4 subtraktivna sinteza -...
TRANSCRIPT
Subtrak(vna sinteza • Filtriranje signala bogatog spektra • Najčešće su to signali testerastog ili četvrtastog oblika u vremenskom domenu
• Vrhunac upotrebe u analognim sin(sajzerima 60ih i 70ih godina XX veka
• Analognom elektronikom simuliran način generisanja zvuka u akus(čnim intstrumen(ma
• Govorni mehanizam
Subtrak(vna sinteza • Analiza rada akus(čnih instrumenata: sistem ekscitator-‐oscilator-‐rezonator.
• Simulacija ovog sistema u elektroakus(čko analognoj izvedbi.
• Specifična vrsta “fizičkog modelovanja” – termin sa kraja XX veka
Blok šema
• Oscillators: Generate the basic signal. This is usually a waveform that is rich in harmonics Many synthesizers offer more than one oscillator.
• Filter sec.on: Used to alter the basic signal by filtering out (removing) por(ons of the frequency spectrum. Many synthesizers offer a single filter, which is applied universally to all oscillator signals. Mul(oscillator synthesizers can provide mul(ple filters, allowing each oscillator signal to be filtered in a different way
• Amplifier sec.on: Used to control the level of the signal over (me. The amplifier features a module known as an envelope, which is broken down into several elements that provide level control for the beginning, middle, and end por(ons of your sound. Simple synthesizers generally offer a single envelope, which is used to control the oscillator (and filter) over (me. More complex synthesizers can feature mul(ple envelopes
• Modula'on and Control Components • Modulators: Used to modulate the signal-‐genera(ng and processing components.
Modula(ons can be machine-‐based—automa(cally generated by a synthesizer component—or can be manually ac(vated by using the modula(on wheel, for example. Most synthesizers provide a component called an LFO(low frequency oscillator) to provide a waveform that modulates the signal.
• Global controls: Affect the overall characteris(cs of your synthesizer sound, such as glides between notes, pitch bend, monophonic or polyphonic playback, and more
Subtrak(vna sinteza
• Na početku lanca: Naponski kontrolisan oscilator (VCO – Voltage Controlled Oscilator)
• Generiše signal širokog spektra
Sawtooth – testeras( oblik signala jasan i svetao zvuk pogodan za generisanje žičanih, duvačkih i sl.
zvukova
Square i Pulse Waves • Square and Pulse Waves • Hollow and woody-‐sounding, a square wave can contain a
wide range of odd harmonics. It is useful when crea(ng reed instruments, pads, and basses. It can also be used to emulate kick drums, congas, tom-‐toms, and other percussive instruments—oaen blended with another oscillator waveform, such as noise.
• The square wave can be reshaped to make the waveform cycles—or pulses—more rectangular on many synthesizers, using a pulse width modula(on (PWM) control. The more rectangular the wave becomes, the more nasal it sounds. When modulated in this way, the square wave is known as a pulse wave, and contains fewer harmonics. It can be used for reeds, basses, and brass sounds.
Sqare i Pulse Wave
Triangle Like a square wave, a triangle wave contains only odd harmonics. Because a triangle wave’s higher harmonics roll off faster than the ones of a square wave, the triangle wave sounds soaer. It is ideal for crea(ng flute sounds, pads, and vocal “oohs.”
Noise is useful for emula(ng percussive sounds, such as snare drums, or wind and surf sounds, among others. White noise: The most common noise waveform found on synthesizers. White noise contains all frequencies—at full level—around a center frequency. Pink and red noise: These noise colors also contain all frequencies, but they are not at full level across the frequency spectrum. Pink noise decreases the level by 3 dB per octave (of higher frequencies). Red noise decreases the level by 6 dB per octave. Blue noise: Blue noise, which is the reverse of pink noise, increases the level of all frequencies in higher octaves by 3 dB. There are other noise wave colors, but they aren’t commonly found in synthesizers.
Square pulse
Četvrtka – Square Pulse (50% -‐ 50%)
Filtriranje -‐ kontrola boje tona
Filtri oduzimaju (subtract) određeni deo kompleksnog spektra kako bi se došlo do željene boje tona
Sawtooth nefiltriran Sawtooth filtriran lowpass filtrom, fc = 2.5kHz. Poprima oblik sinusoide, ton postaje mekši, manje metalan...
Realni filtri – rezonansa (zvonjava)
Resonansa The resonance control emphasizes or suppresses signals around the cutoff frequency. The figure below shows an ES1 sawtooth wave with a high resonance selng and the cutoff frequency set to 660 Hz, which is about 60%. This resonant filter selng results in much brighter and harsher signals close to the cutoff frequency. Frequencies below the cutoff point are unaffected. Once again, the overall result of using filter resonance is a change in the basic waveform’s shape and, therefore, its (mbre. Very high filter resonance selngs can be used to such an extreme degree that the filter begins to self-‐oscillate, resul(ng in the filter genera(ng a sine wave.
Drive Drive adds an amount of gain to the waveform as it enters the filter—an input gain control—thus overdriving the filter and distor(ng the waveform. This waveform distor(on changes the (mbre of the sound, making it much harsher.
Slope (Strmina filtra) filter will cut off the signal at the set cutoff frequency. This cutoff doesn’t happen abruptly but rather at a given slope, which is measured in decibels (dB) of gain reduc(on per octave. Put another way, you can define how steep the “cliff” is at the cutoff point by choosing a rela(vely severe or more gentle slope.
• Proces filtracije može bi( kontrolisan niskofrekvencijskim oscilatorom (Low Frequency Oscillator – LFO) ili generatorom anvelope (Envelope Generator – EG)
• Modulacija boje • Using the Envelope to Control Filters • Envelope generators are not limited to controlling signal amplitude. They can also control the rise and fall of the filter cutoff frequency or modulate other parameters. In other words, envelope generators can be used as a modula(on source—or as a “remote control” for a given parameter, if you prefer.
ADSR
ADSR The envelope generator usually features four controls—anack, decay, sustain and release, commonly abbreviated as ADSR. A>ack: Controls the (me it takes for the ini(al slide from an amplitude of zero to 100% (full amplitude). Decay: Determines the (me taken for the subsequent fall from 100% amplitude to the designated sustain level. Sustain: Sets the steady amplitude level produced when a key is held down. Release: Sets the (me it takes for the sound to decay from the sustain level to an amplitude of zero when the key is released. If a key is released during the anack or decay stage, the sustain phase is usually skipped. A sustain level of zero will produce a piano-‐like—or percussive—envelope, with no con(nuous steady level, even when a key is held.
Izlazni pojačavač
• Naponski kontrolisani pojačivači • Takođe može bi( kontrolisan niskofrekvencijskim oscilatorom (Low Frequency Oscillator – LFO) ili generatorom anvelope (Envelope Generator – EG) – amplitudska modulacija
Modulacija • Modula'on • Without modula(on, sounds tend to be boring and fa(guing to the ear. They also
sound synthe(c, rather than natural, in the absence of some type of sonic modula(on. The most obvious type of modula(on is vibrato, which is used by orchestral string players to add anima(on to an instrument’s pitch.
• To make sounds more interes(ng, you can use various synthesizer controls to modulate basic sound parameters.
• Modula'on Rou'ng • Many synthesizers, including the ES1, ES2, and EXS24 mkII sampler, feature a
modula(on router. • The router allows you to direct one or more modula(on sources to one or more
modula(on targets—or des(na(ons, if you prefer. For example, you can change modula(on targets, such as the oscillator pitch or filter cutoff frequency, by using modula(on sources that include the following:
• Velocity modula;on: The impact of your keyboard playing (harder or soaer). • Key scaling: The posi(on you play on the keyboard. • Use of controls: These can include the modula(on wheel, ribbon controllers, or
pedals anached to your keyboard. • Automa;c modula;on: You can use envelope generators or LFOs to modulate
signals automa(cally.
• Modula'on Controllers • Modula(on sources can be—and oaen are—triggered by something you’ve done, such as played a note on the keyboard, or moved the modula(on wheel.
• Thus, the modula(on wheel, pitch bend ribbons, foot pedals, keyboard, and other input op(ons are referred to as modula;on controllers, or simply controllers.
• Perhaps the best example of a modula(on controller in ac(on would be the use of a velocity-‐sensi(ve keyboard, set up to control the filter and level envelopes. The harder you strike the notes, the louder and brighter the sound is.
Using the LFO to Modulate Sounds
• A modula(on source found on nearly all synthesizers is the LFO (low frequency oscillator). This oscillator is used only as a modula(on source and does not generate any audible signals that form part of your actual synthesizer sound, because it’s too low to be heard. It can, however, affect the main signal by adding vibrato, filter sweeps, and so on.
LFO Controls • The LFO generally offers the following controls:
• Waveform: Allows you to choose the type of waveform (triangle waves and square waves are seen most oaen). Triangle waves are useful for filter sweeps (slow changes to the filter cutoff frequency) or when simula(ng an ambulance siren (slow changes to the oscillator frequency). The square waveform is useful for rapid switches between two different pitches (vibratos or octaving, for example).
• Frequency/Rate: Determines the speed of the waveform cycles produced by the LFO. When set to low values, very slow ramps are produced, making it easy to create sounds such as ocean waves rolling in (when white noise is chosen as the waveform in the main oscillator).
• Sync mode: Allows you to choose between free running (a user-‐defined LFO rate) or synchroniza(on with an external tempo source (such as a host applica(on).
LFO Envelopes • The LFO can also be controlled with an envelope
generator in some synthesizers. As an example of where this might be useful, imagine a sustained string sec(on sound where vibrato is introduced a second or so into the sustained por(on of the sound. If this can happen automa(cally, it allows you to keep both hands on the keyboard.
• In certain synthesizers, a simple envelope generator is included for this precise purpose. Oaen, this envelope consists only of an anack parameter, or occasionally it includes decay or release op(ons. These parameters perform in the same fashion as the amplitude envelope parameters, but they are limited to control of LFO modula(ons.
Using Envelopes for Modula'on • The main envelope generator of the
synthesizer not only controls levels over (me, but it also is oaen used to modulate other sound parameters when you press or release keyboard keys.
• The most common use of envelope modula(on is to control the filter cutoff and resonance parameters with the keyboard velocity or keyboard scaling modula(on sources
• Digitalna tehnologija znatno olakšale i poboljšala kontrolu parametara u procesu subtrak(vne sinteze
• Osnovna mana je limi(ranost definisana vrstom i kvalitetom korišćenih oscilatornih i filterskih kola
• Adi(vna i subtrak(vna sinteza su linearni procesi: kombinovanjem ova dva postupka i uvođenjem nelinearnos( se proširuju mogućnos( sinteze.
Linkovi
• hnp://www.synthfe(sh.com/2010/07/subtrac(ve-‐synthesis-‐tutorial.html
• hnp://documenta(on.apple.com/en/logicexpress/instruments/index.html#chapter=A%26sec(on=3%26tasks=true
• hnp://blog.dubspot.com/video-‐tutorial-‐building-‐instruments/