My own interest in electronic music and its production has naturally lead me to research and learn the use of synthesizers both physical and in software. Synthesizers have existed since the 1960s and the market has developed and changed in many ways since then. The first synthesizers were massive modular analog machines, with individual modules that each played a role in the sound synthesis process, with the most notable example being the Moog synthesizer. In the 1970s these machines became very popular due to their unique and new sound and many companies like ARP and Dave Smith Instruments joined Moog in the market. Synths became much smaller and self contained in this decade and their popularity with touring musicians grew.
Dr Bob Moog explains how the Minimoog, and by extension analog synths, work.
In the 1980s Yamaha introduced the DX7, which was the first affordable and truly portable synth based on microchips that created the sounds digitally rather than with analog components. It used a technique known as frequency modulation (FM) synthesis which was able to accurately emulate the metallic and glassy sounds of bells, electric pianos, xylophones and other instruments. This was a large tonal shift from its analog predecessors which could only create warm, often imperfect sounds that were closer to string and brass instruments. The digital nature of the DX7 meant that it never suffered from the tuning issues that often plagued its analog counterparts, enabling its "operators" to reproduce the same sound perfectly every time a note was played. FM synthesis is significantly more complex than the subtractive synthesis analog synths use and the interfaces of the machines that used it made it quite difficult to program sounds in. As such, most keyboardists just used the pre programmed sounds rather than making their own. The industry took note of the enormous success of this synth and soon most companies were trying to emulate its digital circuitry or stripped back, barren interface, with varying degrees of success.
This video showcases the sounds of the DX7, many of which should be instantly recognizable.
Eventually, producers began to tire of the cold, often thin sounds of FM synthesis, which by the end of the 80s was everywhere in pop music. Companies responded in the 1990s by trying to emulate the warm, more organic sounds of analog with digital circuitry. Using DSP, "Virtual Analog" synthesis was developed. Analog circuits of old were recreated on a microprocessor to produce those sought after sounds with much more reliability and more sonic potential. Many VA synths grew to define entire genres of electronic music, with Roland's JP8000 keyboard's "supersaw" becoming the defining sound of Trance music.
The Roland JP-8000, a VA synth, in action
With these emulations of classic sounds becoming so widespread, newer producers began to rediscover the synths that created them in the first place and began to realize how poorly many VA sounds measured up. Sure the sound design experience and essential sonic characteristics were faithfully recreated, but due to the limits of DSP and digital to analog conversion at the time, VA synths still had many of the same sonic issues that pulled people away from FM synths. This rediscovery of analog in the 2000s lead to many companies moving back to making analog synths and away from VA. There are also quite a few synths that use a mixture of digital and analog components that can get quite close to the sound quality of purely analog hardware.
The Moog Matriarch, released in 2019, is a fully analog synth with a design and sound that is reminiscent of its predecessors from the 1970s.
Through my experimentation with all 3 of these synthesis methods I have discovered aspects of all that I want to incorporate into my own synthesizer. FM synths require extremely stable oscillators to produce the clean sounds they're known for and as such, most analog components are just not suitable for it. Most modern virtual analog, and some true analog synths have very simple FM controls that add dimension to the sound but don't have the same capabilities as a true FM synth. My solution aims to recreate true FM synthesis with the minimum necessary digital components to deliver a sound that has the best of both analog and digital. As I mentioned before, FM synths are based on a series of "operators" which are essentially complex oscillators (the DX7 has 6 of these) that generate sine waves of various frequencies. The outputs of these operators are then used to modulate the frequencies of other operators in patterns known as "algorithms". The operators that produce sound are called carriers, and those that modulate the carriers are called modulators. Because the frequency output of the operators is used for modulation, said frequency needs to be as stable as possible to produce a consistent sound, which is why digital is preferred over analog for this technique.
I have taken a hybrid approach to this issue, using both analog and digital components. My synth will use 6 digital signal generators to produce all of the commonly used waveforms for synthesis instead of just sine waves as well as envelopes that can be used for modulation. From that point forward the signal path of the synth will be entirely analog with and analog filter and amplifier stage coming right after the sound generation. The filter cutoff and amplifier amplitude can be controlled digitally which allows for modulation from one or more of the signal generators. The user will have the option to select which signal generators behave as sound sources, and which behave as modulation sources. This flexibility will let the user choose to either use traditional subtractive synthesis to make a sound or opt instead for an FM algorithm. The user will have the option to keep the oscillators stable to produce a conventional FM sound or to simulate the instability inherent in analog hardware. All of the waveforms will be modeled on the output of real analog oscillators which are more pleasing and less mathematically correct. The synth will be polyphonic, meaning that multiple notes can be played simultaneously. This will require the analog portion of the circuit to be replicated multiple times. The goal for this will be 8 voices, meaning that 8 analog voice boards will be needed to be built per synth. The interface of the synth will consist of knobs for controlling various parameters and a single central screen that can be used to display relevant information. The synth can be played with either a MIDI keyboard plugged directly in or controlled by a computer running a digital audio workstation or some other software that can process MIDI information. Sound will be sent out through a stereo pair of 1/4 in TS jacks, which is the industry standard configuration for a synth with a stereo signal. The complex nature of the DSP and many analog voice boards will mean this synth will be expensive to develop and produce so it will have to command a high price tag in the $2000-3000 range. While this seems like a lot for a synth, and there are many purely analog synthesizers that are sold for under $2000, the flexibility and power of this instrument will be worth the upfront cost to the user. Cut down versions with fewer voices and operators can be produced and sold as well.