedals in the 95s. Ex: volume pedal, boost, tremolo, noise gate, dynamic range compressor

3 Gain control Achieved by means of a simple multiplication. Gain Input signal X Output signal amplitud de Gain > amplitud de

4 Volume Boost 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. Gi Gain ON/OFF Input signal X Output signal

5 Volume Boost (ii).5.5 gain.5 OFF/ON amplitude X amplitude _stomp_dynamics_.pd

6 Tremolo Produces a slight, rapid oscillation ofthe signal amplitude; not to be confused with tremolo bar (pitch oscillation). Based on the use of a 6 Low Frequency Oscillator (LFO): FREQUENCY (f ) AMPLITUDE y LFO frequency ~ Oscillator LFO X Output signal LFO amplitude LFO output signal amplitude /f 2 - /f

7 Tremolo (ii) Typically, twocontrols areoffered: RATE: Sets the frequency of the volume oscillation DEPTH: Sets the amplitude of the volume oscillation RATE DEPTH ON/OFF Frequency Amplitude LFO + Input signal X Output signal

8 Tremolo (iii) Input signal input RATE DEPTH ON/OFF Frequency Amplitude LFO + Output signal X input LFO amplitude LFO frequency _stomp_dynamics_2.pd output

9 Noise gate Attenuates signal whenits 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 floorwhenthere is nosignal coming from the instrument RANGE LEVEL Input Signal Level Detector X <? Output Signal

10 Noise gate (ii) 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 AVG. TIME ^2 AVG SQRT RMS ENVELOPE FOLLOWER Output Signal

11 TIME AVERAGE Acts as a smoothing function: x x[n] Input Signal Smoothing Function y[n] Output Signal y n Average of current and previous input samples n n n Current sample Current sample

12 TIME AVERAGE: y [n] = ( /M ) ( x[n] + x[n ] + + x[n M+] + x[n M] ) Obtain M from averaging time : M = avgtime f s SMOOTHING WITH RECURSIVE EQUATION: Find coefficients a and b so that equation y[n] = b x[n] + b x[n ] + + b N x[n N] a y[n ] [ a N y[n N] [ results into a smoothing function. digital implementation of a Low Pass (LP) filter. current and previous input samples previous output samples

13 RMS Envelope With TIME AVERAGE: Averaging using 44 and 882 previous samples respectively (M=44; M=882) With Smoothing Low Pass Filter (RECURSIVE):.5 Both fl filters only using previous sample (N=)!!

14 /2 /5 TIME DOMAIN litude ampl Fourier Transform FREQUENCY DOMAIN de magnitu f s /2 (Nyquist) frequency (Hz) x 4 5 2

15 x(t) =. sin(2 π 5 t) +.4 sin(2 π 5 t).5 amplitude magnitude frequency (Hz) x 4

16 Magnitude Slower Components Quicker Components f s /2 (Nyquist) Low Frequencies High Frequencies f

17 Gain One can design a Low Pass filter so that components above a certain characteristic frequency (f c ) get attenuated LP Low Frequencies High Frequencies f

18 y[n] =.344 x[n] 344 x[n] x[n ] 344 x[n ] y[n ] amplitude How to design the coefficients? (e.g. how many coefficients? which values?) magnitude Basics of DIGITAL FILTERS (to come ) frequency (Hz) x 4

19 Noise gate (iii) RMS Envelope Follower Rapid oscillation (quicker components).5 have been attenuated x[n] ^2 LP filter SQRT y[n] RMS ENVELOPE FOLLOWER

20 Noise gate (iv) Example of basic operation Input TH Gain RANGE ON ON ON Output Chattering TH Abrupt ON OFF / OFF ON transitions

21 Noise gate (v) Noise gates often include HYSTERESIS and ATTACK/RELEASE times Input Avoids chattering TH ON OFF TH OFF ON Gain RANGE Output Attack Release Smoother transitions 2_stomp_dynamics_3.pd pd

22 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 Bypass Level Detector COMPRESSION X LEVEL >? Output Level COMPRESSION Hard Limiter LEVEL Input Level

23 Dynamic Range Compressor (ii) COMPRESSION LEVEL FEED FORWARD basic structure Level Detector Gain Computer X COMPRESSION LEVEL FEED BACK basic structure Gain Computer Level Detector X

24 Dynamic Range Compressor (iii) Input Example of basic operation Output Level ON: Gain < : 2: 4: Gain Gain = Gain < OFF ON OFF ON OFF Inf: Output LEVEL OFF: Gain = Input Level

25 Dynamic Range Compressor (iv) Further available controls, depending on application: ATTACK / RELEASE TIMES HARD vs SOFT KNEE MAKE UP GAIN Input Output Level HARD KNEE Gain Make up Gain Reduced Gain OFF ON OFF ON OFF MAKE UP GAIN SOFT KNEE Output LEVEL 3_stomp_dynamics_4.pd Input Level