How does analog synthesizer work

Therefore, we don't hear it as a pitched sound, but as noise. Loudspeakers generate sound by moving a paper cone in response to current flowing through a magnetic voice coil attached to the cone. Thus, if you send a positive voltage into the loudspeaker, the cone moves forward. If you send a negative voltage, the cone moves backwards assuming the speakers are wired correctly.

If this voltage varies at a rapid periodic rate at a frequency within the range of human hearing , then the speaker will move air that corresponds to a musical tone. So, to generate a sound electronically, all we need to do is send a periodic voltage into a loudspeaker. By controlling the period of this voltage, we can create different frequencies - and yes, it really is that simple.

Getting back to synthesizers, the oscillator is the element responsible for generating the periodic waveform. Periodic waveforms are very easy to generate electronically; there are five basic waveforms commonly used with traditional analogue synthesizers. These waveforms consist of a fundamental frequency which gives a sound its sense of pitch and is where most of the audio energy is concentrated , and additional audio energy in the form of harmonics frequencies that are some multiple of the fundamental.

The more harmonics, the more high frequency energy, and the brighter the sound. Fewer harmonics means a duller sound. For precise information on the harmonic content of various waveforms, refer to any good book on acoustics; for information on the harmonic content of different instruments, see Howard Massey's book 'A Synthesist's Guide to Acoustic Instruments'.

For now, we will describe each waveform in terms of its sound quality. SINE: This waveform consists, in theory, of purely the fundamental ie. In practice, though, it's very difficult to generate a perfect sine wave, so there will usually be some very weak harmonics that add a slight 'buzz' to the sound. Whistling produces a waveform that is pretty close to a sine, as do guitar strings towards the very end of their decay especially if you're listening to the bass pickup with the tone control turned down.

Most audio test generators emit sine waves. It is often used to synthesize orchestral washes and monster bass parts. PULSE: Most pulse waves let you vary the duty cycle , or the percentage of time the pulse is high compared to the time the pulse is low see Figure 1. It is used a lot for percussive patches. Some synthesizers take short pieces of periodic waveforms sampled from existing instruments bass, piano, etc , store them digitally, and use these waveforms in place of the standard oscillator waveforms described above.

These digitally-stored or generated waveforms are not samples in the normal sense; to show why, consider a piano sound. The sound of a piano is very complex and varies considerably over time, so just grabbing a few cycles of the sound will not necessarily sound anything like a piano. However, you will end up with a 'natural-sounding' waveform that is unlike any of the five 'standard' waveforms described above.

Instruments like the Korg DW, Ensoniq ESQ-1, Kawai K3, Roland D50, and so on, offer multiple digital waveforms in place of, or in addition to, the standard synth waveforms; this translates into a greater variety of sound generators, which means more potential variety in your patches.

Most oscillators let you vary more than just the waveform. If the synth includes two oscillators, there will usually be a detuning control that alters the pitch of one oscillator with respect to the other oscillator. Sometimes you will also have the option of hard syncing one oscillator to the other.

This is a little complex to understand. With hard sync, a slave oscillator is always locked to the period of the master oscillator. Thus, even if you alter the frequency of the slave, it has the same apparent pitch as the master since the period remains constant; what does change is the harmonic content of the slave. Figure 2 shows how hard sync can provide unusual waveforms in the slave oscillator. The sound that's produced is very 'nasty' and harmonically complex.

Usually a standard organ-type keyboard controls the oscillator pitch although there are many alternate controllers other than the keyboard. However, just being able to control the pitch of an oscillator doesn't give us a very musical sound - we at least need some way to gate the sound on and off.

The simplest option is to simply hook up an amplifier after the oscillator Figure 3. When the key goes down, the gain is high and input signals are passed to the output; when the key is up, the gain is zero, so nothing makes it past the amplifier. This is a start, but we still need more control. The only instrument that cuts on and off like this is the organ; some instruments decay over time percussion, drums, plucked strings, etc , while some require a bit of attack time to reach full volume like woodwind, brass, and some bowed instruments.

What we need is some way to alter gain over time. One option would be to simply turn a knob that varies the gain of the output amplifier. Unfortunately, this method is neither fast nor repeatable, and requires that you use one of your hands on the knob instead of the keyboard.

A much better option is to use a Voltage-Controlled Amplifier VCA whose gain responds to a voltage applied to a special control terminal more voltage gives higher gain, less voltage gives lower gain.

Then all we need is a device that, in response to pressing a keyboard key, generates a series of voltage changes that alter the VCA gain exactly as we want. If the voltage ramps up slowly from full off to full on, the gain will increase slowly over time and produce an attack effect. If the voltage goes from full on to full off, we'll hear a decay. The circuit that generates this voltage change is called the envelope generator EG.

Normally, it produces no voltage; but as soon as you strike a key, this circuit leaps into action and generates a varying voltage to control the VCA. The most common type of envelope generator is the AD5R , so named because there are four voltage stages called Attack, Decay, Sustain, and Release.

Figure 4 shows the effect and timing of the various envelope parameters; refer to these as you read the following descriptions of the four basic parameters. Pressing a key initiates the attack phase, where the envelope output goes from full off to full on. This can take anywhere from a few milliseconds to a second or more, depending on the attack time control setting. After reaching maximum level, the decay phase kicks in. This determines how long it will take for the envelope to decay from its highest level down to the sustain level.

Setting the sustain to zero gives a signal that attacks and then decays down to nothing; this is called an AD for the two stages: Attack and Decay type of response.

Releasing the key initiates, not surprisingly, the release phase. This is the time it takes for the envelope to go from the sustain level back to zero. This envelope type offers more than just four stages, and while the sustain parameter is the same as that in the ADSR, attacks and decays are created by specifying a level you want the envelope to attain, and the rate of time it takes to reach that level. Figure 5 shows how using a six-stage version of this type of envelope can give a 'double attack' by setting a moderately fast rate to the maximum level of the first stage; a slower rate to a lower level in the second; a fast rate to almost the maximum in the third; a slower rate to the sustain level; and finally, a slow rate from the sustain level back to zero.

The end may be specified as an End level, or simply, a level setting of 00, depending on the make of synth. While more complex, these types of envelopes offer greater flexibility than the 'old standby' ADSR.

We'll talk about digital synthesizers later. Analog synthesizers generate their sounds by manipulating electric voltages. The oscillator shapes the voltage to produce a steady pitch at a given frequency, which determines the basic waveform that will be processed elsewhere in the synthesizer. The oscillator can be controlled by the keys similar to a piano keyboard, a revolving pitch wheel or another tool on the synthesizer's interface. The oscillator feeds the signal to the filter , and the musician turns knobs and dials to set parameters around the frequencies of a sound -- for instance, eliminating and emphasizing specific frequencies like we talked about earlier.

The sound passes from the filter to the amplifier , which controls the volume of the sound. The amplifier generally includes a series of envelope controls , which help determine the nuances in volume level over the lifespan of a note.

In an analog synthesizer, each of these pitch, tone color and loudness functions is organized into a module , or a unit intended for a specialized purpose. The earliest modules were encased in their own individual housings.

The oscillator is the initial sound source, like a piano string being struck. Voltage from a power source oscillates electrons which generates a waveform. Most synths let you select from various types of waves because different patterns have different sounds.

The most common types are: Sine, square, triangle and sawtooth. Frequency is the speed of the vibration. This is the frequency with which a waveform completes one cycle of its pattern. The faster the frequency, the higher the pitch. If you double the frequency the pitch goes up an octave.

So to put it in musical terms, a Hz tone is an A note, and Hz is an A an octave up. This is how you get different notes to play a melody. But a saxophone and guitar sound very different even when played at the same pitch.

This is where synthesisers alter and play with harmonics to create, emulate and invent sounds. A sine wave is just one single frequency, but all other sounds are made up of several frequencies that combine to form the dominant pitch that you hear.

The filter section of a synthesiser modifies the timbre of the sound by blocking some frequencies in the waveform and letting others pass. Turning the filter knob from top to bottom gives you the recognisable sweeping sound from bright to dull or silent. Amplifiers control volume by making a signal bigger and therefore louder. But it can also modify the amplitude of the signal over time, for example, how quickly it reaches full volume, and how long it sustains that volume.

As an example, imagine the difference between the short sound you get from a xylophone compared to a long sustained note being played by a saxophone.