This section is written for the good old days: I was lucky to follow closely this industry when some amazing technologies were first introduced. It is not that new technologies are missing today, they are more of evolutions, not revolutions. The text below is not intended to cover every fine detail or instrument - I suggest referring to Wikipedia and other sites for this matter.
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Being a "home" musical player (you may say amateur...) I was always looked for new sounds. Keyboards, more then any other musical instrument can produce the sounds... you will see how.
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My first encounter with keyboards was with electric organs. In today's standards, they were primitive instruments: Based on analog oscillators, hard connected and produced sounds based on sinus oscillators. They sounded as variations of flutes, simply because flute is producing a sinus like waveform. Some classic names and sounds from this era are still with us - The Hammond organs and sounds as "Rock Organ" and "Jazz Organ".
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The first synthesizer, I was aware of, was Moog. It used the same concept of analog oscillators, but, control dials and switches, located on the front panel, tweaked sounds. This configuration enabled more synthetic sounds to be generated. It actually started a trend in the music production industry, where every arranger who wished to be considered modern, used those synthetic, unnatural sounds. New world of sounds for those days was possible. They had a limited character and mostly were non musical by today's standards.
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While Moog looked like a laboratory tool, there were others that started to look like today's musical keyboard: A portable keyboard with controls located nearby - Enabled real time, on performance sound changes (musician could be more expressive). Prophet and Roland's Jupiter-4 are the most significant and popular ones. They were polyphonic (Compared to Moog's usually monophonic sounds). Roland's tones, thick and with harmony generated by multi oscillators that performed together are still classic today. All was good, but they were all analog. Means, their generated tones were limited to the amount of hardware (Oscillators and filters) put inside.
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The Yamaha DX7 of the 80's started the revolution. It was a digital synthesizer, the first compact and affordable one. Able to produce sounds of various and completely different nature instruments. Some of the sounds acted much like the originals and new sounds, never heard before started to appear. The secret of this richness and completeness was the first utilization of DSP which backed by SW control. This was the first time that the HW was running user algorithms (or sound schemes). The HW was generic, so, it impose no limitation on the sound generation. The algorithms set the way the virtual oscillators were configured. The sound possiblities, this way, was a huge range. From simple organ like sounds (where the algorithm set the oscillators to work in parallel) to complex waveforms as piano and trumpet (where the algorithm set one oscillator modulating its successor). The method is known as FM synthesis. The DX7's picture is starting this section. One note - The FM synthesis was not simple to utilize for musician. They understood easily the analog synthesis, were the building blocks were simple. It was difficult and non intuitive to create new sound using FM synthesis. Luckily, Yamaha build into the DX7 a port that accepted memory modules with pre-configured sounds. It actually saved the DX7 from being a failure to become a great success. From now on, musical keyboard manufactures provided extensive sound presets along with fine detailed parameter controls.
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Other companies, as Roland and Korg had their own digital synthesis methods. They enable, As Yamaha's FM system, a large sounds set and continue the trend of SW controlled sound generation, running on generic DSP engines.
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The target of producing indistinguishable sounds compared with the real musical instruments had to continue. The best synthesizers were good, but, not up to the real world sounds. Memory modules became cheaper those days, which enabled musical keyboards with a huge amount of memory - The sample playback keyboards, or simply, samplers. They were loaded with real musical instruments waveforms, sampled at high resolution and further closed the gap between the real world sounds and the virtual ones. Large waveform libraries generated and create the option of playing anything that could be recorded. This was beyond imagination and musician started the ethnic trend (New Age music) that used tools that otherwise impossible to synthesis. Of course, using a digital sound generators enabled them to create complex arrangements which are more interesting then just a playback. It should be note that not everything was perfect. While synthesizers could act dynamically, changing the generated waveform on the fly, samplers were limited to what recorded. Tools as Piano which acts dynamically suffered mostly. Only later generations could handle this issue - See next paragraphs.
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The computing industry made a great progress since the DSP's used by the first digital synthesizers. They were much powerful and faster. They could be used to simulate things in real time - here comes the physical modeling. It should be remembered that we were still in the race of producing, synthetically, the true, real sounds. With physical modeling, every instrument was constructed of two sections: A resonator producing the sounds and a wave guide or a modulator which gave the sound its behaviour or character. For example, the hammer is the resonator of the piano while its wooden box producing the sounds, using the waves reflecting off the walls and interacting between themselves. The DSP's should be very fast to do everything in real time, as the player is hitting the Piano's keyboard. Any real musical instrument was accurately produced this way, while new combinations were possible. I was greatly disappointed to see that this concept was not become the synthesis method of choice - Maybe musicians wanted something simpler, intuitive with just sound presets to work with.
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So, where are we standing today. We are more mature. There are not any revolutions in the recent years, but evolutions. It may be said that modern synthesizers (Music production tool - see the Yamaha MOTIF below) have today something of everything. They are using digital synthesis - means you have virtual oscillators and filters. They are being fed with complex, memory resident, waveforms. So, we the best of two worlds - The complex waveforms of the samplers with the real time dynamics of the digital synthesizers. It can be a simple alternative to the more resource demanding physical modeling. It is worth mention that musical keyboards today have an integral effects DSP's which used to add depth and other powerful effects to the sounds. Some of the keyboards are even customize to produce classical vintage sounds. They are usually referred as Analog modeling and used to produce the early days analog synthesizer sounds.
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Along this story, I refer to keyboards, but, there is higher level of discussion. Every module I wrote about is available as a stand alone rack mounted box. It can be controlled by the MIDI interface. So, even guitar and wind instrument players can produce new sounds, not associated with their standard instruments... A different story.
