Synthesised Sound

• see also:
  • sound
  • waves
  • acoustics
  • music theory
  • recording technology
  • computers & sound

Analog synthesisers:

• brief history:
  • RCA synthesisers Mark I & II (1954) - monophonic
  • Moog synthesisers:
    • initially developed in 1965
    • became famous in 1967 when Carlos recorded "Switched on Bach"
    • 1st live synthesiser - the "Minimoog" was unveiled in 1971
  • early 1980's:
    • Roland Juno 106
    • Korg
    • Roland Planet & Jupiter modules
• 3 main elements:
  • voltage-controlled oscillator (VCO)
    • determines pitch of the sound - the greater the voltage, the higher the pitch
    • you can normally set the pitch range:
      • usually by selecting it in footages (eg. 8' which might be middleC, whereas 4' is an octave higher)
    • you can usually fine tune it so that it matches concert pitch or whatever pitch you require
      • this is also needed to maintain the tuning as these often became out of tune as they warmed up!
    • the pulse width can also be changed from a warm clarinet-like wave to a harsh nasal wave
    • you can usually choose a waveform eg. square, triangle (mellow sound) or sawtooth (reedy sound) wave
    • if a synthesiser has 2 VCO's you can have each set to a different pitch range & tuning & waveform & can choose to synchronise one VCO onto a harmonic of the other VCO
    • many used digitally controlled oscillators (DCOs) which are cheaper & stay in tune better than VCOs
  • voltage-controlled filter (VCF)
    • determines the timbre:
    • cutoff frequency - the greater the voltage, the higher the cut-off frequency & thus the more signal gets through
    • resonance
    • envelope
  • voltage-controlled amplifier (VCA)
    • determines the loudness
    • the greater the voltage, the higher the amplitude & thus loudness
    • amplitude vs time envelope controls the rate of rise and rate of decay of sound amplitude
      • attack
      • decay
      • sustain
      • release
• supplementary elements:
  • low frequency oscillator (LFO):
    • like the VCO but generates very slow frequencies which can be used to modulate that waves generated by either:
      • the VCO: if sine wave LFO then produces vibrato; if square wave LFO => trill;
      • the VCA: if sine wave LFO => tremolo; if square wave => echo-like effect;
  • high pass filter (HPF):
    • removes unwanted low frequencies 
  • noise generator:
    • adds unpitched sound to enable sounds like the wind or waves crashing on the shore.
  • chorus
• performance controls:
  • pitchbend: allows raising or lowering of the pitch whilst playing the notes
  • modulation: allows increasing intensity of the LFO modulation
  • portamento: creates a sliding effect between notes
  • glissando: plays all notes between two notes in semitone steps
• problems with analogs:
  • VCO's change tune with temperature
  • whilst able to give rich, warm sounds, had trouble reproducing bright, bell-like sounds

Digital synthesisers:

• FM synthesisers:
  • history:
    • in the mid-1980's Yamaha produced the DX-7 (with 6 operators) which changed the scene of synthesised sounds
    • the advent of midi commands & connections allowed universally compatible ability to control a number of synthesisers or sound modules from controllers such as piano-like keyboards or computers
    • by the late 1980's, FM synthesiser based sound cards were being added to computers to give them sound for the 1st time (apart from the beep noise) - see computers & sound
  • FM stands for frequency modulation:
    • a type of additive synthesis by taking a pure tone (a sine wave known as the carrier) & continually alter its tone with another sine wave (modulator) to produce a complex tone
    • initially the FM system was difficult to use, the programming of sounds was a hit & miss affair & thus only preset sounds were used (as they still are in FM synthesis computer sound cards)
    • a major breakthrough was the introduction of the concept of the operator which consists of the equivalent of a voltage-controlled sine wave generator and and envelope generator.
    • you can either use all the operators as carriers or use some as carriers & others as modulators to determine changes in the timbre produced by the carriers.
    • every voice has has a certain number of operators & the signal paths used are known as algorithms.
    • FM synthesis is not the easiest to understand or to program, but the results obtainable are a significant advantage, being much brighter than the subtractive synthesisers
• Digitally sampled sound:
  • this involves recording a real-life sound and converting it into a digital waveform which can then be replayed at different pitches
  • early versions had low sampling rates and only sampled sounds at a few pitches which made the sound deteriorate when played back at pitches distant from those sampled at.
  • with lowered cost of memory & faster computer chips, improved sampling rates were possible resulting in ever increasing fidelity.
  • the 1st commercial sampling modules were marketed in late 1980's and were expensive.
  • by the mid-1990's computer sound cards changed from FM synthesis to wave table lookup which meant that for each voice, the wave form for it was looked up in a memory bank & meant more realistic reproduction of real instruments. see computers & sound
  •