What Makes Analog so Phat?

Vintage Analogue Analog Synth Warm Phatt Fat Punchy WaveformThe basis of all synthesizers is the sound source, and in the case of analogue systems, this is either an oscillator or a noise generator. While all synthesizers have at least one sound source, many have two or more and in the case of the big modular synthesizers that dominated albums like Switched on Bach by Walter Carlos (now Wendy Carlos), the number of sound sources was only limited by your budget, available space in your cabinet(s) and the number of patch cables you had.

Modular synthesizers are just that, synthesizers made up of different modules, and each module is a synthesizer component such as an oscillator, amplifier, envelope generator, filter or mixer, or a combination of different components. The modules are typically slotted into a frame to provide power and keyboard control, and the modules are =connected to each other with patch cables.  If you wanted to add another sound source, you simply pick a new module, slot it in the rack and connect the patch cables into the rest of the synthesizer.

Despiite manufacturing tolerances, every analogue oscillator is effectively unique as it is built up from components such as resistors, capacitors and valves (or transistors in more modern designs) which make them slightly more or less than the values shown on the device itself. As a result, this can add distortion to the tonal characteristics of the oscillator's sound. Add to this, the fact that the oscillators tuning can drift over time, or because of heat, you can suddenly have a system that at best adds additional tone to the sound, or at worst is totally unreliable!. It is a known fact that some of today's most revered analogue synthesizers can be temperamental when used live on stage, which makes some wonder what the appeal of these systems really is. However, these systems can create sounds that are still unachievable on some of today's best digital systems.

The inherent instability of oscillators makes analogue synthesizers with two or more of them have a unqiue character, as the actual tuning is never quite same between them.  This introduces 'beating' and ‘phasing’ into the sound, as the peaks and troughs of the waveforms being generated accentuate and partially cancel out and accentuate each other over time. Also, the slight detuning between oscillators gives additional depth to the overall sound, almost in the same way as a choir all singing the same note sounds fuller and more broad than a single singer singing the same note. To explain, besides the additional volume of the others in the choir, everyone is in reality singing a unique note as they are all ever so slightly out of tune with each other, and all have different voices, as every voice box is unique. The fact that we can't perceive this (unless a singer is particularly bad) does not mean that it is not happening. If they were all singing exactly the same, the only difference between the solo singer and the choir would be volume, and no additional depth of sound.

Pure Square Waveform vs. Analogue Square WaveformAnother benefit of the analogue oscillator's imperfections is that it is not very good at making the sound waves it's supposed to, which in turn, adds additional harmonics to the sound. For example, the picture to the left shows the difference between a perfect square waveform (top) and that of a typcial analogue oscillator (bottom).  Where the analogue sqaure waveform should have sides that go straight up and down, but the best an analogue circuitcan produce is a steep slope either side of the pulse, and while the top and bottom are supposed to be flat, there is a small peak at the top and a small trough at the bottom, with the flat bit being not quite flat. While this may sound undesirable, these imperfections actaully add that alluring character to the overall sound, which makes true, vintage analogue synthesizers so sought after today. It's interesting to note that for many years, musicians used these systems blissfully unaware that they were not getting the exact waveform they were selecting, so the situation was never as bad as it may seem when described.

Now, it would be very boring if every synth sound played straight on and off when a key is pressed, so a system known as an envelope generator is used to control how the sound is controlled over time including it's begiining, duration, and ending.  This is known as the ADSR envelope whic stands for Attack, Decay, Sustain, and Release.

The attack controls how the sound starts when the key is pressed. If the attack is set to fast, it reaches it's maximum volume quickly and is ideal for percussive and piano type sounds, while a slow attack builds the sound up slowly and is good for atmospheric or background sounds, such as a string or ambient pad sound. The decay controls how quickly the sound reaches the volume for sustain, while sustain itself sets how the sound will behave while the key is held down, and depending on your synth, can either control how quickly the volume goes down over time, or at what volume the sound will be held at while the key is held. Release controls how the sound behaves once the key is released; a quick release forces the sound to stop quickly while a slow release allows the sound to linger and fade over time. Some synths will provide additional functions and parameters for each of these envelopes.  As mentioned with the oscillators, these envelopes are made of similar components making them susceptible to heat and component fluctuations, so the envelope generator may generate curved slopes when the diagrams in all synthesizer manuals show straight lines. More individual character anyone?

Most of the time, there will only be two envelope generators - one on the filter, the other on the amplifier section, neither of which we have covered yet.  On some systems you can find an envelope generator on each oscillator, allowing you to have more control over how each sound source affects the overall tonal quality over time. But before we move on to the next bit of a general synthesizers design, we have to mix all the sound sources together into one audio signal, and this is done in the imaginatively named mixer section. Unlike a large hardware mixer found in music studios, all you can generally do here is adjust the level of each sound source.

Perched in-between the envelopes and the rest of the synthesizer is the Low Frequency Oscillator (LFO), which can be used to add fluctuations (i.e. character) to the sound.  Depending on the design, this may have a selection of waveforms to modulate the sound, also it may have a selection of destinations for the LFO to modulate, such as filter frequency, filter Q settings (Described next), one or more of the oscillators, or even a number of possible destinations.  On occasion, there may even be more than one LFO, each with different settings.

Analog Synth Sound Schematic Diagram VCO VCF VCA LFO Delay Attack Sustain ReleaseNow on to the most powerful section of most analogue synthesizers, the filter section. A simple frequency filter and Q control can be found on many filter sections.  The frequency filter selects the frequency range to be affected, while the Q function either narrows down or widens the range of frequencies to be affected. With the Q filter set quite high, the filter can go into self-oscillation, generating frequencies of it's own. More complex filters have different modes of operation, most simple filters are low pass filters, which allow frequencies below the frequency setting to pass through, while frequencies higher than this are filtered out. Other modes include: high pass, where frequencies below the frequency setting are filtered out; notch filter, where only a specific frequency is let through and all others filtered out; band filter, where a band of frequencies are let through; and comb filter, which lets groups of frequencies through while filtering out frequencies in-between the different groups.

Since the output of the oscillator(s) is fairly rich and fat with different frequencies, various different filter modes are needed affect to reduce and/or focus these frequenciing to produce the desired sound. To add some character to sounds, many of the bigger and more powerful synthesizers had envelopes to control how frequencies were filtered over time, which created a sound that evolved over time.

If you have a stereo system with a graphic equaliser, this is in effect a basic filter, though one more generalised and not as specific or as dedicated as a synthesizers filter.  Each control affects a certain band of frequencies, which you can adjust to taste.  But unlike a filter described above, you can’t cut frequencies out altogether.

Now once again, the nature of analogue components comes into play, and the whole nature of the filter is affected. The most widely recognised of these is the filter on the Moog Minimoog synthesizer, produced by Bob Moog from the late 60's until the mid 70's,and later resurrected in the Moog Voyager in 2003. This filter is based around what is called a ladder design, which is patented by Moog Music and one of the most imitated filter designs in synthesizer history.

The final part of a typical analogue synthesizer, is the amplifier. Generally this just has envelope generator controls to shape the overall output of the sound, followed by a final output level. Not much to add really, as all the tonal quality of the sound is done in the earlier stages.

These different sections are often known as VCO's (Voltage Controlled Oscillators), VCF (Voltage Controlled Filter) and VCA (Voltage Controlled Amplifier) sections and are common to all true analogue synthesizers, I say true analogue, as towards the mid 80's, after the birth of the MIDI protocol, a new breed of synthesizer had a fleeting moment in the development of the synthesizer, the hybrid synthesizer.

Hybrids were mainly analogue, but used Digitally Controlled Oscillators (DCO's) as the sound source. The Korg DW-6000 and 8000 are good examples of hybrid synthesizers, as is the poly-600, though they do lack some of the character of a true analogue system. Korg also made the DS-1 sampler, which replaced the DCO's of the DW-8000 with sounds sampled by the user and was capable of some unique sounds, even though the sampling was quite limited.

While the age of the analogue synthesizer was over by the mid to late 80’s, a number of MIDI controlled analogue systems were made and marketed, including the Matrix 1000 from synthesizer legend Oberheim, and the MS6 from the plucky U.K. company Cheetah.  While these are analogue synthesizers at heart, all the sections are digitally controlled and have more precision tuning compared to their earlier contemporaries.  However, if you want an analogue system in your MIDI rack without the headaches of adding MIDI interfaces to classic equipment, or remembering where each knob, slider and switch was for that killer lead sound you created last night, these devices could well be what you are looking for.